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🔬 COMPLETE LECTURE: Musculoskeletal, Skin & Connective Tissue Pathology

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PAGE 1 - GOUT & CALCIUM PYROPHOSPHATE DEPOSITION (CPPD) DISEASE

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🟣 GOUT

"Acute inflammatory monoarthritis caused by precipitation of monosodium urate crystals in joints."

• Monoarthritis = inflammation of ONE joint at a time. "Mono" = one. So unlike rheumatoid arthritis where many joints swell together, in gout, usually just ONE joint becomes red, hot, and extremely painful.
• Precipitation = like salt crystallizing out of oversaturated water. When there's too much uric acid in the blood, it crystallizes out and deposits in joints.
• Monosodium urate crystals = the specific type of crystal formed from uric acid (a waste product from breakdown of purines - the building blocks of DNA). Think of them like tiny needles made of salt depositing inside a joint.

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"Risk factors: male sex, hypertension, obesity, diabetes, dyslipidemia, alcohol use, thiazide diuretics"

• Male sex: Males naturally produce more uric acid. Also, estrogen in females actually helps kidneys excrete uric acid - so women are relatively protected until after menopause.
• Hypertension, obesity, diabetes: All these conditions reduce how efficiently your kidneys excrete uric acid.
• Dyslipidemia (abnormal blood fat levels): Associated with metabolic syndrome which impairs uric acid excretion.
• Alcohol use: Alcohol increases uric acid production AND decreases its excretion from the kidneys. Beer is especially bad because it also contains purines.
• Thiazide diuretics (water pills like hydrochlorothiazide): These are blood pressure drugs. They reduce kidney excretion of uric acid as a side effect, raising blood uric acid levels.

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"The primary risk factor is hyperuricemia"

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"Underexcretion of uric acid (90% of patients) - largely idiopathic, potentiated by renal failure"

• Underexcretion = the kidneys are not removing enough uric acid from the blood into the urine.
• 90% of patients = this is the most common cause - the body makes a normal amount of uric acid, but the kidneys just don't flush it out efficiently enough.
• Idiopathic = medical word meaning "we don't know why" - it just happens in some people genetically.
• Renal failure = kidney failure makes this worse because damaged kidneys excrete even less uric acid.

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"Can be exacerbated by certain medications (eg, thiazide diuretics)"

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"Overproduction of uric acid (10% of patients) - Lesch-Nyhan syndrome, PRPP excess, T cell turnover"

• Overproduction = the body is making too much uric acid in the first place.
• Lesch-Nyhan syndrome = a rare genetic disease where an enzyme called HGPRT is absent. This enzyme normally recycles purines; without it, purines are broken down into uric acid excessively. Patients get gout, intellectual disability, and self-mutilating behavior.
• PRPP excess = PRPP (phosphoribosyl pyrophosphate) is a molecule that drives purine synthesis. Too much PRPP = too many purines made = too much uric acid produced.
• T cell turnover = T cells are white blood cells. In cancer treatments (chemotherapy) or conditions with rapid cell death, DNA from dying cells is broken down into purines, then into uric acid. This is why cancer patients on chemo can get gout.

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"Combined mechanism - alcohol use and von Gierke disease"

• Von Gierke disease = a rare metabolic disease (type 1 glycogen storage disease) where the body can't properly process glycogen (stored sugar). This leads to lactic acidosis AND overproduction of uric acid. Lactic acid competes with uric acid for kidney excretion.
• Alcohol = both increases production AND decreases excretion - the double hit.

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"Crystals are needle shaped and birefringent under polarized light (yellow under parallel light, blue under perpendicular light)"

• Needle-shaped = the uric acid crystals look like tiny needles, which explains why the joint is so painful - imagine microscopic needles stabbing your joint lining.
• Birefringent = when light shines through these crystals, they bend the light in two directions. This creates color effects.
• Yellow under parallel light, blue under perpendicular light = This is the classic exam answer. The color changes based on the angle of the polarizer. The memory trick: "yell-OW, gout go" (Yellow = parallel polarized light = gout/urate crystals). Also called negatively birefringent.

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"Serum uric acid levels may be normal during an acute attack"

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"Asymmetric joint distribution. Joint is swollen, red, and painful. Classic manifestation is painful MTP joint of big toe (podagra)."

• Asymmetric = affects one side or random joints, not symmetric like rheumatoid arthritis.
• MTP joint = metatarsophalangeal joint = the joint where your big toe meets your foot.
• Podagra = gout specifically in the big toe. The classic image: a man wakes up at 3 AM screaming because even a bedsheet touching his big toe is unbearable.

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"Tophus formation (often on external ear, olecranon bursa, or Achilles tendon)"

• Tophus (plural: tophi) = chalky white deposits of monosodium urate crystals that build up under the skin over years of chronic gout. Think of them as "gout lumps."
• External ear = you can sometimes see white chalky bumps on the ear cartilage.
• Olecranon bursa = the fluid sac at the tip of the elbow.
• Achilles tendon = the tendon at the back of your heel. These appear in CHRONIC gout (repeated attacks over years).

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"Acute attack tends to occur after a large meal with foods rich in purines (eg, meat, seafood), trauma, surgery, dehydration, diuresis, or alcohol consumption (↑ blood lactate from metabolism → ↑ resorption of uric acid → hyperuricemia)"

• Purines = found abundantly in red meat, organ meats (liver, kidney), shellfish, beer. When digested, these become uric acid.
• Trauma/Surgery = causes rapid cell breakdown, releasing DNA purines.
• Dehydration/Diuresis = less fluid means uric acid becomes more concentrated in blood.
• Alcohol → ↑ blood lactate = Alcohol is metabolized to lactic acid. Lactic acid competes with uric acid for the same kidney transporter. When lactic acid wins, uric acid stays in the blood (resorbed back rather than excreted), raising blood uric acid levels → crystal formation → gout attack.

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TREATMENT:

• NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) like ibuprofen, indomethacin = reduce inflammation and pain quickly.
• Glucocorticoids = steroids like prednisone = powerful anti-inflammatories, used if NSAIDs are contraindicated (e.g., kidney disease).
• Colchicine = a drug from the crocus plant that prevents white blood cells from migrating into the joint (reduces inflammation). Works by disrupting microtubules - the "skeleton" that white cells use to move.

• Allopurinol = inhibits xanthine oxidase, the enzyme that makes uric acid. Less enzyme activity = less uric acid produced. NEVER start during an acute attack (can prolong it).
• Probenecid = makes kidneys excrete MORE uric acid. Works on kidney tubule transporters.

• Xanthine oxidase = the enzyme in the last step of uric acid production. Block it = block uric acid production. Febuxostat is a newer, more potent xanthine oxidase inhibitor than allopurinol.

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🟢 CALCIUM PYROPHOSPHATE DEPOSITION DISEASE (CPPD) / PSEUDOGOUT

"Formerly called pseudogout"

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"Deposition of calcium pyrophosphate crystals within the joint space"

• Calcium pyrophosphate = a different chemical (calcium + pyrophosphate, a phosphate compound) that crystallizes in joints.
• These crystals are NOT needle-shaped like gout crystals. They're rhomboid (diamond-shaped).

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"Occurs in patients > 50 years old; both sexes affected equally"

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"Usually idiopathic, sometimes associated with hemochromatosis, hyperparathyroidism, joint trauma"

• Hemochromatosis = iron overload disease. Excess iron deposits in joints, disrupts cartilage metabolism, promotes calcium pyrophosphate deposition.
• Hyperparathyroidism = overactive parathyroid gland = too much PTH hormone = elevated calcium in blood = more calcium available to deposit in joints.
• Joint trauma = direct injury to cartilage can trigger crystal deposition.

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"Pain and swelling with acute inflammation (pseudogout) and/or chronic degeneration (pseudo-osteoarthritis). Most commonly affected joint is the knee."

• The knee is the #1 joint affected in CPPD (contrast with gout where it's the big toe).
• Pseudo-osteoarthritis = looks like regular wear-and-tear arthritis but is actually from crystal damage.

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"Chondrocalcinosis (cartilage calcification) on x-ray"

• Chondro = cartilage, calcinosis = calcium deposits.
• On X-ray, you can see white calcification within the cartilage of the knee. This is a key diagnostic finding - you see the calcium deposits lighting up on the X-ray.

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"Crystals are rhomboid and weakly positively birefringent under polarized light (blue when parallel to light)"

• Rhomboid = diamond/parallelogram shape (different from gout's needle shape).
• Weakly positively birefringent = when you shine polarized light, the crystals appear BLUE when parallel to the polarizer.
• Memory trick: "Blue when parallel = CPPD/Calcium" → The BLUE Ps of CPPD.

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"The blue P's of CPPD - blue (when parallel); positive birefringence, calcium Pyrophosphate, Pseudogout"

• Blue when Parallel = Positive birefringence = calcium Pyrophosphate = Pseudogout Everything starts with P (or relates to blue)!

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"Acute treatment: NSAIDs, colchicine, glucocorticoids. Prophylaxis: colchicine."

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PAGE 2 - SERONEGATIVE ARTHROPATHIES: Psoriatic Arthritis, Ankylosing Spondylitis, Inflammatory Bowel Disease Arthritis, Reactive Arthritis

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SERONEGATIVE ARTHROPATHIES - What does "seronegative" mean?

• HLA-B27 genetic association
• Sacroiliac joint involvement (the joint between the spine and pelvis)
• Enthesitis (inflammation at points where tendons/ligaments attach to bone)

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PSORIATIC ARTHRITIS

"Arthritis without rheumatoid factor (no anti-IgG antibody). Strong association with HLA-B27 (MHC class I seronegative PA type). Subtypes..."

• No anti-IgG = "seronegative" - the blood test for RA is negative.
• HLA-B27 = a gene variant (Human Leukocyte Antigen type B27). Think of HLA genes as your immune system's ID badge. HLA-B27 is the badge that all seronegative spondyloarthropathies share. If you carry this gene, you're more susceptible to these conditions.
• MHC class I = Major Histocompatibility Complex class 1. This is the protein complex on cell surfaces that displays bits of protein to the immune system. HLA-B27 is part of this complex.

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"Pain associated with morning stiffness (eg, Achilles, dactylitis, enthesitis, 'sausage fingers')"

• Morning stiffness = all inflammatory arthropathies cause stiffness worse in the morning (because inflammation sets overnight when you're not moving). Unlike osteoarthritis where stiffness improves with rest.
• Dactylitis = inflammation of an entire finger or toe, making it look like a "sausage." The ENTIRE digit swells, not just one joint. This is very characteristic of psoriatic arthritis.
• Enthesitis = inflammation at the entheses = the points where tendons and ligaments attach to bone. Achilles tendon insertion, plantar fascia, etc.

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"Asymmetric and patchy involves nail lesions. DIP on X-ray and 'pencil-in-cup' deformity"

• Asymmetric = affects random joints on either side, not the same joints on both sides simultaneously.
• Nail lesions = pitting (tiny dents in the nail), onycholysis (nail lifting off the nail bed). Psoriasis affects both skin and nails.
• DIP = Distal Interphalangeal joint = the joints closest to the fingertips. Psoriatic arthritis characteristically affects DIP joints (contrast: rheumatoid arthritis spares DIP, involves MCP and PIP).
• Pencil-in-cup deformity = on X-ray, one bone end erodes and widens while the other sharpens, creating an appearance like a pencil sitting in a cup. This is the hallmark X-ray finding of severe psoriatic arthritis.

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"Symmetric involvement of spine and sacroiliac joints → ankylosis (joint fusion), iritis, aortic regurgitation"

• Sacroiliac joints = SI joints = where the spine (sacrum) meets the pelvis (ilium). Inflammation here causes low back pain.
• Ankylosis = fusion of joints. The inflamed joint eventually scars over and the bones fuse together, causing permanent stiffness.
• Iritis/Uveitis = inflammation of the iris (colored part of eye) or uvea (middle layer of eye). A classic extra-articular (outside the joint) feature of seronegative spondyloarthropathies.
• Aortic regurgitation = the aortic heart valve leaks backward. The chronic inflammation can damage the aortic root, causing the valve leaflets to not close properly.

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ANKYLOSING SPONDYLITIS

"Bamboo spine (vertebral fusion) on X-ray"

• Ankylosis = fusion, Spondylitis = spinal inflammation. The entire spine becomes inflamed and eventually fuses together.
• Bamboo spine = the X-ray appearance where the fused vertebrae look like a bamboo stalk - smooth, continuous bone bridging from one vertebra to the next (called syndesmophytes = bony bridges).
• The patient loses ALL spinal flexibility. Can't bend forward or backward.

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"Costovertebral and costosternal ankylosis may cause restrictive lung disease"

• Costovertebral = where ribs meet the spine.
• Costosternal = where ribs meet the sternum (breastbone).
• When these joints fuse, the chest wall can't expand properly → restrictive lung disease = the lungs can't fill completely because the chest is literally rigid.

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"More common in males, with age of onset usually 20-40 years"

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INFLAMMATORY BOWEL DISEASE (IBD) ARTHRITIS

"Crohn disease and ulcerative colitis are often associated with spondyloarthritis"

• The gut and the joints share immune pathways. The chronic gut inflammation "spills over" to joints.
• Can affect peripheral joints (arms, legs) or the spine/sacroiliac joints.

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REACTIVE ARTHRITIS

"'Can't see, can't pee, can't bend my knee.' Associated with infections by Shigella, Campylobacter, Salmonella, Chlamydia, Yersinia"

1. Conjunctivitis = "Can't see" = eye inflammation (red eyes)
2. Urethritis = "Can't pee" = inflammation of the urethra (causes painful, burning urination)
3. Arthritis = "Can't bend my knee" = joint inflammation

• Shigella (dysentery bacterium)
• Campylobacter (food poisoning)
• Salmonella (food poisoning)
• Chlamydia (sexually transmitted)
• Yersinia (food/water-borne)

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"Commonly associated with hyperkeratotic skin lesions in the palms and soles (keratoderma blenorrhagica)"

• Keratoderma blenorrhagica = a fancy term for thick, warty, scaly skin on palms and soles. It's almost indistinguishable from psoriasis.
• Also get circinate balanitis = a painless sore on the head of the penis.

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PAGE 2 (continued) - Systemic Juvenile Idiopathic Arthritis, Sjögren Syndrome, Septic Arthritis, Osteomyelitis

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SYSTEMIC JUVENILE IDIOPATHIC ARTHRITIS (Systemic JIA)

"Systemic arthritis seen in ~ 16 years of age. Usually presents with daily spiking fevers, macular rash, arthritis (commonly 2+ joints). Associated with leukocytosis, thrombocytosis, anemia. ↑ ESR, ↑ CRP"

• Juvenile = occurs in children (by definition < 16-18 years old).
• Idiopathic = cause unknown.
• Daily spiking fevers = one of the most characteristic features. The fever goes up to 39-40°C once or twice daily then comes back down. This "quotidian" (daily) fever pattern is a hallmark.
• Macular rash = flat, salmon-pink, evanescent (comes and goes) rash, usually appearing with the fever spikes. When fever is up, rash appears; when fever breaks, rash fades.
• Leukocytosis = elevated white blood cells (fighting inflammation).
• Thrombocytosis = elevated platelets (reactive to inflammation).
• Anemia = low red blood cells (chronic inflammation suppresses red cell production).
• ↑ ESR = Erythrocyte Sedimentation Rate. Red blood cells clump more when there's inflammation protein (fibrinogen) in blood, so they fall faster in a tube. Elevated = inflammation marker.
• ↑ CRP = C-Reactive Protein. Liver produces this acutely when there is inflammation. A sensitive marker of active inflammation.

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SJÖGREN SYNDROME

"Autoimmune disorder characterized by lymphocytic destruction of exocrine glands (especially lacrimal and salivary)"

• Autoimmune = the immune system attacks the body's own tissues.
• Exocrine glands = glands that secrete through ducts (as opposed to endocrine glands that secrete hormones into blood). Examples: salivary glands, lacrimal (tear) glands, sweat glands.
• Lacrimal glands = tear-producing glands. Destroy these = no tears = dry eyes.
• Salivary glands = saliva-producing glands. Destroy these = no saliva = dry mouth.
• Lymphocytic = the type of white blood cell (lymphocytes) doing the attacking.

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"Predominantly affects females 40-60 years old"

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Findings:

• Keratoconjunctivitis = inflammation of the cornea (kerato) and conjunctiva (the white of the eye).
• Sicca = dry (Latin). So this literally means "dry eye inflammation."
• Without tears, the cornea dries out and gets damaged.

• Xerostomia = dry mouth (xero = dry, stomia = mouth).
• Without saliva, the tongue cracks and fissures develop.
• Patients can't swallow dry food without water.
• ↑ dental caries (cavities) because saliva normally protects teeth.

• The dry eye feels like sand in the eyes - a common complaint patients use.

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"Presence of antinuclear antibodies; rheumatoid factor (can be positive in the absence of rheumatoid arthritis)"

• Antinuclear antibodies (ANA) = antibodies against the nucleus of cells. Positive in many autoimmune diseases.
• Anti-SSA (Ro) and Anti-SSB (La) = the SPECIFIC antibodies for Sjögren syndrome. "SS" in the name stands for Sjögren syndrome!
• These are the antibodies that matter on the USMLE.

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"Focal lymphocytic enlargement; present as parotid enlargement (MALT lymphoma may develop)"

• Parotid gland = the largest salivary gland, located in the cheek area.
• Chronic lymphocyte infiltration of the salivary glands can cause visible swelling of the parotid glands (the cheeks look puffy).
• MALT lymphoma = Mucosa-Associated Lymphoid Tissue lymphoma. This is a low-grade cancer of B-lymphocytes that can develop in the chronically inflamed glands of Sjögren patients. Risk is 40x higher than the general population.

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"Anti-SSA and anti-SSB may also be seen in SLE"

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Complications: dental caries, mucosa-mucosa issues, dyspareunia

• Dyspareunia = painful sexual intercourse (because vaginal dryness also occurs from dry gland involvement elsewhere).

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"Bilateral parotid enlargement"

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SEPTIC ARTHRITIS

"S. aureus, Streptococcus, and Neisseria gonorrhoeae are common causes. Usually monoarticular."

• Septic arthritis = INFECTED joint. Bacteria get into the joint space (through the blood, direct injury, or spreading from nearby bone infection).
• Monoarticular = one joint affected.
• S. aureus (Staphylococcus aureus) = the #1 cause of septic arthritis overall (including in children and adults).
• Streptococcus = strep bacteria.
• Neisseria gonorrhoeae = the bacterium causing gonorrhea (sexually transmitted infection). This is the MOST COMMON cause of septic arthritis in sexually active young adults.

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"Affected joint is often swollen, red, and painful. Synovial fluid purulent (WBC > 50,000/mm3)"

• Synovial fluid = the lubricating fluid inside joints.
• Purulent = filled with pus (white blood cells flooding in to fight the infection).
• WBC > 50,000 = hugely elevated white cells = infection (compare: non-inflammatory fluid has < 200 WBC; inflammatory like gout has 2,000-50,000).

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"Complications: osteomyelitis, chronic pain, irreversible joint damage; sepsis. Treatment: aspiration and drainage (±debridement) to prevent irreversible joint damage, septicemia, antibiotics."

• Debridement = surgical cleaning out of infected/dead tissue.
• If untreated, bacteria eat away at the cartilage and bone → permanent joint destruction.

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"Disseminated gonococcal infection - STI that presents as either purulent arthritis (eg, knee) or triad of polyarthralgia, tenosynovitis (eg, hand), dermatitis (eg, pustules)"

• Disseminated = spread through the blood from the original infection site to other organs.
• Polyarthralgia = pain in multiple joints.
• Tenosynovitis = inflammation of the tendon AND its sheath (the tunnel the tendon slides through). Extremely painful.
• Pustules = small pus-filled skin lesions - appear on the skin in disseminated gonococcal infection.

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OSTEOMYELITIS

"Chronic or acute infection of the bone"

• Osteo = bone, myel = marrow, itis = inflammation/infection.
• Bacteria infect the bone itself, eating into the bone marrow.

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"S aureus most common (overall). S epidermidis (prosthetics). P aeruginosa (plantar puncture wounds). Salmonella (sickle cell anemia)."

• S. aureus = #1 overall cause of bone infection.
• S. epidermidis = a skin bacterium that contaminates prosthetic implants (artificial hip/knee joints) because it forms biofilms (protective slime coatings).
• P. aeruginosa (Pseudomonas aeruginosa) = associated with puncture wounds through the sole of a shoe (like stepping on a nail). The rubber of shoe soles harbors Pseudomonas.
• Salmonella = specifically in sickle cell disease patients. In sickle cell, the spleen (which normally fights encapsulated bacteria) is damaged → bacteria like Salmonella can get into the bloodstream and seed the bone.

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"Spread is hematogenous (usually in children, affecting the metaphysis of the long bones)"

• Hematogenous = spread through the blood (hema = blood, genous = origin).
• Metaphysis = the growth plate area of long bones (like the femur/tibia). In children, this area has a rich blood supply with sluggish flow → bacteria can lodge there easily.
• In adults, infection is more common post-traumatic or post-surgery.

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"Diagnosis: x-ray (bone destruction and periosteal elevation if chronic), MRI, bone biopsy with cultures and blood cultures. Treatment: antibiotics (+/- surgery)"

• Periosteal elevation = on X-ray, the outer covering of bone (periosteum) lifts up as pus accumulates underneath. This takes 7-10 days to appear on plain X-ray.
• MRI = the best early imaging tool because it shows bone marrow edema (swelling inside the bone) before bone destruction is visible on X-ray.
• Bone biopsy = taking a sample of bone to culture (grow bacteria) and identify the exact organism.

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PAGE 4 - SYSTEMIC LUPUS ERYTHEMATOSUS (SLE)

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🔴 SLE

"Systemic, remitting, and relapsing autoimmune disease. Organ damage primarily due to a type III hypersensitivity reaction and, to a lesser degree, a type II hypersensitivity reaction."

• Systemic = affects the WHOLE body - kidneys, skin, joints, brain, heart, blood, lungs. Not just one organ.
• Remitting and relapsing = it has "flares" (when symptoms worsen) and "remissions" (when symptoms quiet down). It goes back and forth.
• Type III hypersensitivity = immune complex-mediated. Here's the explanation:
  • In SLE, the body makes antibodies against its OWN DNA (anti-dsDNA antibodies) and other nuclear components.
  • These antibodies bind to their targets → form immune complexes (antibody + antigen bundles).
  • These immune complexes float through the blood and deposit in blood vessel walls, kidneys, skin, joints.
  • Once deposited, they activate the complement system → inflammation and tissue damage.
  • Think of it like debris clogging a pipe.
• Type II hypersensitivity = antibody directly attacking a cell surface (e.g., antibodies against red blood cells causing hemolytic anemia, or against platelets causing thrombocytopenia).

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"Associated with deficiency of early complement proteins (eg, C1q, C4, C2) → ↓ clearance of immune complexes"

• Complement system = a cascade of blood proteins that help destroy pathogens AND clear up immune complexes (debris).
• C1q = the first protein in the classical complement pathway. C1q normally binds to immune complexes and helps clear them.
• When C1q/C4/C2 are deficient, immune complexes PILE UP instead of being cleared → they deposit in tissues → inflammation → SLE-like disease.
• This is why people with inherited complement deficiencies are highly prone to SLE.

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"Classic presentation: facial rash (spares nasolabial folds), joint pain, and fever in a female of reproductive age"

• Facial rash = the butterfly/malar rash. A red rash across the cheeks and bridge of the nose, shaped like a butterfly.
• Spares nasolabial folds = critically, the rash does NOT go into the creases beside the nose/mouth (the laugh lines). This helps distinguish it from other rashes.
• Female of reproductive age = SLE has a 9:1 female:male ratio. Estrogen seems to promote autoimmunity. Peak age 20-40 years.

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"↑ prevalence in Black, Caribbean, Asian, and Hispanic populations in the US"

• SLE is much more common and more severe in these populations. Black women have 3x the incidence of white women and worse outcomes.

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"Libman-Sacks Endocarditis (LSE in SLE)"

• Endocarditis = inflammation/infection of the heart valve lining.
• Libman-Sacks = a specific type of non-infectious endocarditis in SLE.
• Small, warty, sterile (no bacteria) vegetations form on BOTH sides of the mitral valve (and other valves).
• Normal infective endocarditis puts vegetation only on one side. Libman-Sacks = BOTH sides.
• The mnemonic: LSE in SLE = Libman-Sacks Endocarditis in Systemic Lupus Erythematosus.

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"Lupus nephritis (glomerular deposition of DNA-anti-DNA immune complexes) can be nephritic or nephrotic (causing hematuria or proteinuria). Most common and severe type is diffuse proliferative."

• Glomerular = in the tiny filtering units of the kidney (glomeruli). The kidney has millions of these microscopic filters.
• DNA-anti-DNA immune complexes = bundles of DNA + antibodies-against-DNA lodge in the kidney filter walls.
• Nephritic = blood in urine (hematuria), hypertension, reduced kidney function. Caused by inflammation breaking kidney filter walls.
• Nephrotic = massive protein in urine (proteinuria), swelling, low blood albumin. Caused by damage to the filtration barrier.
• Diffuse proliferative = the most severe pattern - involves almost all glomeruli (diffuse) with proliferating cells. Aggressive immunosuppression needed.

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"Common causes of death in SLE: renal disease, infections, cardiovascular disease (accelerated CAD). Lupus patients die with redness in their cheeks."

• Accelerated CAD = Coronary Artery Disease (heart artery blockages) develops faster in SLE patients due to:
  1. Chronic inflammation damaging blood vessels.
  2. Antiphospholipid antibodies promoting clotting.
  3. Steroid treatment causing weight gain, diabetes, high cholesterol.
• "Die with redness in their cheeks" = they have the malar (butterfly) rash on their cheeks until the end. A poignant way to remember the cause of death!

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"In an anti-SSA positive pregnant patient, ↑ risk of newborn developing neonatal lupus → congenital heart block, periorbital/diffuse rash, transaminitis, and cytopenias at birth"

• Anti-SSA antibodies from the mother cross the placenta (the barrier between mother and baby during pregnancy).
• These maternal antibodies attack the baby's tissues.
• Congenital heart block = the antibodies attack the electrical conduction tissue of the baby's heart, causing slow heart rate (bradycardia). This can be permanent.
• Transaminitis = elevated liver enzymes (anti-SSA attacking the liver).
• Cytopenias = low blood cell counts (anemia, low platelets, low white cells).

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RASH OR PAIN mnemonic for SLE criteria (the list in red):

• Rash (malar/discoid)
• Arthritis (non-erosive - doesn't destroy bone, unlike RA)
• Serositis (inflammation of body linings - pleuritis = lungs, pericarditis = heart)
• Hematologic disorders (cytopenias - low blood cells)
• Oral/nasopharyngeal ulcers (painful mouth sores, usually painless)
• Renal disease (lupus nephritis)
• Photosensitivity (skin rashes worsen with sun exposure)
• Antinuclear antibodies (ANA - the screening test)
• Immunologic disorder (anti-dsDNA, anti-Sm, antiphospholipid antibodies)
• Neurologic disorders (seizures, psychosis)

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MIXED CONNECTIVE TISSUE DISEASE (MCTD)

"Features of SLE, systemic sclerosis, and/or polymyositis. Associated with anti-U1 RNP antibodies (speckled ANA)."

• An overlap syndrome - patients have features of multiple diseases simultaneously.
• Anti-U1 RNP = the specific antibody. RNP = ribonucleoprotein (a cellular protein complex).
• Speckled ANA = the ANA immunofluorescence pattern looks like a speckled/spotted pattern (vs. homogeneous in SLE, peripheral/rim in anti-dsDNA positive SLE).

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ANTIPHOSPHOLIPID SYNDROME (APS)

"1° or 2° autoimmune disorder (most commonly in SLE)"

• Primary (1°) = occurs on its own.
• Secondary (2°) = occurs as part of another disease, most commonly SLE.

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"Diagnosed based on clinical criteria including history of thrombosis (arterial or venous) or recurrent abortion along with laboratory findings of lupus anticoagulant, anticardiolipin, anti-β₂ glycoprotein I antibodies."

• Antiphospholipid antibodies = antibodies against phospholipid-protein complexes in blood vessel walls and on platelets.
• These antibodies paradoxically PROMOTE clotting (thrombosis).
• Thrombosis = blood clot formation inside blood vessels.
• Recurrent abortion = these antibodies cause clotting in the placental blood vessels → placenta loses blood supply → repeated miscarriages.
• Lupus anticoagulant = despite its name, it actually CAUSES clotting (not anticoagulation). The name is confusing because it was first found in lupus patients and it prolongs clotting tests in the lab.

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"Anticardiolipin antibodies can cause false-positive VDRL/RPR"

• VDRL/RPR = blood tests for syphilis. These tests detect antibodies against cardiolipin (a phospholipid).
• Since antiphospholipid syndrome produces anticardiolipin antibodies, these patients test "positive" for syphilis even though they DON'T have syphilis. This is called a false positive.

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"Lupus anticoagulant can cause prolonged PTT that is not corrected by the addition of normal platelet-free plasma"

• PTT (Partial Thromboplastin Time) = a lab test measuring how quickly blood clots via the intrinsic clotting pathway.
• Lupus anticoagulant interferes with this test and PROLONGS it.
• Not corrected by mixing = normally, if a clotting factor is deficient (like hemophilia), mixing the patient's blood with normal blood (which has the factor) will correct the PTT. But lupus anticoagulant is an INHIBITOR (an antibody), so adding normal plasma doesn't fix it because the antibody is still present and still inhibiting.

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"Treatment: systemic anticoagulation"

• Blood thinners (heparin, then warfarin) to prevent blood clots. Long-term anticoagulation is required.

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PAGE 5 - POLYMYALGIA RHEUMATICA, FIBROMYALGIA, POLYMYOSITIS, DERMATOMYOSITIS, MYOSITIS OSSIFICANS, IgG4-RELATED DISEASE

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POLYMYALGIA RHEUMATICA (PMR)

"Pain and stiffness in proximal muscles (eg, shoulders, hips), often with fever, malaise, weight loss"

• Proximal muscles = muscles closest to the body's center - shoulders, upper arms, hips, thighs. Think: the muscles you use to raise your arm above your head or get up from a chair.
• These areas become stiff and achy - especially in the morning.
• Patients often say they can't brush their hair or raise their arm.

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"Does not cause muscular weakness"

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"More common in females ≥ 50 years old; associated with giant cell (temporal) arteritis"

• PMR almost exclusively affects people over 50. Under 50 = look for another diagnosis.
• Giant cell (temporal) arteritis = inflammation of large blood vessels, especially the temporal artery in the scalp. 10-15% of PMR patients also have GCA. The two diseases overlap strongly.

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"↑ ESR, ↑ CRP, normal CK"

• Elevated ESR and CRP = active inflammation markers (as explained above).
• Normal CK = Creatine Kinase is a muscle enzyme. When muscles are DAMAGED (as in myositis), CK leaks out and elevates. In PMR, muscles hurt but are NOT damaged → CK is normal. This again distinguishes PMR from myositis.

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"Rapid response to low-dose glucocorticoids"

• PMR responds DRAMATICALLY to even small doses of prednisone (steroids). Patients feel better within 24-48 hours. This rapid response to steroids is itself almost diagnostic of PMR.

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FIBROMYALGIA

"Most common in females 20-50 years old. Chronic, widespread musculoskeletal pain associated with 'tender points,' stiffness, paresthesias, poor sleep, fatigue, cognitive disturbance ('fibro fog')"

• Fibro = fibers (muscles, tendons), myalgia = pain. So: widespread muscle/fiber pain.
• Tender points = specific anatomical spots that are exquisitely tender when pressed. There are 18 classic tender point locations.
• Paresthesias = abnormal sensations like tingling, burning, or "pins and needles."
• Fibro fog = cognitive difficulties - poor concentration, memory problems, mental cloudiness. Patients feel like they're "thinking through fog."

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"Normal inflammatory markers like ESR. Treatment: regular exercise, antidepressants (TCAs, SNRIs), neuropathic pain agents (eg, gabapentinoids)"

• Normal ESR = NO inflammation! This is critical. Fibromyalgia is NOT an inflammatory or autoimmune disease. Pain exists without tissue damage or inflammation.
• TCAs (tricyclic antidepressants like amitriptyline) and SNRIs (duloxetine) = treat the central pain sensitization in fibromyalgia.
• Gabapentinoids (pregabalin, gabapentin) = drugs that dampen abnormal nerve firing, reducing pain signals.
• Exercise is ESSENTIAL - it improves pain, fatigue, and sleep.

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POLYMYOSITIS / DERMATOMYOSITIS

"Nonspecific: ⊕ ANA, ↑ CK. Specific: ⊕ anti-Jo-1 (histidyl-tRNA synthetase), ⊕ anti-SRP (signal recognition particle), ⊕ anti-Mi-2 (helicase)"

• ⊕ ANA = positive antinuclear antibodies (general autoimmune marker).
• ↑ CK = elevated Creatine Kinase = actual muscle DAMAGE is occurring (unlike PMR!). Muscle cells are being destroyed by the immune system, and CK leaks out.
• Anti-Jo-1 = the most important specific antibody. Jo-1 targets histidyl-tRNA synthetase, an enzyme involved in making proteins. Associated with interstitial lung disease (lung scarring) + myositis + arthritis.
• Anti-SRP = antibody against signal recognition particle (a cellular protein). More aggressive disease.
• Anti-Mi-2 = antibody against helicase (a DNA-unwinding enzyme). Associated with dermatomyositis specifically.

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POLYMYOSITIS

"Progressive symmetric proximal muscle weakness, characterized by endomysial inflammation with CD8+ T cells. Most often involves shoulders."

• Progressive = gets worse over time.
• Symmetric = BOTH sides equally weak. Can't raise BOTH arms.
• Proximal = shoulders, hips. Patients struggle to stand from sitting, raise arms overhead, climb stairs.
• Endomysial = the inflammation is IN the muscle fibers themselves (endo = within, mysial = muscle).
• CD8+ T cells = cytotoxic (killer) T cells. These are immune cells that directly kill muscle fibers. (Compare to dermatomyositis where CD4+ T cells and B cells are more involved.)

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DERMATOMYOSITIS

"Clinically similar to polymyositis, but also involves Gottron papules, photodistributed facial erythema (heliotrope [violaceous] edema of the eyelids), 'shawl and face' rash, mechanic's hands, ↑ risk of occult malignancy"

• Dermatomyositis = DERMO (skin) + myositis (muscle inflammation). So both skin AND muscles affected.
• Gottron papules = reddish/purple flat-topped bumps over the knuckles (over the DIP and PIP joints). Very characteristic.
• Photodistributed = the rash occurs in sun-exposed areas.
• Heliotrope rash = a violet/purple discoloration around the eyelids. "Heliotrope" is a purple flower. The eyelids look like they have a purple shadow.
• Shawl sign = erythema (redness) over the upper back, shoulders, and upper arms - in the distribution of a shawl/cape.
• Mechanic's hands = rough, cracked, thickened skin on the fingers and palms (as if the patient does manual labor). Caused by hyperkeratosis (skin thickening).
• ↑ risk of occult malignancy = hidden cancer. Dermatomyositis can be a paraneoplastic syndrome (a manifestation of an underlying cancer). Must screen for cancer in all dermatomyositis patients. Most common associated cancers: ovarian, lung, GI, breast.
• Perimysial inflammation with CD4+ T cells = the inflammation is AROUND muscle fiber bundles (perimysium), involving CD4+ helper T cells and B cells (different from polymyositis).

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MYOSITIS OSSIFICANS

"Heterotopic ossification involving skeletal muscle (eg, quadriceps). Associated with blunt muscle trauma."

• Heterotopic = occurring in an abnormal location (hetero = other, topic = place).
• Ossification = bone formation.
• So: bone forming INSIDE a muscle! After blunt trauma (like a football tackle to the thigh), the damaged muscle heals by turning into bone instead of normal muscle tissue.
• Presents as a painful, hard mass in the muscle weeks after injury.

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"Imaging: eggshell calcification. Histology: metaplastic bone surrounding area of fibroblastic proliferation. Benign, but may be mistaken for sarcoma."

• Eggshell calcification = on X-ray, the ossification has a peripheral shell of dense bone (like an eggshell) with immature bone inside.
• Metaplastic bone = bone that formed from non-bone cells (meta = change, plastic = form). Muscle cells became bone cells.
• Sarcoma = bone/soft tissue cancer. Myositis ossificans can look scary on imaging and biopsy, but it is BENIGN.

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IgG4-RELATED DISEASE

"Immune-mediated spectrum of conditions, characterized by fibrosis and lymphoplasmacytic infiltrate, that can affect multiple organs. Patients usually have elevated serum IgG4 levels."

• IgG4 = a subtype of immunoglobulin G (a type of antibody). When overproduced, IgG4 infiltrates various organs and causes fibrosis.
• Fibrosis = scar tissue formation within organs.
• Lymphoplasmacytic infiltrate = lymphocytes and plasma cells (both types of white blood cells) invading the organ tissue.

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Most common IgG4-related conditions:

• Sialadenitis and dacryoadenitis = inflammation of salivary glands and lacrimal (tear) glands. Very similar presentation to Sjögren syndrome but mechanism differs.
• Riedel thyroiditis = fibrosis of the thyroid gland, causing it to become hard as rock. Can compress the trachea.
• Autoimmune pancreatitis = the pancreas becomes inflamed by IgG4 infiltration. Looks like pancreatic cancer on imaging (important to distinguish!).
• Autoimmune aortitis = inflammation of the aorta (the body's largest artery). Can lead to TAA (Thoracic Aortic Aneurysm) or AAA (Abdominal Aortic Aneurysm) - dangerous bulging of the aorta.
• Retroperitoneal fibrosis = fibrosis behind the abdominal cavity that can wrap around the ureters (tubes from kidneys to bladder) → blocking urine flow → hydronephrosis (kidney swelling) → CKD (chronic kidney disease).

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PAGE 6 - VASCULITIDES

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WHAT IS VASCULITIS?

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LARGE-VESSEL VASCULITIS

GIANT CELL (TEMPORAL) ARTERITIS

• Unilateral headache = one-sided headache, often over the temple (the area beside your eye near the scalp).
• Jaw claudication = pain in the jaw when chewing because the inflamed temporal artery can't deliver enough blood to the chewing muscles during activity. "Claudication" = cramping pain during exertion due to inadequate blood flow.
• Temporal artery tenderness = the temporal artery on the scalp is tender to touch.
• Blindness risk = the temporal artery also supplies the ophthalmic artery → optic nerve → eye. Inflammation can occlude this → sudden blindness.
• Granulomatous inflammation = the blood vessel wall is infiltrated by macrophages that form granulomas (nodules of immune cells).
• Affects temporal, vertebral, and ophthalmic arteries.

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TAKAYASU ARTERITIS

• "Pulseless disease" = the inflammation affects the aorta and its major branches (subclavian, carotid, vertebral arteries). When these narrow from inflammation, you can't feel the pulse in the arms.
• Weak upper extremity pulses = same reason.
• Fever, night sweats, arthritis, myalgias = systemic inflammation symptoms.
• Narrowing of aortic arch and proximal great vessels = on imaging you see stenosis (narrowing) of the aorta.

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MEDIUM-VESSEL VASCULITIS

BUERGER DISEASE (Thromboangiitis Obliterans)

• Leading to intermittent claudication, risk of gangrene.
• Raynaud phenomenon = fingers/toes turn white then blue then red in response to cold/stress.
• Autoamputation of digits = the blood vessels to fingers/toes are obliterated by clotting → tissue dies → digits fall off!
• Superficial nodular phlebitis = inflammatory nodules along superficial veins.

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KAWASAKI DISEASE

• Conjunctivitis (bilateral non-exudative - red eyes without discharge)
• Rash (polymorphous - different types)
• Adenopathy (cervical - swollen neck lymph nodes)
• Strawberry tongue (bright red tongue)
• Hand-foot changes - edema (swelling), redness.
• Fever ≥ 5 days = fever lasting at least 5 days is required for diagnosis.

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POLYARTERITIS NODOSA (PAN)

• Fever, weight loss, abdominal pain, melena (blood in stool)
• Hypertension, neurologic dysfunction, cutaneous eruptions, renal damage
• Involves renal and visceral vessels (arteries to intestines, kidneys, muscles).
• Transmural inflammation = inflammation through the FULL thickness of the vessel wall.
• Fibrinoid necrosis = the vessel wall dies and is replaced by eosinophilic fibrin-like material.

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SMALL-VESSEL VASCULITIS (MPO-ANCA / p-ANCA)

MICROSCOPIC POLYANGIITIS

• Necrotizing vasculitis involving lungs, kidneys, and skin.
• Pauci-immune glomerulonephritis (GN) = inflammation of kidney glomeruli with very few immune deposits ("pauci" = few). The damage is mostly from the ANCA antibodies directly, not immune complex deposition.
• Palpable purpura = small hemorrhagic (blood-leaking) lesions that you can FEEL (palpable) because they are inflamed - this distinguishes vasculitic purpura from other types.

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EOSINOPHILIC GRANULOMATOSIS WITH POLYANGIITIS (EGPA)

• Combination of ASTHMA + eosinophilia + systemic vasculitis = the classic triad.
• Granulomatous, necrotizing vasculitis with eosinophils = the vessel wall inflammation contains eosinophils (a type of white blood cell usually associated with allergies and parasites).
• Eosinophilic infiltration → inflammation → peripheral neuropathy = eosinophils damage nerves.
• ↑ IgE level = the allergic/eosinophilic nature raises IgE antibody levels.
• MPO-ANCA/p-ANCA positive.

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PAGE 7 - MORE VASCULITIDES (Granulomatosis with Polyangiitis, Cryoglobulinemia, Behçet Syndrome, IgA Vasculitis)

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GRANULOMATOSIS WITH POLYANGIITIS (GPA) (PR3-ANCA / c-ANCA)

• Sinusitis, otitis media, rhinitis, hemoptysis (coughing blood), lower respiratory involvement.
• Saddle-nose deformity = the chronic inflammation destroys the nasal cartilage → the nose collapses in the middle, creating a saddle-shaped depression.
• Rapidly progressive GN (glomerulonephritis) → if untreated, quickly destroys kidneys.

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MIXED CRYOGLOBULINEMIA / CRYOGLOBULIN VASCULITIS

• Purpura, arthralgia, weakness, neuropathy, and renal disease (eg, GN), ocular manifestations.
• Triad: palpable purpura, arthralgia, renal involvement (stomach pain, arthralgia intussusception, palpable purpura on buttocks/legs).
• Palpable purpura NO visceral involvement = can have skin-only disease.

• Cryoglobulins = immunoglobulins (antibodies) that precipitate (crystallize) in the cold and dissolve back at body temperature. They clog small vessels when cold.
• Vasculitis 2° to IgA immune complex deposition = late involvement indicates systemic disease.

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IgA VASCULITIS (Henoch-Schönlein Purpura - HSP)

1. Palpable purpura on buttocks/legs (in a dependent distribution - gravity dependent areas)
2. Arthralgia = joint pain
3. Abdominal pain (can cause intussusception - bowel telescoping)
4. Renal disease (IgA nephropathy)

• IgA immune complexes deposit in small vessel walls (skin, kidneys, GI tract, joints).
• Henoch-Schönlein purpura is essentially IgA nephropathy (Berger disease) + systemic vasculitis.

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BEHÇET SYNDROME

• Recurrent oral and genital ulcers = painful sores in mouth AND genital area. This combo is a hallmark.
• Uveitis = eye inflammation → can cause blindness.
• Erythema nodosum = painful red nodules under the skin (especially on shins) - a type of panniculitis (fat layer inflammation).
• Triggered by HSV or parvovirus. Flares last 1-4 weeks.

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PAGE 8 - NEUROMUSCULAR JUNCTION DISEASES & RAYNAUD PHENOMENON

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MYASTHENIA GRAVIS (MG)

"Most common NMJ disorder"

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"Autoantibodies to postsynaptic ACh receptor → ↓ ACh release"

• These antibodies BLOCK the receptor so acetylcholine can't bind.
• They also DESTROY receptors over time.
• Result: muscle doesn't receive the signal to contract → WEAKNESS.

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Clinical features:

• Fatigable = weakness gets WORSE with repeated use or activity. The muscle is fine at rest but weakens quickly with use. This is the hallmark. (Opposite of Lambert-Eaton where strength briefly IMPROVES with repeated use.)
• Ptosis = drooping of the eyelids (the eyelid muscles are among the first affected).
• Diplopia = double vision (extraocular eye muscles affected).
• Respiratory muscles → breathing difficulty (myasthenic crisis = life-threatening).
• Bulbar muscles = muscles of the throat/palate used for swallowing and chewing.
• Dysphagia = difficulty swallowing.

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"Spared reflexes"

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"Worsens with muscle use"

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"Associated with thymoma, thymic hyperplasia"

• The thymus gland (behind the breastbone) plays a key role in MG.
• Thymoma = tumor of the thymus. Found in ~15% of MG patients.
• Thymic hyperplasia = enlarged thymus. Found in ~65% of MG patients.
• The thymus is where the autoreactive T cells that drive the antibody response are thought to originate.
• Thymectomy (surgical removal of thymus) can improve MG!

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"ACh inhibitor administration - Reverses symptoms (pyridostigmine for treatment)"

• Pyridostigmine = an acetylcholinesterase inhibitor. Acetylcholinesterase is the enzyme that breaks down ACh in the synapse.
• Blocking this enzyme = ACh lasts longer in the synapse = can overcome the blocked receptors = muscle gets the signal = temporary improvement in strength.
• This is the mainstay of symptomatic treatment.

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LAMBERT-EATON MYASTHENIC SYNDROME (LEMS)

"Uncommon. Autoantibodies to presynaptic Ca²⁺ channels → ↓ ACh release"

• The antibodies here are against presynaptic voltage-gated calcium channels on the NERVE side (presynaptic).
• Calcium entering through these channels is what TRIGGERS ACh release from the nerve.
• Block calcium channels → less ACh released → less muscle stimulation → weakness.

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"Proximal muscle weakness, autonomic symptoms (dry mouth, constipation, impotence)"

• Autonomic = the automatic nervous system (controls involuntary functions). LEMS affects both somatic (voluntary muscles) and autonomic nerves.
• Dry mouth = less saliva from reduced ACh on salivary glands.
• Constipation = reduced gut motility.
• Impotence = erectile dysfunction.

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"Hyporeflexia. Improves with muscle use"

• Hyporeflexia = reduced reflexes (because less ACh is being released throughout).
• Improves with repeated muscle use = the OPPOSITE of MG! With repeated activity, calcium builds up in the presynaptic terminal → more ACh release → brief improvement in strength. This is the key distinguishing feature from MG.

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"Small cell lung cancer"

• LEMS is a paraneoplastic syndrome - often a sign of underlying small cell lung cancer.
• The cancer cells (which come from neuroendocrine tissue) express voltage-gated calcium channels.
• The immune system makes antibodies against the cancer → these same antibodies cross-react with normal neuromuscular junction calcium channels.

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"ACh inhibitor administration - Minimal effect"

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THE DIAGRAM COMPARISON: MG vs LEMS

• In MG: Antibodies block the ACh receptor on the muscle side (postsynaptic). ACh is released but can't bind its target.
• In LEMS: Antibodies block Ca²⁺ channels on the nerve side (presynaptic). Ca²⁺ can't enter → ACh can't be released → muscle doesn't receive signal.

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RAYNAUD PHENOMENON

"↓ blood flow to skin due to arteriolar (small vessel) vasospasm in response to cold or stress. Color change from white (ischemia) to blue (hypoxia) to red (reperfusion)."

• Arteriolar vasospasm = the tiny blood vessels that feed the fingers/toes suddenly CLAMP SHUT (spasm) in response to cold or emotional stress.
• This is exaggerated sympathetic nervous system response.

1. White (pallor/ischemia) = vessels clamp shut → no blood → white, cold fingers.
2. Blue (cyanosis/hypoxia) = the little blood remaining loses its oxygen → turns blue/purple.
3. Red (hyperemia/reperfusion) = vessels relax, blood rushes back in → bright red, burning sensation.

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"Most often in the fingers and toes. Called Raynaud disease when 1° (idiopathic), Raynaud syndrome when 2° to a disease process such as mixed connective tissue disease, SLE, or CREST syndrome (limited form of systemic sclerosis)."

• Raynaud disease (primary) = occurs on its own, no underlying disease. Benign, mainly a nuisance.
• Raynaud syndrome (secondary) = occurs as part of another disease (scleroderma, SLE, MCTD, RA). More severe and dangerous.

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"Digital ulceration (critical ischemia). Treat with calcium channel blockers."

• In severe secondary Raynaud, the repeated vasospasm leads to permanent tissue damage → open sores (ulcers) at the fingertips.
• Calcium channel blockers (like nifedipine) = relax blood vessel walls by blocking calcium entry into vascular smooth muscle → vessels dilate → better blood flow.

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SUMMARY TABLE - KEY DISTINCTIONS TO REMEMBER

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