---

COMPLETE LECTURE EXPLANATION - Pages 490 to 498

---

PAGE 490 - OTHER BLISTERING SKIN DISORDERS

---

1. DERMATITIS HERPETIFORMIS

"Pruritic papules, vesicles, and bullae (often found on elbows, knees, buttocks)"

• Pruritic = Itchy. This is one of the most itchy skin conditions you can imagine. Patients scratch intensely.
• Papules = Small, solid, raised bumps on the skin (like a pimple but not filled with pus). Think of a mosquito bite bump.
• Vesicles = Small blisters filled with clear fluid. Like tiny water bubbles on the skin.
• Bullae = Large blisters - same as vesicles but bigger (> 5 mm in diameter). Think of a large blister you get after a bad burn.
• Why elbows, knees, buttocks? These are extensor surfaces - areas that stick out and get friction. The IgA deposits (antibodies from the immune system) tend to cluster here.

"Deposits of IgA at tips of dermal papillae"

• IgA = A type of antibody (a protein your immune system makes to fight things). Normally IgA protects your gut lining. But in this disease, IgA goes rogue and attacks the skin.
• Dermal papillae = Tiny finger-like projections at the junction between the epidermis (outer skin) and dermis (inner skin). Think of them like the bumpy underside of a stamp that interdigitates with the paper.
• Why this matters: When IgA deposits at these tips, it triggers inflammation and causes the skin to blister. This is actually how you DIAGNOSE this disease - by doing a skin biopsy and looking for these IgA deposits with a special immunofluorescence test.

"Associated with celiac disease"

• Celiac disease = An autoimmune condition where eating gluten (a protein in wheat, barley, rye) damages the small intestine. The same antibodies (anti-tissue transglutaminase IgA) that attack the gut lining also attack the skin.
• Think of it this way: The gut and the skin are both under attack by the same immune system gone wrong.

"Treatment: dapsone, gluten-free diet"

• Dapsone = An antibiotic (originally used for leprosy) that also has anti-inflammatory properties. It quickly relieves the itching and blistering - but it does NOT fix the underlying gut disease.
• Gluten-free diet = The actual cure for both the gut and skin disease. It takes months to work on the skin, but it fixes the root cause.
• Why both? Dapsone for fast symptom relief, gluten-free diet for long-term cure.

---

2. ERYTHEMA MULTIFORME

"Associated with infections (eg, Mycoplasma pneumoniae, HSV), drugs (eg, sulfa drugs, β-lactams, phenytoin)"

• Erythema = Redness of the skin (from the Greek "erythros" = red).
• Multiforme = Multiple forms - meaning this disease shows MANY different types of skin lesions at the same time (that's the key feature).
• Mycoplasma pneumoniae = A bacterium that causes "walking pneumonia" - a mild lung infection where the patient doesn't feel sick enough to stay in bed but has a persistent cough.
• HSV = Herpes Simplex Virus - the virus that causes cold sores (HSV-1) or genital herpes (HSV-2). It is the MOST COMMON trigger of erythema multiforme. Every time HSV reactivates, it can trigger a new episode.
• Sulfa drugs = Antibiotics like sulfamethoxazole (the "sulfa" in Bactrim/TMP-SMX). These are common drug triggers.
• β-lactams = A class of antibiotics that includes penicillin, amoxicillin, cephalosporins. The "beta-lactam ring" in their structure is what gives them their name.
• Phenytoin = An anti-seizure (anti-epileptic) drug. One of the most notorious drug triggers for skin reactions.
• Why do infections and drugs cause this? The immune system overreacts to the infection or drug and mistakenly attacks the skin cells in a type IV hypersensitivity (delayed, T-cell mediated) reaction.

"Presents with multiple types of lesions - macules, papules, vesicles, target lesions (look like targets with multiple rings and dusky center showing epithelial disruption)"

• Macules = Flat spots of color change (like a freckle). You cannot feel them - they are just color changes.
• Papules = Raised solid bumps (as explained above).
• Vesicles = Small fluid-filled blisters.
• Target lesions = THE HALLMARK of erythema multiforme. They look exactly like a shooting target or a bull's-eye:
  • Outer ring = red/pink
  • Middle ring = paler/lighter
  • Center = dark/dusky (because the skin cells are dying = "epithelial disruption")
  • This 3-zone pattern is diagnostic!
• Why "multiforme" (multiple forms)? Because ALL of these different lesion types appear on the same patient at the same time - macules, papules, vesicles, AND target lesions.

---

3. STEVENS-JOHNSON SYNDROME (SJS)

"Characterized by fever, bullae formation and necrosis, sloughing of skin at dermal-epidermal junction (⊕ Nikolsky), high mortality rate"

• Fever = This is a SYSTEMIC disease - it affects the whole body, not just the skin. The patient is very sick.
• Bullae formation = Large blisters form on the skin.
• Necrosis = Cell death. The skin cells are literally dying.
• Sloughing = The skin peels off in sheets, like wet wallpaper coming off a wall. This is horrifying to see.
• Dermal-epidermal junction = The border between the outer skin (epidermis) and the inner skin (dermis). In SJS, the split (separation) happens at this exact layer.
• ⊕ Nikolsky sign = A positive Nikolsky sign means: when you gently rub the skin sideways with your finger, the top layer (epidermis) slides off, like pushing wet tissue paper. This tells you the skin layers are NOT properly attached - they are separating. Named after Dr. Pyotr Nikolsky who described it. This is a sign of a SERIOUS blistering disease.
• High mortality rate = People die from this disease. Why? Because when skin is gone, you lose:
  • Protection from infection (sepsis is the #1 killer)
  • Fluid control (patients lose massive amounts of fluid, like burn patients)
  • Temperature regulation

"Typically mucous membranes are involved"

• Mucous membranes = The wet linings of body openings - mouth, eyes (conjunctiva), genitals, anus. In SJS, these are attacked too. Patients have painful oral ulcers (can't eat), eye involvement (can cause blindness), and genital ulcers.

"Targetoid skin lesions may appear, as seen in erythema multiforme"

• SJS is actually considered a SEVERE end of the erythema multiforme spectrum by some experts. It can show similar target-like lesions.

"Usually associated with adverse drug reaction"

• The most common causes: sulfonamides (Bactrim), anti-epileptics (phenytoin, carbamazepine, lamotrigine), allopurinol, NSAIDs.
• Unlike erythema multiforme (which is often from infections), SJS is almost always DRUG-CAUSED.

"Toxic epidermal necrolysis (TEN) is more severe form of SJS involving > 30% body surface area. 10-30% involvement denotes SJS-TEN."

• Toxic Epidermal Necrolysis (TEN) = The most severe form. "Toxic" = poisonous to the body, "epidermal" = outer skin, "necrolysis" = destruction of cells (lysis = breaking apart).
• Think of it as a spectrum:
  • Erythema multiforme = Mild (< 10% body surface affected)
  • SJS = Moderate (< 10% body surface, but mucous membranes involved)
  • SJS-TEN overlap = 10-30% body surface
  • TEN = Severe (> 30% body surface) - essentially the entire skin falls off
• Mortality of TEN can be 30-40%. Patients are treated like burn patients in an ICU.

---

4. INHERITED EPIDERMOLYSIS BULLOSA

"Group of inherited skin disorders characterized by bullae, erosions, and ulcers triggered by minor trauma"

• Inherited = You are born with a gene mutation that causes this - it runs in families.
• Epidermolysis = "Lysis (breaking apart) of the epidermis" - the outer skin layers separate easily.
• Bullosa = Blistering.
• Minor trauma = Even touching the skin gently, wearing shoes, or drinking from a bottle can cause blisters. The skin is extraordinarily fragile.

"Presents with blisters early in life and oral blisters with bottle feeding"

• Newborn babies get blisters just from the suction pressure of drinking from a bottle. This is often how the disease is first noticed.

"Most commonly caused by mutations in keratin genes"

• Keratin = A strong structural protein that gives skin (and nails, hair) their toughness. Think of it as the "rebar" inside the concrete of your skin.
• When keratin genes are mutated, the keratin protein is defective or absent, so the skin layers cannot hold together under even gentle force.
• There are different subtypes (simplex, junctional, dystrophic) depending on which specific protein is affected and which layer splits.

---

PAGE 491 - CUTANEOUS ULCERS (Comparison Table)

---

VENOUS ULCER

"Chronic venous insufficiency; most common ulcer type"

• Venous insufficiency = The veins in the leg are not properly pumping blood back up to the heart. The valves inside the veins are broken, so blood pools (stagnates) in the legs.
• This is the MOST COMMON type of leg ulcer - about 70% of all leg ulcers.

"Gaiter area (ankle to midcalf), typically over malleoli"

• Gaiter area = The area of the leg covered by a gaiter (a sock-like covering) - from the ankle to mid-calf. This is where blood pressure in the veins is highest.
• Malleoli = The bony bumps on either side of your ankle (medial malleolus = inner bump, lateral malleolus = outer bump). These are classic sites.

"Irregular border, shallow, exudative"

• Irregular border = The edges of the ulcer are ragged and uneven (unlike arterial ulcers which are very sharply defined).
• Shallow = The ulcer doesn't go deep.
• Exudative = It oozes/weeps fluid. Because of the increased venous pressure, plasma leaks out of capillaries.

"Mild to moderate (pain)"

• Venous ulcers are not as painful as arterial ulcers. The pain improves when you ELEVATE the leg (because gravity helps drain the pooled blood).

Associated signs: "Telangiectasias, varicose veins, edema, stasis dermatitis (erythematous eczematous patches)"

• Telangiectasias = Dilated, visible small blood vessels on the skin surface - look like little red spider veins.
• Varicose veins = Enlarged, twisted, bulging veins visible under the skin - caused by the broken valves.
• Edema = Swelling from fluid accumulation.
• Stasis dermatitis = "Stasis" = stagnant. The pooled blood causes inflammation of the skin, leading to redness, eczema-like rash, and brownish discoloration (from hemosiderin deposits - iron from broken-down red blood cells).

---

ARTERIAL ULCER

"Peripheral artery disease (eg, atherosclerotic stenosis)"

• Peripheral artery disease (PAD) = The arteries supplying the legs become narrowed by fatty plaques (atherosclerosis). Less blood = less oxygen to the tissue = tissue dies = ulcer.
• Atherosclerotic stenosis = "Atherosclerosis" = hardening and narrowing of arteries by fatty deposits. "Stenosis" = narrowing.
• Think of it like a garden hose with a kink in it - not enough water gets through.

"Distal toes, anterior shin, pressure points"

• Distal toes = The tips of the toes - farthest from the heart, so they get the least blood flow.
• Anterior shin = The bony front of the lower leg - little cushioning, poor blood supply.
• These are the areas where blood supply is lowest, so they die first.

"Symmetric with well-defined punched-out appearance"

• Well-defined punched-out = The edges are sharp and clean, like someone punched a hole in the skin with a hole-puncher. This is very different from the ragged edges of venous ulcers.

"Severe (pain)"

• Arterial ulcers are EXTREMELY painful. Pain worsens when you ELEVATE the leg (because gravity can no longer help even the tiny trickle of blood reach the foot). Pain improves when you DANGLE the leg (letting gravity help fill the arteries). This is called "dependent rubor" - the foot turns red when dangled.

Associated signs: "Arterial insufficiency, cold and pale atrophic skin, hair loss, absent pulses"

• Cold and pale = No warm arterial blood reaching the skin.
• Atrophic skin = Thin, shiny skin without hair or texture - from chronic poor blood supply.
• Hair loss = Hair follicles need blood supply to grow. No blood = no hair.
• Absent pulses = You cannot feel the dorsalis pedis or posterior tibial pulse in the foot - the artery is blocked.

---

NEUROPATHIC ULCER

"Peripheral neuropathy (eg, diabetic foot)"

• Neuropathy = Nerve damage. In diabetes, high blood sugar damages nerve fibers, especially the small sensory nerves in the feet.
• When you cannot FEEL pain, you don't notice injuries. You keep walking on a wound, it gets deeper, and it ulcerates.

"Bony prominences (eg, metatarsal heads, heel)"

• Metatarsal heads = The "balls" of your feet - the round knobby parts at the base of your toes where pressure is highest when walking.
• These are pressure points. Without pain sensation, the patient doesn't shift weight, so constant pressure causes tissue death.

"Hyperkeratotic edge with undermined borders"

• Hyperkeratotic = Thickened, hard, calloused skin around the ulcer edge (from repetitive trauma without pain response).
• Undermined borders = The ulcer tunnels under the skin edge - the hole is larger underneath than what you see on the surface.

"Absent (pain)"

• The ulcer is PAINLESS - this is what makes it so dangerous. The patient literally cannot feel it getting worse.

Associated signs: "Claw toes, Charcot joints, absent reflexes"

• Claw toes = Toes curled like claws - caused by muscle imbalance from nerve damage.
• Charcot joints = Neuropathic arthropathy - the joints in the foot collapse and deform (like a "bag of bones") because the patient keeps bearing weight on a damaged joint without pain feedback.
• Absent reflexes = In a normal exam, tapping the Achilles tendon gives a reflex kick. In neuropathy, this reflex is lost.

---

PRESSURE INJURY (Pressure Ulcer / Bedsore)

"Prolonged unrelieved pressure (eg, immobility)"

• When a patient lies in one position for too long (coma, paralysis, post-surgical), the skin between the bone and the bed surface gets crushed. The blood supply is cut off, the tissue dies.

"Varies based on stage from non-blanchable erythema to full-thickness skin loss"

• Stage 1 = Redness that does not blanch (turn white) when pressed. The skin is intact.
• Stage 2 = Partial thickness - blisters, shallow open wound.
• Stage 3 = Full thickness - crater going into fat but not through to bone.
• Stage 4 = Down to muscle, tendon, or bone.
• Unstageable = Cannot see the base because of dead tissue (eschar) covering it.

"Soft tissue infection and osteomyelitis are frequent complications"

• Osteomyelitis = Infection of the bone ("osteo" = bone, "myel" = marrow, "itis" = inflammation/infection). Once the ulcer reaches bone, bacteria invade the bone, and this is very hard to treat.

---

PAGE 492 - MISCELLANEOUS SKIN DISORDERS

---

ACANTHOSIS NIGRICANS

"Epidermal hyperplasia causing symmetric, hyperpigmented thickening of skin, especially in neck, axilla, or on neck"

• Epidermal hyperplasia = Overgrowth ("hyper" = too much, "plasia" = growth) of the outer skin cells.
• Hyperpigmented = Darkening of the skin - looks brown to black, velvety.
• Axilla = Armpit.
• Classic description: Dark, velvety, thickened skin in the neck creases and armpits. People sometimes think it's dirt that won't wash off.

"Associated with insulin resistance (eg, diabetes, obesity, Cushing syndrome, PCOS), visceral malignancy (eg, gastric adenocarcinoma)"

• Insulin resistance = Your body makes insulin but the cells don't respond to it properly, so the pancreas makes MORE insulin. This high insulin level stimulates skin cell receptors (IGF-1 receptors), causing overgrowth.
• PCOS = Polycystic Ovary Syndrome - a hormonal condition in women with insulin resistance.
• Cushing syndrome = Excess cortisol (stress hormone) - causes insulin resistance.
• Visceral malignancy = Cancer of internal organs - especially stomach cancer. When acanthosis nigricans appears suddenly in a thin person with no known metabolic disease, it is a RED FLAG for internal cancer (paraneoplastic syndrome).

---

ERYTHEMA NODOSUM

"Painful, raised inflammatory lesions of subcutaneous fat (panniculitis), usually on anterior shins"

• Panniculitis = Inflammation of the subcutaneous fat ("panniculus" = layer of fat under the skin). This fat layer is called the "hypodermis."
• Anterior shins = Front of the lower legs - most common location.
• Lesions appear as painful, tender, red/purple bumps under the skin. You can feel them but the overlying skin looks relatively normal initially.

"Often idiopathic, but can be associated with sarcoidosis, coccidioidomycosis, histoplasmosis, TB, streptococcal infections, leprosy, inflammatory bowel disease"

• Idiopathic = No identifiable cause (the most common category!).
• Sarcoidosis = A disease where the immune system forms granulomas (tiny clumps of immune cells) in various organs.
• Coccidioidomycosis / Histoplasmosis = Fungal infections endemic to certain regions (southwestern US, Ohio River Valley respectively).
• TB = Tuberculosis.
• Think of erythema nodosum as a "reactive" condition - the body's immune system is overreacting to something (infection, inflammation) and creates painful fat inflammation.

---

ICHTHYOSIS VULGARIS

"Disorder of defective keratinocyte desquamation due to filaggrin gene mutations resulting in diffuse scaling of the skin, most commonly on the extensor surface of extremities and the trunk"

• Ichthyosis = From "ichthys" (Greek for fish) - because the skin looks and feels like fish scales.
• Vulgaris = Common - this is the most common inherited skin disorder.
• Keratinocytes = The main skin cells of the epidermis. They produce keratin.
• Desquamation = Normal shedding of dead skin cells. We all shed millions of skin cells daily. In ichthyosis, this shedding is defective - the dead cells pile up instead of falling off.
• Filaggrin = "Filament aggregating protein" - a protein that helps glue the keratin filaments together and helps the skin barrier work. Without it, the skin can't shed properly and the skin barrier is weakened.
• Extensor surfaces = Back of arms, front of legs - the outer-facing surfaces.

"Manifests in infancy or early childhood. Strong association with atopic dermatitis"

• Atopic dermatitis = Eczema - the itchy, dry, inflamed skin condition. Both share the same filaggrin deficiency, causing a leaky skin barrier that triggers inflammation.

---

LICHEN PLANUS

"Pruritic, purple, polygonal planar papules and plaques are the 6 P's of Lichen Planus"

• This is a classic exam mnemonic - THE 6 P's:
  1. Pruritic = Itchy
  2. Purple = Color of the lesions (violaceous)
  3. Polygonal = Many-angled - not round, but has multiple flat sides
  4. Planar = Flat-topped (not domed)
  5. Papules = Raised bumps
  6. Plaques = Larger flat raised areas

"Mucosal involvement manifests as Wickham striae (reticular white lines and hypergranulosis)"

• Mucosal involvement = Inside the mouth or genitals are affected.
• Wickham striae = Fine, lacy white lines on the surface of oral lesions. Named after Dr. Wickham who first described them. This is pathognomonic (uniquely specific) for lichen planus.
• Hypergranulosis = Thickening of the granular cell layer in the skin - seen on microscopy.

"Sawtooth infiltrate of lymphocytes at dermal-epidermal junction"

• Sawtooth pattern = On biopsy, the rete ridges (the downward projections of epidermis into dermis) take on an irregular sawtooth/pointed shape.
• Lymphocyte infiltrate = Immune cells (lymphocytes = white blood cells) pile up at the border of epidermis and dermis, attacking the skin cells.
• This is the histological (microscope) signature of lichen planus.

"Associated with hepatitis C"

• Hepatitis C virus somehow triggers an autoimmune response that leads to lichen planus. Always screen for Hep C in lichen planus patients.

---

PITYRIASIS ROSEA

"Herald patch followed days later by other scaly erythematous plaques, often in a 'Christmas tree' distribution on trunk"

• Pityriasis = Scaly skin condition.
• Rosea = Pink/rosy colored.
• Herald patch = THE FIRST LESION - a single, larger oval, scaly pink patch that appears days to weeks BEFORE the rest of the rash. "Herald" = announces something coming. It's like the announcement of the army before the army arrives.
• Christmas tree distribution = The subsequent smaller patches follow the lines on the back in a pattern that resembles a Christmas tree. Why? Because they follow "Langer's lines" (tension lines of the skin) on the back.
• Thought to be associated with HHV-6 or HHV-7 (human herpes viruses), though this is not fully confirmed.

"Multiple pink plaques with collarette scale"

• Collarette scale = The scaly ring has a unique inward-pointing scale pattern - like a ruffle pointing inward toward the center of the lesion.

---

SUNBURN

"Acute cutaneous inflammatory reaction due to excessive UV irradiation. Causes DNA mutations inducing apoptosis of keratinocytes. UVB is dominant in sunburn and photoAging. Exposure to UVA and UVB ↑ risk of skin cancer."

• UV irradiation = Ultraviolet radiation from the sun (or tanning beds).
• UVA vs UVB:
  • UVB = "B for Burn" - causes sunburn directly, mutates DNA, causes skin cancer. Blocked by regular glass. Peaks at midday.
  • UVA = "A for Aging" - penetrates deeper, causes photoaging (wrinkles, leathering), also contributes to cancer. Penetrates through glass.
• Apoptosis = Programmed cell death - when DNA damage is too severe, the cell kills itself to prevent becoming cancerous. The "sunburn cells" you see on biopsy are keratinocytes undergoing apoptosis.

---

RADIATION DERMATITIS

"Can be acute or late. Acute occurs ≤ 90 days after radiotherapy due to apoptosis of basal keratinocytes and epidermal edema. Presents with erythema, desquamation, superficial ulceration, and blistering."

• Radiotherapy = Radiation therapy for cancer - using X-rays to kill cancer cells.
• Basal keratinocytes = The stem cells at the base of the epidermis that keep replenishing the skin. Radiation kills these.
• Epidermal edema = Swelling of the outer skin layer.
• Desquamation = Peeling/shedding of damaged skin.

"Late occurs months to years after radiotherapy due to fibrosis with homogenization of dermal collagen fibers on histology, vascular damage, and telangiectasias."

• Fibrosis = Scarring - abnormal collagen deposition replaces normal tissue.
• Homogenization = The collagen fibers look uniform and glassy under microscope (loss of normal texture).
• Telangiectasias = Those little visible dilated blood vessels - permanent radiation damage to small vessels.

---

PAGE 493 - BURNS (Rule of Nines + Burn Classification)

---

RULE OF NINES

"Approximated by the rule of 9s. Used to assess the extent of burn injuries."

• Head = 9%
• Each arm = 9%
• Chest (front trunk) = 18% (9% chest + 9% abdomen)
• Back (posterior trunk) = 18%
• Each leg = 18% (9% thigh + 9% lower leg)
• Genitalia = 1%
• Total = 100%

---

INHALATION INJURY

"Inhalation injury - common complication of burns. Inhalation of noxious stimuli (eg, smoke) - heat, particulates (< 1 μm diameter), NH₃ (ammonia) → chemical tracheobronchitis, edema, pneumonia, acute respiratory distress syndrome (ARDS). Singed nasal hairs or soot in oropharynx continue on exam."

• Tracheobronchitis = Inflammation of the trachea (windpipe) and bronchi (airway branches).
• NH₃ = Ammonia - a toxic gas produced in many fires.
• ARDS (Acute Respiratory Distress Syndrome) = Severe lung failure where fluid fills the air sacs, making breathing impossible. High mortality.
• Singed nasal hairs = A clinical clue that the patient inhaled hot gases - if the hair inside the nose is burned, it suggests the airway is also burned.

---

BURN CLASSIFICATION TABLE

• Superficial = nerve endings intact = PAINFUL.
• Deep = nerve endings are destroyed = PAINLESS. Paradoxically, a painless burn is worse.

---

PAGE 494 - SKIN CANCER

---

BASAL CELL CARCINOMA (BCC)

"Most common skin cancer. Found in sun-exposed areas of body (eg, face). Locally invasive, but rarely metastasizes. Waxy, pink, pearly nodules, commonly with telangiectasias, rolled border, central crusting or ulceration."

• Basal cells = The bottom-most cells of the epidermis. They are the stem cells of the skin.
• Carcinoma = Cancer of epithelial cells.
• Locally invasive = It digs deep into surrounding tissues but almost NEVER spreads to other organs. This is why it is less deadly than melanoma.
• Pearly nodules = Shiny, almost translucent, round bumps - like a pearl. This is the classic description.
• Telangiectasias = Visible tiny blood vessels on/within the tumor - gives it a somewhat reddish appearance.
• Rolled border = The edge of the lesion rolls outward, giving it a raised, rim-like edge.
• Central ulceration = The center breaks down and creates an ulcer - "rodent ulcer" is the classic name because it looked like a rodent had gnawed through the skin.

"BCCs also appear as a scaling plaque (superficial BCC)"

• Not all BCCs are the pearly nodular type. Superficial BCC looks more like a scaly, flat red patch.

"Associated with immunosuppression, chronic nonhealing scars, chronic wounds, and occasionally arsenic exposure."

• Immunosuppression = In transplant patients on immunosuppressants or HIV patients, BCC risk is dramatically higher.
• Marjolin ulcer = A squamous cell carcinoma (not BCC, but important) arising in chronic nonhealing wounds/scars.

"BCC more common above upper lip. SCC more common below lower lip."

• A high-yield exam fact. BCC affects the nose, forehead, cheeks, upper lip. SCC affects the lower lip (from sun exposure and tobacco).

---

SQUAMOUS CELL CARCINOMA (SCC)

"Second most common skin cancer. Associated with immunosuppression, chronic nonhealing wounds, and occasionally arsenic exposure."

• SCC arises from squamous cells - the flat cells of the upper epidermis.
• Unlike BCC, SCC CAN metastasize - especially if it develops on mucous membranes, in chronic wounds, or in immunosuppressed patients.

"SCC arising in chronic wounds - Marjolin ulcer. Usually develops > 20 years after insult."

• A chronic wound (old burn scar, chronic venous ulcer) undergoes malignant transformation after decades. This is called a Marjolin ulcer.

"Locally invasive, may spread to lymph nodes."

• Unlike BCC which stays local, SCC can spread to regional lymph nodes and beyond.

"Actinic keratosis = premalignant lesion caused by sun exposure. Small, rough, erythematous brownish papules or plaques."

• Actinic = Related to sun/UV light ("actinic" = relating to radiation).
• Keratosis = Thickening of the keratin layer.
• These are the "pre-cancerous" lesions that can progress to SCC. Think of them as SCC-in-waiting. Found on sun-damaged skin.

---

MELANOMA

"Common tumor with significant risk of metastasis. S-100 tumor marker."

• Melanoma = Cancer of melanocytes (the pigment-producing cells in the skin).
• Although less common than BCC/SCC, melanoma is FAR more dangerous because it metastasizes early.
• S-100 = A protein marker found in melanocytes. Used on biopsy to confirm melanoma. Also found in neural tissue (melanocytes are neural crest-derived).

"Associated with dysplastic nevi; people with lighter skin tones are at ↑ risk."

• Dysplastic nevi = Atypical moles - larger, irregularly shaped moles that are precursors to melanoma.
• Lighter-skinned people have less melanin protection and are more susceptible to UV damage.

"Look for the ABCDEs: Asymmetry, Border irregularity, Color variation, Diameter > 6mm, Evolution over time."

• A - Asymmetry = One half doesn't match the other
• B - Border = Irregular, ragged, notched edges
• C - Color = Multiple shades (brown, black, red, white, blue)
• D - Diameter = > 6mm (size of a pencil eraser)
• E - Evolution = Changing over time (growing, changing color, bleeding)

"At least 4 different types of melanoma, including superficial spreading (most common), nodular, lentigo maligna, and acral lentiginous (highest prevalence in people with darker skin tones)"

• Superficial spreading = Most common; grows outward (horizontal) before going deep.
• Nodular = Most aggressive; grows straight down fast; dark, dome-shaped nodule.
• Lentigo maligna = Grows slowly on chronically sun-damaged skin in elderly; starts as a flat brown patch.
• Acral lentiginous = On palms, soles, under nails - this type is NOT caused by sun exposure, and is the most common type in darker-skinned people (like Bob Marley's toenail melanoma). This is important because it can be missed.

"Often driven by activating mutation in BRAF kinase. Primary treatment is excision with appropriately wide margins. Advanced melanoma also treat with immunotherapy (eg, ipilimumab) and/or BRAF inhibitors (eg, vemurafenib)."

• BRAF = A gene/protein in the MAPK signaling pathway that tells cells to grow. When mutated (BRAF V600E is the most common mutation), it gets stuck in the "ON" position and cells keep dividing = cancer.
• Vemurafenib = Specifically blocks the mutated BRAF kinase - targeted therapy.
• Ipilimumab = Blocks CTLA-4 on T-cells, releasing the "brakes" on the immune system so it can attack the tumor = checkpoint inhibitor immunotherapy.

---

PAGE 495 - ARACHIDONIC ACID PATHWAYS (Pharmacology)

---

THE BIG PICTURE

---

COX PATHWAY PRODUCTS:

• Key concept: PGI₂ and TXA₂ are OPPOSITES:
  • PGI₂ = keeps blood flowing, prevents clots (made by vessel walls)
  • TXA₂ = promotes clotting (made by platelets)
  • Aspirin blocks both by irreversibly inhibiting COX

"LTB₄ is a neutrophil chemotactic agent. PGI₂ is a vasodilator and platelet aggregation inhibitor."

• LTB₄ = Leukotriene B4 - recruits neutrophils (the white blood cells that fight infection) to the site of inflammation. This is why leukotrienes are important in conditions like asthma and allergic reactions.

---

LIPOXYGENASE PATHWAY PRODUCTS:

• LTC₄, LTD₄, LTE₄ = Bronchoconstrictors (narrow the airways) and increase mucus - these are the main culprits in ASTHMA.
• Montelukast, Zafirlukast = LEUKOTRIENE RECEPTOR ANTAGONISTS - they block these receptors and are used in asthma treatment.
• Zileuton = 5-Lipoxygenase inhibitor - blocks the enzyme that makes all leukotrienes.

---

PAGE 496 - NSAIDs AND RELATED DRUGS

---

ASPIRIN

Mechanism: "NSAID that irreversibly (aspirin) inhibits cyclooxygenase (both COX-1 and COX-2) by covalent acetylation → ↓ synthesis of TXA₂ and prostaglandins. Effect lasts until new platelets are produced."

• Irreversibly = Once aspirin binds, it STAYS bound permanently. The COX enzyme is inactivated forever.
• Covalent acetylation = Aspirin attaches an acetyl group to the serine residue of COX - a permanent chemical bond.
• TXA₂ = Thromboxane A2 - the clot-promoter. By blocking TXA2, aspirin prevents clotting → useful in heart attacks/strokes.
• "Effect lasts until new platelets are produced" = Platelets have no nucleus, so they CANNOT make new COX. The platelet is permanently disabled for its entire lifespan (~10 days). This is why aspirin has a lasting antiplatelet effect despite being taken once daily.

Clinical Use:

• Low dose (< 300 mg/day) = ↓ platelet aggregation → antiplatelet = prevent heart attacks/strokes
• Intermediate dose (300-2400 mg/day) = Antipyretic (lowers fever) and analgesic (relieves pain)
• High dose (2400-4000 mg/day) = Anti-inflammatory (for conditions like rheumatic fever)

Adverse Effects:

• Gastric ulceration = By blocking COX-1, aspirin removes prostaglandins that PROTECT the stomach lining. Without them, acid attacks the unprotected lining.
• Tinnitus = Ringing in the ears at high doses.
• CN VIII = Cranial nerve VIII (vestibulocochlear nerve) - aspirin at high doses damages hearing.
• Reye syndrome = Giving aspirin to children with viral infections (especially influenza or chickenpox) can cause a rare but deadly combination of liver failure + brain swelling. NEVER give aspirin to children with viral infections. Use acetaminophen instead.
• Respiratory alkalosis → metabolic acidosis = This is the classic aspirin overdose pattern:
  1. First: aspirin stimulates breathing → breathe out too much CO₂ → blood becomes alkaline (respiratory alkalosis)
  2. Then: aspirin uncouples oxidative phosphorylation → acid accumulates → metabolic acidosis

---

CELECOXIB

Mechanism: "Reversibly and selectively inhibits the cyclooxygenase (COX) isoform 2, found in inflammatory cells and vascular endothelium and mediates inflammation and pain; spares COX-1, which helps maintain gastric mucosa."

• COX-1 = The "housekeeping" COX - always present, makes prostaglandins that protect the stomach lining, maintain kidney function, and help platelets work.
• COX-2 = The "inducible" COX - activated during inflammation, makes prostaglandins that cause pain, swelling, fever.
• Celecoxib = Selectively blocks only COX-2, sparing COX-1 → LESS stomach side effects compared to non-selective NSAIDs.
• "Does not have the corrosive effects of other NSAIDs on the GI lining" = Because COX-1 is intact, the stomach stays protected.
• "Spares platelet function" = Platelets only have COX-1, not COX-2. So celecoxib doesn't interfere with platelet aggregation (unlike aspirin).

Clinical Use: Rheumatoid arthritis, osteoarthritis. Adverse Effects: ↑ risk of thrombosis (clotting), sulfa allergy (celecoxib has a sulfonamide side chain).

---

NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDs)

"Ibuprofen, naproxen, indomethacin, ketorolac, diclofenac, meloxicam, piroxicam."

• All reversibly inhibit COX-1 AND COX-2.
• Indomethacin = Special mention - used to CLOSE a Patent Ductus Arteriosus (PDA) in premature infants (the ductus arteriosus is kept open by prostaglandins; blocking prostaglandins closes it).
• Also used in gout attacks (very strong NSAID).

Adverse Effects:

• Interstitial nephritis = Inflammation of the kidney's filtering tissue.
• Gastric ulcers = From COX-1 inhibition (same as aspirin).
• Prostaglandins protect the afferent arteriole = The blood vessel entering the kidney. Block prostaglandins → constrict afferent arteriole → kidney gets less blood → renal ischemia (especially dangerous in patients already dependent on these prostaglandins to maintain kidney blood flow - like the elderly, heart failure patients).

---

LEFLUNOMIDE

Mechanism: "Reversibly inhibits dihydroorotate dehydrogenase, preventing pyrimidine synthesis. Suppresses T-cell proliferation."

• Pyrimidines = Building blocks of DNA and RNA (cytosine, thymine, uracil). Rapidly dividing cells (like activated T-cells in autoimmune disease) need lots of pyrimidines.
• By blocking their synthesis, T-cells cannot multiply → immune suppression → reduces joint inflammation in rheumatoid arthritis.

Clinical Use: Rheumatoid arthritis, psoriatic arthritis. Adverse Effects: Diarrhea, hypertension, hepatotoxicity (liver damage), teratogenicity (causes birth defects - NEVER use in pregnancy).

---

BISPHOSPHONATES

"Alendronate, ibandronate, risedronate, zoledronate."

Mechanism: "Pyrophosphate analogs; bind hydroxyapatite in bone, inhibiting osteoclast activity and promoting osteoclast apoptosis."

• Osteoclasts = The bone-breaking cells. They dissolve old bone to allow bone remodeling.
• Osteoblasts = The bone-making cells.
• In osteoporosis, osteoclasts are too active relative to osteoblasts → net bone loss.
• Bisphosphonates = Attach to hydroxyapatite crystals (the mineral component of bone). When osteoclasts try to dissolve bone, they swallow the bisphosphonate and die.
• Hydroxyapatite = The calcium-phosphate mineral that makes bones hard, like the "cement" of bone.

Clinical Use: Osteoporosis, hypercalcemia (high blood calcium), Paget disease of bone, metastatic bone disease, atypical femoral stress fractures, osteogenesis imperfecta (brittle bone disease).

Adverse Effects: Esophagitis (must take with lots of water and stay upright), osteonecrosis of the jaw (jaw bone death - especially in cancer patients receiving IV bisphosphonates), atypical femoral fractures (paradoxically, with long-term use, the bone becomes too "frozen" and develops stress fractures in unusual locations).

---

PAGE 497 - GOUT DRUGS

---

TERIPARATIDE, ABALOPARATIDE

"Recombinant PTH analog ↑ osteoblastic activity when administered in pulsatile fashion. Osteoporosis. Causes ↑ bone growth compared to antiresorptive therapies (eg, bisphosphonates). Dizziness, tachycardia, transient hypercalcemia, muscle spasms."

• PTH (Parathyroid hormone) = Normally, continuous PTH causes bone breakdown. But when given in PULSES (once daily injection), PTH paradoxically BUILDS bone by stimulating osteoblasts.
• Used when bisphosphonates fail or in severe osteoporosis.

---

PREVENTIVE GOUT DRUGS

"Competitive inhibitor of xanthine oxidase → ↓ conversion of hypoxanthine and xanthine to urate. Also used in lymphoma and leukemia to prevent tumor lysis-associated urate nephropathy. ↑ concentrations of xanthine oxidase active metabolites, azathioprine, and 6-MP."

• Gout = A condition where uric acid crystals deposit in joints (especially the big toe), causing severe pain.
• Xanthine oxidase = The enzyme that converts xanthine → uric acid (the final step in purine metabolism).
• Allopurinol = Blocks this enzyme → less uric acid made → lower blood uric acid → prevents gout attacks.
• Tumor lysis syndrome = When cancer cells are killed rapidly by chemotherapy, they release massive amounts of purines → uric acid floods the kidneys → acute kidney failure. Allopurinol prevents this.
• Azathioprine/6-MP warning = These cancer/immunosuppressant drugs are broken down BY xanthine oxidase. If you block xanthine oxidase with allopurinol, these drugs ACCUMULATE to toxic levels. This is a dangerous drug interaction.

"Recombinant uricase catalyzing uric acid to allantoin (a more water-soluble product). Inhibits xanthine oxidase. Think 'febu-xo-stat' makes 'xanthine oxidase static.'"

• Uricase = An enzyme that converts uric acid to allantoin (which is more soluble and easily excreted).
• Humans lack uricase naturally - that's why we get gout (other mammals don't).
• Rasburicase is the recombinant uricase drug.
• Febuxostat = Another xanthine oxidase inhibitor (alternative to allopurinol), especially used in patients with allopurinol hypersensitivity (particularly common in Asian patients with HLA-B*5801 allele).

"Inhibits reabsorption of uric acid in proximal convoluted tubule (also inhibits secretion of penicillin). Can precipitate uric acid calculi or lead to sulfa allergy."

• Probenecid = A uricosuric drug - it makes the kidney EXCRETE more uric acid.
• Normally, uric acid is filtered at the glomerulus and then reabsorbed in the proximal tubule. Probenecid blocks this reabsorption → more uric acid leaves in the urine.
• Penicillin = Probenecid also blocks penicillin secretion in the tubule, prolonging penicillin's effect. Historically used together to maintain higher penicillin levels.
• Risk: If you excrete lots of uric acid in the urine, it can crystallize in the urinary tract → kidney stones.

---

ACUTE GOUT DRUGS

"Binds and stabilizes tubulin to inhibit microtubule polymerization, impairing neutrophil chemotaxis and degranulation. Acute and prophylactic adverse effects. GI, cause myelosuppression, nephrotoxicity."

• Colchicine = From the crocus plant. It's been used for gout for centuries.
• Tubulin = The protein that makes up microtubules - the "scaffolding" inside cells.
• Microtubules = Tube-like structures inside cells used for cell division, cell movement, and transport. White blood cells use microtubules to move toward inflammation.
• Neutrophil chemotaxis = Neutrophils migrating toward the uric acid crystals. Colchicine prevents this migration → less inflammation.
• Degranulation = Neutrophils releasing their toxic contents onto the crystals. Colchicine prevents this too.
• Think of colchicine as "freezing" the neutrophils in place so they can't reach the joint.

---

PAGE 498 - TNF-α INHIBITORS, PSORIASIS BIOLOGICS, IMIQUIMOD

---

TNF-α INHIBITORS

"Fusion protein (decoy receptor for TNF-α + IgG1 Fc), produced by recombinant DNA."

• Decoy receptor = A fake receptor that floats in the blood and "traps" TNF-α before it can bind to real cell receptors. Think of it as a sponge that absorbs TNF-α.
• IgG1 Fc = The tail of an IgG antibody is attached to give the protein a longer half-life in the blood.
• Recombinant DNA = Manufactured in a lab using genetic engineering.

Clinical Use: Rheumatoid arthritis, psoriasis, ankylosing spondylitis.

"Etanercept intercepts TNF. Anti-TNF-α monoclonal antibody."

• Monoclonal antibody = A single identical antibody that directly binds and neutralizes TNF-α (vs. Etanercept which is a decoy receptor).
• "Etanercept intercepts" = Memory trick - Etanercept = intercepts TNF-α by acting as a decoy.

Adverse Effects: "Predisposition to infection, including reactivation of latent TB, since TNF is important in granuloma formation and stabilization. Can also lead to drug-induced lupus."

• Latent TB = Tuberculosis that's dormant in the body (held in check by granulomas formed by TNF-α). Blocking TNF-α destroys the granuloma's integrity → TB reactivates → active disease.
• Always screen for TB (with PPD or IGRA test) before starting TNF-α inhibitors.
• Drug-induced lupus = A lupus-like syndrome caused by the drug.

---

PSORIASIS BIOLOGICS (IL-12/17/23 Inhibitors)

• IL-12, IL-17, IL-23 = Interleukins (immune signaling molecules) that drive the inflammatory cascade in psoriasis.
• In psoriasis, the immune system (particularly Th17 cells driven by IL-23) produces IL-17, which causes keratinocytes to proliferate abnormally and produce inflammation.
• Blocking these interleukins = blocking the root cause of psoriasis.
• Clinical use includes: inflammatory bowel disease, rheumatoid arthritis, ankylosing spondylitis (for IL-12/23 blockers), and primarily psoriasis (for IL-17 and IL-23 blockers).

---

IMIQUIMOD

Mechanism: "Binds toll-like receptor 7 (TLR-7) of macrophages, monocytes, and dendritic cells to activate the topical antitumor immune response modifier."

• Toll-like receptors (TLRs) = Pattern recognition receptors on immune cells that detect "danger signals" - normally they detect viruses and bacteria. TLR-7 specifically recognizes single-stranded RNA (like from viruses).
• Imiquimod = A synthetic molecule that tricks TLR-7 into thinking there's a viral threat → activates the local immune response → the immune cells attack abnormal/infected cells.
• Think of it as "calling the immune police to the crime scene."

Clinical Use: Anogenital warts (HPV infection), actinic keratosis.

Adverse Effects: Itching, burning pain at site of application, rashes (because it IS activating inflammation locally - that's how it works).

---

SUMMARY - THE KEY TAKE-HOME POINTS

---