---

How I Can Help You - Vet Student (Clinical Cases)

• You present the signalment, history, and clinical signs
• I help you build a problem list, generate a differential diagnosis list, and prioritize differentials
• We discuss which diagnostics to run and why

• Walk through CBC, biochemistry panels, urinalysis, imaging findings, cytology, histopathology
• Explain what abnormalities mean and how they narrow your differentials

• Discuss treatment options with mechanisms of action
• Drug dosages, protocols, and monitoring parameters
• Supportive care rationale

• If a case involves a disease you don't fully understand, I can explain the underlying pathophysiology in detail

• After working through a case, I can summarize key learning points and give you similar cases to test yourself

---

• Species, breed, age, sex
• Chief complaint / history
• Clinical findings
• Any diagnostics already done

---

Building a Differential Diagnosis List

Step 1 - Extract the Key Problems

• Problem 1: PU/PD
• Problem 2: Pot-bellied abdomen
• Problem 3: Recurrent pyoderma

---

Step 2 - Use a Systematic Framework (DAMNIT-V)

---

Step 3 - Apply Patient Filters (Narrow the List)

• Species - Cats don't get Addison's commonly; dogs do. Hyperthyroidism is common in cats, rare in dogs.
• Breed - Boxers are prone to mast cell tumors. Dobermans to dilated cardiomyopathy. Bernese Mountain Dogs to histiocytic sarcoma.
• Age - Young animals: congenital, infectious, nutritional. Middle-aged: metabolic, immune-mediated. Old: neoplastic, degenerative.
• Sex / reproductive status - Intact female dog with PU/PD and vaginal discharge? Pyometra moves to the top immediately.
• Vaccination / travel history - Unvaccinated puppy with hemorrhagic diarrhea? Parvovirus is #1.
• Onset and progression - Acute vs. chronic, progressive vs. static, episodic vs. continuous.

---

Step 4 - Rank Your Differentials

1. Probability - What is most likely given this patient's signalment, history, and clinical findings?
2. Consequence - What can you NOT afford to miss, even if less likely? (e.g., a toxic ingestion, a ruptured GDV, a pneumothorax)

• Rule-outs (R/O): Must be excluded because they are life-threatening or very likely
• Likely: Fits the overall picture well
• Less likely but possible: Don't discard; revisit if top differentials are excluded

---

Step 5 - Design Diagnostics to Discriminate

"Which differential does this test help me confirm or rule out?"

• CBC + biochemistry panel - screens broadly for metabolic, inflammatory, and organ disease
• Urinalysis + urine culture - essential for PU/PD cases
• Imaging (radiographs, ultrasound) - organ size, masses, effusions, structural abnormalities
• Specific tests (ACTH stim, TLI, bile acids, FELV/FIV, PCR panels) - targeted once your top differentials are known

---

Step 6 - Revisit and Revise

• Cross off differentials that are excluded
• Promote differentials that gain supporting evidence
• Add new differentials if unexpected findings emerge

---

Quick Summary Framework

1. Build problem list from history + PE
2. Pick key problem(s)
3. Apply DAMNIT-V to generate broad DDx
4. Filter by signalment (species, breed, age, sex, history)
5. Rank by probability + consequence
6. Choose targeted diagnostics
7. Revise as results come in

---

---

10 Important Diseases of Dogs and Cats

---

DOGS

---

1. Canine Parvovirus (CPV-2)

• Profuse, hemorrhagic, foul-smelling diarrhea
• Severe vomiting
• Depression, anorexia
• Fever (or hypothermia in severe cases)
• Dehydration

• SNAP ELISA fecal antigen test (in-clinic)
• CBC: leukopenia (neutropenia + lymphopenia) is characteristic
• PCR for confirmation

---

2. Canine Distemper

• Respiratory: Nasal/ocular discharge, pneumonia
• GI: Vomiting, diarrhea
• Neurological: Seizures, myoclonus (rhythmic muscle twitching - characteristic), ataxia, paresis
• Skin: Hyperkeratosis of nose and footpads ("hard pad disease")
• Teeth: Enamel hypoplasia in surviving puppies

---

3. Hyperadrenocorticism (Cushing's Disease)

• Polyuria / Polydipsia
• Polyphagia
• Pot-bellied abdomen (muscle wasting + hepatomegaly + fat redistribution)
• Bilateral symmetrical alopecia
• Skin thinning, calcinosis cutis
• Recurrent infections (immunosuppression)
• Muscle weakness

• Screening: UCCR (urine cortisol:creatinine ratio), LDDS test (low-dose dexamethasone suppression)
• Differentiating PDH vs. ADH: HDDS test (high-dose), abdominal ultrasound, endogenous ACTH
• CBC: "stress leukogram" (neutrophilia, eosinopenia, lymphopenia), elevated ALP

• PDH: Trilostane or mitotane (o,p'-DDD)
• ADH: Adrenalectomy preferred

---

4. Canine Hip Dysplasia

• Hindlimb lameness (often bilateral)
• "Bunny hopping" gait
• Reluctance to rise, exercise intolerance
• Pain on hip extension
• Crepitus on joint manipulation
• Muscle atrophy of hindquarters

• Conservative: weight management, physiotherapy, NSAIDs (meloxicam, carprofen), joint supplements
• Surgical: triple pelvic osteotomy (young dogs), femoral head and neck excision (FHO), total hip replacement (THR)

---

5. Canine Gastric Dilatation-Volvulus (GDV)

• Non-productive retching (hallmark sign)
• Distended, tympanic abdomen
• Hypersalivation, restlessness
• Rapid progression to collapse, shock (pale mucous membranes, weak pulse, tachycardia)

1. IV access (2 large-bore catheters), aggressive fluid resuscitation
2. Gastric decompression (orogastric tube or trocarization)
3. Emergency surgery: derotation, gastropexy, resection of necrotic stomach/spleen

• Prophylactic gastropexy offered to at-risk breeds

---

6. Canine Babesiosis

• Pale or icteric mucous membranes
• Hemoglobinuria ("port-wine" colored urine)
• Fever, weakness, collapse
• Splenomegaly

---

CATS

---

7. Feline Hyperthyroidism

• Weight loss despite polyphagia (classic combination)
• Hyperactivity, restlessness, aggression
• Vomiting, diarrhea
• Unkempt coat
• Tachycardia, heart murmur, gallop rhythm
• Hypertension (secondary)
• Goiter (palpable thyroid nodule in ~90%)

• Methimazole (daily medication - medical management)
• Radioactive iodine (I-131) - curative, treatment of choice
• Surgical thyroidectomy - curative
• Dietary iodine restriction (Hill's y/d)

---

8. Feline Lower Urinary Tract Disease (FLUTD) / Feline Idiopathic Cystitis (FIC)

• Dysuria, stranguria, pollakiuria
• Hematuria
• Periuria (urinating outside litter box)
• In urethral obstruction: straining with no urine production, vocalization, collapse, bradycardia (life-threatening hyperkalemia)

• FIC: stress reduction (environmental enrichment), increased water intake, urinary diets, pain management
• Urethral obstruction: EMERGENCY - urethral catheterization, IV fluids, treat hyperkalemia (ECG monitoring)
• Urolithiasis: dietary dissolution (struvite) or surgical removal (oxalate)

---

9. Feline Infectious Peritonitis (FIP)

• Wet (effusive): Immune complex deposition in vessels leads to protein-rich effusions in body cavities
• Dry (non-effusive): Granuloma formation in organs (CNS, eyes, liver, kidneys)

• Wet: Distended abdomen (ascites) or pleural effusion, dyspnea, fever, weight loss
• Dry: Neurological signs (ataxia, seizures), uveitis, chorioretinitis, organomegaly

---

10. Feline Chronic Kidney Disease (CKD)

• PU/PD
• Weight loss, muscle wasting
• Vomiting, anorexia
• Halitosis (uremic breath)
• Pale mucous membranes (non-regenerative anemia)
• Hypertension (retinal detachment, sudden blindness)
• Dehydration, poor coat

• Renal diet (phosphorus restriction, moderate protein)
• Phosphate binders (aluminum hydroxide, lanthanum carbonate)
• Antihypertensives (amlodipine)
• Erythropoiesis-stimulating agents for anemia (darbepoetin)
• Sub-cutaneous fluids (home management)
• Treat concurrent conditions (UTI, hypertension, proteinuria)

---

11. Feline Asthma (Chronic Bronchial Disease)

• Episodic coughing (crouching, neck extended - classic posture)
• Wheezing
• Increased respiratory effort (abdominal breathing)
• Acute respiratory distress during attacks

• Acute attack: Oxygen, bronchodilators (terbutaline SC, albuterol inhaler)
• Long-term: Inhaled corticosteroids (fluticasone via AeroKat spacer), inhaled bronchodilators (albuterol as needed)
• Identify and eliminate allergen triggers

---

12. Canine/Feline Diabetes Mellitus

• PU/PD, polyphagia
• Weight loss
• Cataracts (dogs - rapidly progressive)
• Plantigrade stance (cats - diabetic neuropathy)
• Recurrent infections

---

Quick Reference Summary Table

---

---

10 Skin Diseases of Dogs and Cats

---

1. Canine Atopic Dermatitis (CAD)

• Pruritus (the primary sign) - often seasonal at first, becomes year-round
• Erythema and self-trauma lesions at characteristic sites: face (periocular, perioral), ears (otitis externa), ventral abdomen, axillae, groin, interdigital spaces
• Alopecia, lichenification, and hyperpigmentation with chronicity
• Recurrent pyoderma and Malassezia otitis/dermatitis

• Diagnosis of exclusion - must rule out flea allergy and food allergy first (Favrot criteria used clinically)
• Intradermal allergy testing (IDAT) or serum allergen-specific IgE testing for identifying triggers
• Skin cytology to identify secondary infections

• Acute flares: corticosteroids (prednisolone), oclacitinib (Apoquel - JAK1 inhibitor), lokivetmab (Cytopoint - anti-IL-31 monoclonal antibody)
• Long-term: allergen-specific immunotherapy (ASIT) - the only disease-modifying option
• Skin barrier support: essential fatty acid supplementation, medicated shampoos
• Treat secondary infections concurrently

---

2. Flea Allergy Dermatitis (FAD)

• Dogs: Intense pruritus over the dorsal lumbosacral area ("flea triangle"), tail base, caudal thighs, and flanks. Secondary lesions: papules, crusts, alopecia, hot spots (acute moist dermatitis)
• Cats: Miliary dermatitis (tiny crusted papules all over the body, especially dorsal), symmetric self-induced alopecia (ventral abdomen, inner thighs), eosinophilic granuloma complex lesions

• Clinical distribution + response to flea control
• Finding fleas or flea dirt (comma-shaped reddish-brown specks) - note: may be absent in highly grooming cats
• Intradermal test with flea antigen

• Strict flea control on ALL pets in the household AND environment (premise sprays with IGR)
• Fast-acting adulticides: afoxolaner (NexGard), fluralaner (Bravecto), sarolaner (Simparica)
• Anti-pruritic therapy during acute phase (prednisolone, oclacitinib)

---

3. Canine Pyoderma (Bacterial Skin Infection)

• Surface pyoderma: Skin fold dermatitis, hot spots (acute moist dermatitis), mucocutaneous pyoderma
• Superficial pyoderma: Impetigo (puppies), superficial bacterial folliculitis (most common)
• Deep pyoderma: Furunculosis, cellulitis, fistulous tracts

• Superficial: papules, pustules, epidermal collarettes (pathognomonic - circular crusted lesion with peeling edge), alopecia, "moth-eaten" coat
• Deep: nodules, draining tracts, crusted plaques, pain, fever

• Skin cytology: intracellular cocci within neutrophils (confirms infection vs. colonization)
• Culture and sensitivity (C&S): essential for recurrent/deep cases and suspected MRSP (methicillin-resistant S. pseudintermedius)

• Superficial: topical antibiotics/antiseptics (chlorhexidine shampoos, sprays) ± oral antibiotics (amoxicillin-clavulanate, cefalexin) for 3-4 weeks
• Deep: 6-8+ weeks antibiotics guided by C&S
• Always investigate and treat the underlying cause

---

4. Malassezia Dermatitis

• Intense pruritus, greasy/oily skin
• Characteristic "rancid" or "corn chip" odor
• Erythema, hyperpigmentation, lichenification (elephant skin appearance in chronic cases)
• Distribution: skin folds, ventral neck, axillae, groin, interdigital spaces, ears (otitis)
• Yellow-brown waxy debris in ear canals

• Skin cytology (tape strip or cotton swab - Diff-Quik stain): peanut-shaped or "footprint"-shaped yeast organisms (>2/high-power field is significant)

• Topical: miconazole/chlorhexidine shampoos (leave-in contact 10 minutes), leave-on mousses
• Systemic: ketoconazole or itraconazole for 3-4 weeks in widespread/refractory cases
• Treat underlying disease (usually atopy)

---

5. Dermatophytosis (Ringworm)

• Classic: circular patches of alopecia with scale and crusting (hence "ringworm" - no actual worm)
• Cats: often asymptomatic carriers (especially longhaired cats) or show patchy alopecia on face, ears, and forelimbs. Kerion (inflammatory nodule) in some cases
• Dogs: more obviously inflamed lesions; generalized form possible in immunocompromised animals

• Wood's lamp: M. canis fluoresces apple-green (only ~50% of strains fluoresce - negative result does not rule out)
• Direct microscopy (KOH prep or fungal stain): hyphae and arthrospores around hair shafts
• Fungal culture on DTM (Dermatophyte Test Medium): red color change + colony growth (gold standard, takes 1-3 weeks)
• PCR: fastest and most sensitive

• Topical: miconazole/chlorhexidine shampoo (twice weekly) or lime sulfur dips
• Systemic: itraconazole (drug of choice for cats), terbinafine, or griseofulvin
• Environmental decontamination: vacuum, disinfect with dilute bleach (1:10), wash bedding
• Treat until two consecutive negative cultures

---

6. Canine Demodicosis (Demodex)

• Localized: <5 patches, young dogs, 90% self-resolving
• Generalized: >5 patches OR affects entire body/body region; requires treatment

• NON-PRURITIC (or mildly pruritic) alopecia - key differentiating feature from allergic diseases
• Erythema, scaling, comedones, follicular casts
• Deep demodicosis: furunculosis, draining tracts, secondary bacterial infection (very pruritic at this stage), systemic illness

• Deep skin scraping: multiple sites, scrape until capillary bleeding, look for mites under microscopy. Finding ANY mites is significant (except on face/feet where low numbers are normal)
• Hair pluck/trichogram: useful for paws and face
• Skin biopsy for refractory cases

• Localized: often monitor; topical amitraz if treatment desired
• Generalized: isoxazoline class (afoxolaner, fluralaner, sarolaner) - now first-line, highly effective. Amitraz dips (second-line). Treat until 2 negative scrapings one month apart.
• Always treat secondary pyoderma and investigate underlying cause in adult-onset cases

---

7. Sarcoptic Mange (Scabies)

• INTENSELY PRURITIC - often described as the "most pruritic disease" in dogs
• Starts at sparsely haired areas: ear margins, elbows, hocks, and ventral abdomen
• Erythematous papules, thick yellow/grey crusts
• Alopecia, excoriations, secondary pyoderma with chronicity
• Pinnal-pedal reflex: scratching response when ear margin is rubbed - 75-90% sensitive for sarcoptes

• Skin scrapings: mites found in only ~50% of cases (superficial scraping of multiple sites)
• Serology (ELISA): useful when scrapings negative
• Diagnosis often made clinically + response to treatment (therapeutic trial)

• Isoxazolines (afoxolaner, fluralaner, sarolaner) - highly effective, now preferred
• Selamectin (Revolution) - 2 doses 4 weeks apart
• Amitraz dips (older protocol)
• Treat ALL in-contact dogs. Environmental treatment generally unnecessary (mite survives only days off host)

---

8. Feline Eosinophilic Granuloma Complex (EGC)

• Clinical appearance is often diagnostic
• Cytology (fine needle aspirate): eosinophils, mast cells, occasionally collagen degeneration
• Biopsy for confirmation and to rule out neoplasia
• Identify and test for underlying allergy

• Treat the underlying trigger (flea control, diet trial, environmental allergy management)
• Immunosuppressive doses of prednisolone for acute lesions
• Refractory cases: ciclosporin, chlorambucil, megestrol acetate (last resort)

---

9. Canine Sebaceous Adenitis (SA)

• Two forms based on coat type:
  • Long-coated breeds (Poodle): Tightly adhered silver-white scales along hair shafts (follicular casting), dull/brittle coat, progressive alopecia, musty odor
  • Short-coated breeds (Akita, Vizsla): Circular, moth-eaten alopecia with fine scaling, less follicular casting

• Skin biopsy: absence or destruction of sebaceous glands (nodular granulomatous inflammation around glands in early disease; complete absence in end-stage)

• Emollient therapy: essential fatty acid supplementation, oil sprays/soaks before bathing (baby oil or coconut oil), antiseborrheic shampoos
• Immunosuppression: ciclosporin (most effective systemic treatment)
• Retinoids (isotretinoin, acitretin) in some cases

---

10. Canine/Feline Pemphigus Foliaceus (PF)

• Primary lesions: large, fragile superficial pustules (often already ruptured by the time of examination)
• Secondary lesions: crusts and erosions - often thick, yellow-honey colored crusts
• Characteristic distribution: face (nasal planum, periocular), pinnae, and footpads (footpad hyperkeratosis and crusting is a hallmark, especially in cats)
• May be pruritic or non-pruritic
• Nasal planum involvement commonly causes loss of normal cobblestone architecture

• Cytology of intact pustule or underside of crust: acantholytic keratinocytes (large, round keratinocytes with central nuclei surrounded by neutrophils) - highly suggestive
• Skin biopsy: subcorneal pustule with acantholytic keratinocytes (confirmatory)
• Immunofluorescence or immunohistochemistry to demonstrate autoantibody deposition

• Immunosuppressive doses of prednisolone (2-4 mg/kg/day) initially
• Steroid-sparing agents added for long-term control: azathioprine (dogs), chlorambucil (cats - azathioprine is toxic to cats), ciclosporin, mycophenolate mofetil
• Lifelong treatment usually required; aim for lowest effective immunosuppressive dose

---

Quick Reference Summary Table

---

1. Is this allergic? (atopy, FAD, food allergy) - pruritus is the driver
2. Is this infectious? (bacteria, yeast, fungus, parasites) - often secondary to allergic disease
3. Is this immune-mediated or neoplastic? - consider if distribution is atypical or lesions don't respond to standard treatment

---

The 10 Skin Diseases Already Explained

---

• Pathophysiology
• Signalment (who gets it)
• Clinical signs
• Diagnosis
• Treatment

---

• A different set of 10 skin diseases
• Diseases explained in a different format (e.g., shorter notes, table only, or focused on one species)
• A specific category of skin disease (e.g., only parasitic, only fungal, only autoimmune)

10 Skin Diseases of Dogs & Cats — Tabular Format with Differential Focus

---

MASTER COMPARISON TABLE — All 10 Diseases at a Glance

---

DIFFERENTIAL DIAGNOSIS FOCUS — By Presenting Complaint

---

🔴 COMPLAINT 1: Intense Pruritus

---

🟠 COMPLAINT 2: Alopecia (Hair Loss)

---

🟡 COMPLAINT 3: Pustules and Crusts

---

🟢 COMPLAINT 4: Facial + Nasal Planum Lesions (Crucial for Differentials)

---

🔵 COMPLAINT 5: Cat-Specific Skin Presentations

---

DIFFERENTIAL DIAGNOSIS DECISION TREE

PRURITIC SKIN DISEASE?
│
├── YES ──► Is distribution LUMBOSACRAL / TAIL BASE?
│           ├── YES + flea dirt ──► FLEA ALLERGY DERMATITIS
│           └── NO ──► Is distribution FEET/FACE/EARS/GROIN?
│                       ├── YES ──► ATOPIC DERMATITIS (rule out FAD + food allergy first)
│                       └── EAR MARGINS + ELBOWS + HOCKS?
│                           └── YES + pinnal-pedal reflex ──► SARCOPTIC MANGE
│
└── NON-PRURITIC (or mild) ALOPECIA?
    ├── Deep skin scraping POSITIVE ──► DEMODICOSIS
    ├── DTM culture POSITIVE ──► DERMATOPHYTOSIS
    ├── Silver follicular casts + Poodle/Akita ──► SEBACEOUS ADENITIS
    └── Systemic signs (obesity, bradycardia) ──► HYPOTHYROIDISM / HYPERADRENOCORTICISM

PUSTULES + CRUSTS?
├── Cytology: intracellular cocci ──► PYODERMA
├── Cytology: acantholytic cells ──► PEMPHIGUS FOLIACEUS
├── Footpad + nasal planum + pinnae ──► PEMPHIGUS FOLIACEUS (first choice)
└── Culture: dermatophyte ──► DERMATOPHYTOSIS

CAT with EOSINOPHILIC LESION?
├── Upper lip ulcer ──► INDOLENT ULCER (EGC)
├── Moist raised plaque on abdomen ──► EOSINOPHILIC PLAQUE (EGC)
└── Linear thigh lesion / oral nodule ──► EOSINOPHILIC GRANULOMA (EGC)
    └── In all 3 ──► FIND THE TRIGGER (FAD > food allergy > atopy)

---

KEY EXAM MNEMONICS

• Sarcoptic mange
• Atopic dermatitis
• Demodicosis
• Malassezia dermatitis
• Autoimmmune (Pemphigus Foliaceus)
• Pyoderma
• Flea Allergy Dermatitis
• Dermatophytosis
• Pemphigus... (EGC for cats)
• Sebaceous adenitis

---

Sarcoptes > FAD = Atopy > Malassezia > Pyoderma > Pemphigus > EGC > Dermatophytosis = Demodicosis > Sebaceous Adenitis

---

CRITICAL EXAM TRAPS & MISCONCEPTIONS

---

TOP VIVA QUESTIONS

1. How do you differentiate superficial pyoderma from pemphigus foliaceus on cytology?
2. What is the pinnal-pedal reflex and which disease is it associated with?
3. Why must you investigate for underlying disease in adult-onset demodicosis?
4. Name the three forms of eosinophilic granuloma complex in cats and their locations.
5. Why can treating feline hyperthyroidism unmask renal disease? (bonus systemic question)
6. What is the gold standard for diagnosing sebaceous adenitis?
7. Which immunosuppressive drug is contraindicated in cats and why?
8. Name two zoonotic skin diseases of dogs and their causative agents.
9. What does a positive Rivalta's test indicate in a cat with ascites? (links to FIP)
10. What is the mechanism of action of oclacitinib (Apoquel)?

---

10 Skin Diseases — Clinical Signs & Differentials (Deep Focus)

---

PART 1: CLINICAL SIGNS IN DETAIL — Disease by Disease

---

DISEASE 1: Atopic Dermatitis (AD)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

FACE:     Periocular (raccoon eyes), perioral, chin
EARS:     Pinnae, ear canal (otitis externa)
FEET:     Interdigital spaces, paw pads, dorsum of paws
BODY:     Axillae, groin, ventral abdomen, perineum

Early: Seasonal pruritus, mild erythema, face/feet
↓
Intermediate: Year-round, otitis, pododermatitis, secondary infections
↓
Chronic: Lichenification, hyperpigmentation, permanent skin changes

---

DISEASE 2: Flea Allergy Dermatitis (FAD)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

Finding flea dirt (reddish-brown comma-shaped specks that turn red on wet cotton) confirms flea exposure. BUT in cats that over-groom, fleas may be completely absent despite active infestation.

---

DISEASE 3: Superficial Pyoderma (Bacterial Skin Infection)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

---

DISEASE 4: Malassezia Dermatitis

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

Ventral neck → Axillae → Groin → Perineum
Ear canals (brown waxy debris)
Interdigital spaces
Lip folds, facial folds
Ventral tail

Acute: Erythema + mild scale + mild pruritus
↓
Subacute: Greasy scale + moderate pruritus + early lichenification
↓
Chronic: Severe lichenification + hyperpigmentation + alopecia (elephant skin)

---

DISEASE 5: Dermatophytosis (Ringworm)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

---

DISEASE 6: Demodicosis

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

If demodicosis is generalized AND the dog is >4 years old at first presentation → ALWAYS investigate for underlying immunosuppressive disease (hyperadrenocorticism, hypothyroidism, neoplasia, long-term steroid use, diabetes mellitus)

---

DISEASE 7: Sarcoptic Mange

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

WEEK 1-2:   Intense pruritus, erythematous papules on ear margins and elbows
↓
WEEK 3-4:   Crusting of ear margins (pathognomonic), excoriations, alopecia
↓
WEEK 5-8:   Spreads to hocks, ventral chest, lateral elbows, face
↓
CHRONIC:    Thick grey/yellow crusts, widespread alopecia, lichenification,
            lymphadenopathy, emaciation in neglected cases

---

DISEASE 8: Pemphigus Foliaceus (PF)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

Nasal planum ──────► Loss of normal cobblestone texture (PATHOGNOMONIC)
Pinnae (ear flap) ──► Thick crusting on inner pinna surface
Periocular ─────────► Crusted patches around eyes
Footpads ───────────► Hyperkeratosis + crusting (especially in CATS)

---

DISEASE 9: Feline Eosinophilic Granuloma Complex (EGC)

Clinical Signs — Easy Language First

Clinical Signs — Three Forms in Detail:

---

DISEASE 10: Sebaceous Adenitis (SA)

Clinical Signs — Easy Language First

Clinical Signs — Scientific Detail

---

PART 2: MASTER DIFFERENTIAL DIAGNOSIS TABLES

---

TABLE A: Differentiating by PRURITUS LEVEL

---

TABLE B: Differentiating by LESION TYPE

---

TABLE C: Differentiating by DISTRIBUTION

---

TABLE D: THE MOST CRITICAL DIFFERENTIALS — Pyoderma vs PF vs Demodicosis

---

TABLE E: CYTOLOGY — The Most Powerful In-Clinic Differentiator

---

TABLE F: ZOONOTIC RISK SUMMARY

---

CLINICAL CASE SCENARIOS FOR EXAM PRACTICE

---

A 2-year-old male Golden Retriever presents with redness and hair loss between all four paws, red ears with dark waxy discharge, and a rancid odor. The pruritus is scored 8/10. He was diagnosed with "ear infection" twice in the past year. His littermate has similar signs.

• Primary: Atopic Dermatitis with secondary Malassezia otitis/pododermatitis
• DDx: Food allergy (identical presentation), FAD (check for flea dirt)
• Next step: Rule out FAD (flea control trial 3 months) → Rule out food allergy (diet trial 8-12 weeks) → If eliminated, diagnose atopy and pursue allergy testing

---

A 7-year-old intact female Akita presents with circular patches of hair loss on the dorsal neck and top of head. White scales are tightly stuck to the hair shafts. The dog is not pruritic. The owner says the coat has been getting dull for the past 2 years.

• Primary: Sebaceous adenitis
• DDx: Hypothyroidism (check T4), demodicosis (skin scraping), dermatophytosis (DTM culture)
• Gold standard: Skin biopsy showing absent/destroyed sebaceous glands

---

A 5-year-old DSH cat presents with a painless, shiny ulcer on the upper right lip that has been present for 3 months. The cat eats normally and is not distressed. You find no fleas. The owner has two other cats with no skin problems.

• Primary: Indolent ulcer (EGC)
• DDx: Squamous cell carcinoma (older cats, sun-exposed), trauma, eosinophilic plaque (but that is pruritic and on abdomen)
• Next step: Cytology/biopsy → identify underlying trigger (start with strict flea control even if no fleas seen, then food trial)

---

1. What is the "pinnal-pedal reflex" and what does a positive result suggest?
2. Name three skin diseases where footpad lesions are a prominent feature.
3. What is the difference in pruritus level between demodicosis and sarcoptic mange and why?
4. A cat presents with symmetric hair loss on the ventral abdomen. Name 4 differentials.
5. What does an epidermal collarette represent histologically?
6. How do you distinguish between indolent ulcer and squamous cell carcinoma in a cat?
7. Why does Malassezia dermatitis cause disproportionate pruritus relative to the organism numbers?
8. Name the three forms of EGC and their classic locations.
9. What clinical sign in pemphigus foliaceus differentiates it from discoid lupus erythematosus?
10. A dog presents with non-pruritic alopecia periocularly. What is your #1 differential and what test confirms it?

---