Learning Objectives
Differentiate between common inflammatory and proliferative skin disorders. Master the specific histological markers for Psoriasis (Auspitz sign, Munro microabscesses), the hypersensitivity profiles of Atopic vs. Contact Dermatitis, and the “stuck-on” morphology of Seborrheic Keratosis.
1. Inflammatory & Follicular Disorders
These conditions are driven by hormonal, environmental, or mechanical triggers affecting the pilosebaceous unit or general skin barrier.
| Condition | Pathophysiology / Clinical Findings | High-Yield Notes |
|---|---|---|
| Acne Vulgaris | ↑ Sebum/androgens, Cutibacterium acnes colonization, and inflammation. | Treat with retinoids, benzoyl peroxide, and antibiotics. |
| Rosacea | Inflammatory facial erythema, papules, and pustules; no comedones. | Associated with alcohol/heat flushing; risk of rhinophyma. |
| Pseudofolliculitis Barbae | Inflammatory reaction to hair penetrating the skin (“razor bumps”). | Common in curly hair; it occurs near the jawline from shaving. |
| Keratosis Pilaris | Follicular-based papules from keratin plugging. | Common on extensor surfaces (arms/thighs). |
2. Dermatitis & Hypersensitivity
It is vital to distinguish between systemic “atopy” and localized “contact” reactions based on morphology and distribution.
| Condition | Type of Reaction | Clinical Distribution |
|---|---|---|
| Atopic Dermatitis (Eczema) | Pruritic; associated with ↑ IgE and asthma/allergic rhinitis. | Infants: Face. Adults: Flexural surfaces. |
| Allergic Contact Dermatitis | Type IV Hypersensitivity secondary to nickel, poison ivy, or drugs. | Localized to the site of contact. |
| Urticaria (Hives) | Mast cell degranulation leading to wheals. | Superficial dermal edema and lymphatic dilation. |
3. Papulosquamous & Proliferative Disorders
These conditions involve changes in the rate of epidermal growth or abnormal maturation of keratinocytes.
| Condition | Histology / Findings | High-Yield Diagnosis |
|---|---|---|
| Psoriasis | Acanthosis, Parakeratosis, Munro microabscesses. | Auspitz sign (bleeding scale); Silvery scaling on knees/elbows. |
| Seborrheic Keratosis | Verrucous proliferation with keratin-filled “horn cysts”. | Leser-Trélat sign: Rapid onset indicates GI adenocarcinoma. |
| Verrucae (Warts) | Epidermal hyperplasia and koilocytosis (HPV). | Cauliflower-like papules; low-risk HPV strains. |
| Melanocytic Nevus | Common mole. | Junctional (flat) vs. Intradermal (papular). |
Activity: Clinical Vignette Challenge
High-Yield Mnemonics & Signs:
- Psoriasis Path: ↑ Spinosum, ↓ Granulosum (The grain is lost, but the spine is thick).
- Auspitz Sign: Think “Aww pits”—pinpoint bleeding when the scale is pulled.
- Stuck-on: Seborrheic keratosis looks like a “burnt coin” stuck onto the skin.
- Atopic Flexion: Atopic occurs in Flexures (kneecaps/elbow pits). Psoriasis occurs on Extensors.