A 38-year-old woman presents with a 6-month history of progressive skin lesions on her face, neck, and upper trunk. She reports itching and occasional bleeding from the lesions. On examination, she has multiple erythematous, scaly plaques with well-demarcated borders and a silvery scale. Some lesions show pinpoint bleeding when the scale is gently scraped. She denies systemic symptoms. Her family history is significant for similar skin disease in her mother. What is the most likely diagnosis?

Explanation

## Diagnosis: Psoriasis ### Clinical Features Matching the Case **Key Point:** The combination of erythematous scaly plaques with well-demarcated borders, silvery scale, and pinpoint bleeding (Auspitz sign) on gentle scraping is pathognomonic for psoriasis. ### Pathological Features | Feature | Psoriasis | Lichen Planus | Seborrheic Keratosis | |---------|-----------|---------------|----------------------| | **Appearance** | Erythematous plaques, silvery scale | Violaceous papules, flat-topped | Waxy, brown, verrucous | | **Auspitz sign** | Positive (pinpoint bleeding) | Negative | Negative | | **Wickham striae** | Absent | Present on oral lesions | Absent | | **Distribution** | Extensor surfaces, scalp, nails | Wrists, ankles, oral mucosa | Face, trunk, elderly | | **Family history** | Common (30–50%) | Uncommon | Uncommon | | **Histology** | Parakeratosis, acanthosis, dilated capillaries | Saw-tooth acanthosis, band-like lymphocytic infiltrate | Benign acanthosis, horn cysts | ### Histopathology of Psoriasis 1. **Parakeratosis** — retention of nuclei in the stratum corneum (hallmark) 2. **Acanthosis** — epidermal hyperplasia with elongated rete ridges 3. **Dilated and tortuous capillaries** in the dermal papillae → Auspitz sign (pinpoint bleeding) 4. **Reduced/absent granular layer** 5. **Neutrophilic microabscesses** in the stratum corneum (Munro microabscesses) ### Clinical Pearl **High-Yield:** The **Auspitz sign** (pinpoint bleeding on gentle scraping) and **Koebner phenomenon** (lesions appearing at sites of trauma) are characteristic of psoriasis. The patient's positive family history supports a genetic predisposition (HLA-Cw6 association). ### Why Psoriasis Over Other Differentials - **Lichen planus** presents with violaceous, flat-topped papules (not scaly plaques) and Wickham striae on oral lesions; no pinpoint bleeding. - **Seborrheic keratosis** is a benign proliferation with a waxy, stuck-on appearance; typically seen in older patients and lacks the inflammatory features. - **Pityriasis rosea** is acute, self-limited, and presents with a herald patch followed by a "Christmas tree" distribution; it resolves spontaneously in 6–8 weeks. ### Management Approach ```mermaid flowchart TD A[Psoriasis diagnosis confirmed]:::outcome --> B{Severity assessment}:::decision B -->|Mild <10% BSA| C[Topical corticosteroids + emollients]:::action B -->|Moderate 10-30% BSA| D[Topical + systemic agents]:::action B -->|Severe >30% BSA| E[Biologic agents, methotrexate, acitretin]:::action C --> F[Monitor for response]:::action D --> F E --> F ``` [cite:Robbins 10e Ch 25]