A 38-year-old man from Delhi presents with a 6-month history of well-demarcated erythematous plaques with silvery-white scales on his elbows, knees, and scalp. He reports that the lesions worsen in winter and improve in summer. On examination, positive Auspitz sign is elicited. He denies any joint pain or systemic symptoms. His family history is significant for similar skin disease in his father. What is the most likely diagnosis?

Explanation

## Diagnosis: Chronic Plaque Psoriasis ### Clinical Presentation The patient presents with the classic features of chronic plaque psoriasis: - Well-demarcated erythematous plaques with silvery-white scales - Predilection sites: extensor surfaces (elbows, knees) and scalp - Seasonal variation (worse in winter, better in summer) - Positive Auspitz sign (pinpoint bleeding when scale is removed) - Family history of psoriasis - Absence of systemic involvement ### Key Diagnostic Features **Key Point:** Chronic plaque psoriasis accounts for 80–90% of all psoriasis cases and is characterized by symmetrical distribution on extensor surfaces. **High-Yield:** The Auspitz sign (pinpoint bleeding from removal of scale) and Koebner phenomenon (lesions appearing at sites of trauma) are pathognomonic for psoriasis. ### Pathophysiology Psoriasis involves: 1. Th1/Th17-mediated immune response 2. Increased epidermal cell turnover (cell cycle reduced from 28 days to 3–4 days) 3. Parakeratosis and acanthosis on histology 4. Dilated capillaries in dermal papillae ### Differential Diagnosis Table | Feature | Chronic Plaque Psoriasis | Pityriasis Rosea | Lichen Planus | Seborrheic Dermatitis | | --- | --- | --- | --- | --- | | **Scale character** | Silvery-white, adherent | Fine, collarette | Wickham striae | Greasy, yellowish | | **Distribution** | Extensor surfaces, scalp | Trunk (Christmas tree) | Flexor surfaces, oral mucosa | Scalp, face, intertriginous | | **Auspitz sign** | Positive | Negative | Negative | Negative | | **Seasonal pattern** | Winter exacerbation | Self-limited, 6–8 weeks | No seasonal pattern | Worse in winter | | **Family history** | Often positive | Negative | Negative | Negative | | **Systemic involvement** | Arthritis in 10–15% | None | None | None | **Clinical Pearl:** Scalp involvement with silvery scale and family history strongly favors psoriasis over other papulosquamous disorders. ### Management Approach For mild-to-moderate plaque psoriasis: - Topical corticosteroids (Class III–IV potency) - Topical calcineurin inhibitors (for face/intertriginous areas) - Vitamin D analogues (calcipotriol) - Phototherapy (UVB, PUVA) for extensive disease - Systemic agents (methotrexate, acitretin, biologics) for severe/refractory disease **Mnemonic: PLAQUES** — Plaque morphology, Location (extensor), Auspitz sign, Quantified Koebner, Usual family history, Exacerbation in winter, Silvery scale