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

Explanation

## Diagnosis: Chronic Plaque Psoriasis ### Clinical Presentation The patient presents with classic features of chronic plaque psoriasis: - Well-demarcated erythematous plaques with silvery-white scale - Predilection for extensor surfaces (elbows, knees) - Scalp involvement - Seasonal variation (worse in winter, better in summer) - Positive Auspitz sign (pinpoint bleeding when scale is removed) ### Key Diagnostic Features **Key Point:** Chronic plaque psoriasis is the most common form, accounting for ~90% of all psoriasis cases. It is characterized by symmetric distribution on extensor surfaces and scalp. **High-Yield:** The Auspitz sign (punctate bleeding after scale removal) and Koebner phenomenon (lesions appearing at sites of trauma) are pathognomonic for psoriasis. ### Distinguishing Features from Differentials | Feature | Chronic Plaque Psoriasis | Pityriasis Rosea | Lichen Planus | Seborrheic Dermatitis | |---------|------------------------|-----------------|---------------|---------------------| | Scale | Silvery-white, adherent | Fine, collarette | Violaceous, thin | Greasy, yellowish | | Distribution | Extensor surfaces, scalp | Trunk, proximal limbs | Wrists, genitals, mucosa | Scalp, face, intertriginous | | Seasonal | Worse in winter | Acute onset, self-limited | No seasonal pattern | Worse in winter | | Auspitz sign | Positive | Negative | Negative | Negative | | Duration | Chronic, relapsing | Self-limited (6–8 weeks) | Chronic | Chronic | **Clinical Pearl:** Seasonal exacerbation in winter is a hallmark of psoriasis, thought to be related to decreased UV exposure and immune dysregulation in cold weather. ### Pathophysiology Psoriasis is a T-cell-mediated autoimmune disorder with: 1. Th1 and Th17 cell infiltration into dermis and epidermis 2. Increased epidermal proliferation (turnover time: 3–4 days vs. normal 28 days) 3. Parakeratosis and acanthosis on histology 4. Dilated capillaries in dermal papillae (responsible for Auspitz sign) **Mnemonic:** **PORES** for psoriasis features: - **P**laques (well-demarcated) - **O**wl-eye appearance (on histology) - **R**ed (erythematous) - **E**xtensor surfaces (predilection) - **S**ilvery scale ### Management Approach For mild-to-moderate plaque psoriasis: - Topical corticosteroids (first-line) - Topical calcineurin inhibitors - Vitamin D analogues - Coal tar preparations - Phototherapy (UVB, PUVA) for extensive disease [cite:Fitzpatrick's Dermatology in General Medicine 9e Ch 8]