Pityriasis rubra pilaris (PRP) is a papulosquamous disorder. The PATHOGNOMONIC clinical hallmark is:

• A Silvery micaceous scales on extensor surfaces
• B Islands of normal skin within generalised erythroderma (nappes claires) ✓
• C Target lesions with mucosal erosions
• D Koebner phenomenon on traumatised sites

Explanation

The pathognomonic feature of pityriasis rubra pilaris is the presence of islands of spared normal skin (nappes claires or 'clearings') within the background of generalised orange-red erythroderma. This distinguishes PRP from other causes of erythroderma. Additional features include follicular keratotic papules on the dorsum of fingers (Besnier's sign), palmoplantar keratoderma ('waxy' keratoderma), and cephalocaudal spread. Silvery scales and Koebner phenomenon are features of psoriasis; target lesions with mucosal erosions indicate erythema multiforme/SJS.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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