Complete Resolution of Pityriasis Rubra Pilaris With Targeted Treatment: A Case Report.

Pityriasis rubra pilaris (PRP) is a rare inflammatory dermatosis characterized by erythematous plaques with follicular hyperkeratotic papules, presenting challenges in diagnosis and management. Here, we present a case report of a 70-year-old male with a known medical history of diabetes mellitus and hypertension who presented with a two-year history of pruritic, purple papules, plaques, and scaly lesions distributed symmetrically on the hands, chest, and legs. Histological examination confirmed PRP, revealing classic features of PRP, including broad epidermal ridges with thick suprapapillary plates and perivascular lymphocytic infiltrate in the dermis. Treatment with systemic retinoids initially provided partial improvement; however, ustekinumab, a monoclonal antibody targeting interleukin-12 and -23, led to significant clinical improvement. This case highlights the therapeutic potential of ustekinumab in refractory PRP cases and the importance of histopathological confirmation in guiding treatment decisions.