Pityriasis rubra pilaris with acantholysis.

Two patients developed a papulosquamous eruption in a widespread distribution which progressed with islands of sparing of uninvolved skin characteristic clinically of adult-onset pityriasis rubra pilaris (PRP). Biopsies from both patients showed multiple areas of nonfollicular and follicular suprabasilar and intra-epidermal acantholysis with minimal dyskeratosis. They also showed the usual histologic features of PRP with a thickened orthokeratosis and parakeratosis, a retained and sometimes thickened granular cell layer, and psoriasiform epidermal hyperplasia with a perivascular lymphohistiocytic infiltrate in the superficial dermis. Two previous patients with PRP have been reported with nonfollicular, focal acantholytic dyskeratosis and both were interpreted as most likely representing an incidental finding. We believe the acantholysis in these two cases is related to the disease process, and in our second patient, was helpful in establishing the diagnosis.