Red Scaly Patches

Abstract

Differential diagnosis of scaly, red patches includes thin psoriasis, pityriasis rubra pilaris (PRP), mycosis fungoides (MF), MF-like drug eruption, and parapsoriasis.

Psoriasis and PRP share some histological findings (acanthosis and hyperparakeratosis) but may be differentiated in most cases. Neutrophils in the parakeratosis or the granular layer, significant loss of granular layer, tortuous capillaries in dermal papillae, and atrophy of the suprapapillary epidermis, all speak strongly for psoriasis. Parakeratosis alternating with orthokeratosis in both planes in the stratum corneum favors PRP.

Single or grouped lymphocytes with clear halos in the epidermis or only the basal layer with no spongiosis, is characteristic of MF. MF-like drug eruption, also known as lymphomatoid drug eruption, may be suspected in cases with features intermediate between patch MF and subacute spongiotic dermatitis, both, clinically and/or histologically.