Comparative clinicopathological study on pityriasis lichenoides chronica and small plaque parapsoriasis

The term parapsoriasis refers to a group of chronic asymptomatic scaly dermatoses of unknown etiology about which there is still controversy over the nosology and nomenclature of the different conditions that comprise the group, particularly pityriasis lichenoides chronica (PLC) and small plaque parapsoriasis (SPP). In an attempt to establish the distinctive clinicopathologic features of these two dermatosis, we prospectively studied 44 patients who presented with the typical clinical and histologic picture of either of these two diseases. SPP was clinically characterized by scaly oval plaques on the trunk and proximal aspect of extremities. Spongiosis was the salient histopathologic feature, with absence of fibrosis or melanophages. PLC presented with a scaly papular eruption over the trunk and extremities and histologically was characterized by an interface dermatitis. We conclude that sufficient clinical and histologic features differentiate these two entities and we propose that the term parapsoriasis be used only to designate SPP and large plaque parapsoriasis.