Pityriasis lichenoides and lymphomatoid papulosis.

The clinical features, histopathology, immunopathology, and management of pityriasis lichenoides and lymphomatoid papulosis are discussed, with particular emphasis on the pediatric aspects of these conditions. The difficulties in logically separating pityriasis lichenoides into an acute (pityriasis lichenoides et varioliformis acuta) and a chronic (pityriasis lichenoides chronical) form are addressed. The development of lymphoreticular malignancy in patients with lymphomatoid papulosis has been well documented, but pityriasis lichenoides has characteristically been regarded as a benign condition. However, recent reports of the development of large plaque parapsoriasis in patients with pityriasis lichenoides have led to a reconsideration. Some of these patients were in the pediatric age group. Although there are significant clinical, histopathological, and immunopathological differences between pityriasis lichenoides and lymphomatoid papulosis, the demonstration of similar clonal T cell receptor gene rearrangements and the confirmation of the potentially premalignant nature of both suggests that there may indeed be an interrelationship between these two controversial entities. Close follow-up of patients with both of these conditions is recommended, with observation being discontinued only when the patient has been free of lesions for several years.