Pityriasis lichenoides variants describe scaly dermatoses with necrotic papules that are clinically and histologically different from parapsoriasis. These diseases generally are benign and undergo spontaneous resolution.
Pityriasis lichenoides is a rare cutaneous disorder of unknown etiology. Pityriasis lichenoides encompasses a spectrum of clinical presentations ranging from acute papular lesions that rapidly evolve into pseudovesicles and central necrosis (pityriasis lichenoides et varioliformis acuta or PLEVA) to small, scaling, benign-appearing papules (pityriasis lichenoides chronica or PLC). Although historically, the term Mucha-Habermann disease has referred only to PLEVA, the term applies broadly to the entire spectrum of disease including PLC. A rare febrile ulceronecrotic variant has been reported, which is a severe form of PLEVA with high fever and marked constitutional symptoms. Lesions may self-involute and resolve completely over weeks, or new lesions occasionally may appear in crops, waxing and waning spontaneously for months to years thereafter.
Mucha-Habermann disease is not a vasculitic process despite reports of immunoglobulin and complement deposition in vessels. Fibrin is not present in the walls of vessels, and thrombi are not found in the lumen. A cell-mediated mechanism has been proposed based on a T-lymphocytic infiltrate with a cytotoxic/suppressor phenotype, diminished epidermal Langerhans cells, and a reduction of the CD4/CD8 ratio. Mucha-Habermann disease is not a lymphoproliferative disorder. CD30 (Ki-1) cells, which are associated with large cell lymphoma, have been identified in the infiltrate of both lymphomatoid papulosis and Mucha-Habermann disease, leading some authors to view this as a self-limited self-healing lymphoproliferative disease.
