Parapsoriasis

In dermatology, parapsoriasis is "the term applied to a group of relatively uncommon inflammatory, maculopapular, scaly eruptions of unknown etiology and resistant to conventional treatment. Eruptions are both psoriatic and lichenoid in appearance, but the diseases are distinct from psoriasis, lichen planus, or other recognized dermatoses."

Classification
There are two subgroups of parapsoriasis.

Pityriasis lichenoides
Pityriasis lichenoides is "a subgroup of parapsoriasis itself divided into acute and chronic forms."

Acute pityriasis lichenoides is "the acute form is characterized by the abrupt onset of a generalized, reddish-brown, maculopapular eruption. Lesions may be vesicular, hemorrhagic, crusted, or necrotic. Histologically the disease is characterized by epidermal necrolysis." The acute form is also called pityriasis lichenoides et varioliformis acuta (PLEVA) and Mucha-Habermann Disease.

Pityriasis lichenoides chronica is the chronic form which "shows milder skin changes with necrosis."

Parapsoriasis en plaques
The parapsoriasis en plaques subgroup includes small- and large-plaque parapsoriasis.