Although the characteristic wedge-shaped lymphocytic infiltrate is not well demonstrated here, other features of PLC/PLEVA are seen including exocytosis of lymphocytes into the epidermis, a scaled crust (lower right), perivascular lymphocytic infiltration and vacuolar degeneration of the basilar epidermis.

Pitryiasis lichenoides et varioliformis acute (PLEVA, Mucha-Habermann disease) is characterized by a rather abrupt eruption of papules covered with a fine mica-like scale. These papules heal and leave smallpox-like (varioliform) scars. PLEVA generally affects older children and young adults. These eruptions occur mainly on the trunk, and are less than 5 mm in diameter. The papules may be scaly, crusted or vesicular. It is usually a self limited condition. Although the exact cause of PLEVA is not yet known, there is some evidence that it may be a lymphoproliferative disorder.

In a more serious form of PLEVA (febrile ulceronecrotic Mucha-Habermann disease), patients develop necrotic papules that coalesce into large crusted ulcers, blisters and papules. Systemic symptoms include fever, CNS symptoms, anemia, sepsis and even death. This form has been associated with EBV and CMV infections (Busam).

Histologically, there is focal parakeratosis with a scale crust. There is a dense infiltrate at the papillary dermis in a band-like and perivascular pattern. This lymphocytic infiltrate may also be "wedge-shaped". There is prominent lymphocytic exocytosis into the epidermis as well as vacuolar degeneration of the basal layer. One of the most characteristic findings is the presence of holes in the enlarged keratinocytes (Weems). Necrotic keratinocytes, spongiosis, vacuolar degeneration of the basal layer and extravasation of RBCs into the epidermis are variably seen (Rapini).

A milder form of PLEVA is called pityriasis lichenoides chronicus (PLC) is characterized by minimally symptomatic papules with less crusting, less neutrophilis, less spongiosis, fewer vesicles (Rapini).