pityriasis lichenoides et varioliformis acuta

PITYRIASIS LICHENOIDES ET VARIOLIFORMIS ACUTA

This is also known as Mucha-Habermann disease. Multiple papules, papulosquamous lesions, and papulonecrotic lesions occur. The disease is usually self limited.

Some of the papulonecrotic lesions may be hemorrhagic, and, possibly for this reason, this disease is often placed in the chapter for vasculitic diseases. Some authors go so far as to invoke 'lymphocytic vasculitis' which is probably more inferred from the clinical findings than from direct evidence of vascular damage by lymphocytes. The real damage appears to be secondary to a lymphocyte attack on the epidermis.

The most diagnostic findings are found in the epidermis and at the dermoepidermal junction. Vacuolar change at the dermoepidermal junction is characteristic, and frequently is severe. Lymphocytic exocytosis without concomitant spongiosis, as can also be seen in mycosis fungoides, is often noted. One of the most characteristic findings is the presence of holes in the enlarged keratinocytes. Parakeratosis, polymorphonuclear leukocytes in the stratum corneum, and apoptotic keratinocytes are variably present. Extravasated red blood cells within the epidermis are given diagnostic importance in some texts, but these are neither specific nor necessary for the diagnosis. Dermal lymphocytic infiltrates are perivascular and may be found in the superficial dermis and mid reticular dermis.

There are cases wherein the lesions persist, and these retain many of the pathologic features mentioned above. Such cases can be referred to as pityriasis lichenoides chronica. These should not be confused with lesions that look more like pityriasis rosea pathologically which also have been assigned to this category.

Low power view. The keratinocytes are enlarged . Most of the lymphocytes in the dermis, with the exception of those at the dermoepidermal junction, are in a perivascular distribution.

High power view of above. Focal parakeratosis is noted, and a few necrotic (apoptotic) keratinocytes are seen. Holes are found in many of the keratinocytes. Some of these holes contain lymphocytes. Lymphocytic exocytosis is prominent, and there is vacuolar change in the lower epidermis.

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	Low power view. The keratinocytes are enlarged . Most of the lymphocytes in the dermis, with the exception of those at the dermoepidermal junction, are in a perivascular distribution.
	High power view of above. Focal parakeratosis is noted, and a few necrotic (apoptotic) keratinocytes are seen. Holes are found in many of the keratinocytes. Some of these holes contain lymphocytes. Lymphocytic exocytosis is prominent, and there is vacuolar change in the lower epidermis.