Pityriasis lichenoides

Editor: unassigned

A self-limited inflammatory dermatosis of unknown etiology. Subclassified into acute (pityriasis lichenoides et varioliformis acuta, PLEVA) and chronic (pityriasis lichenoides chronica, PLC) forms:

Pityriasis lichenoides et varioliformis acuta (PLEVA):

Clinical Features:

Generalized eruption of lesions of varying ages which progress as follows: papule, central vesiculation, pustulation, erotion with ulceration, crusting and eventual healing with scar formation
Predilection for flexural surfaces
Systemic symptoms may occur.
More common in children and young adults

Histologic Features:

Parakeratotic scale, often containing neutrophils
Interface change with necrosis of basal keratinocytes
Marked upper and deep dermal perivascular lyphocytic inflammation (predominantly CD4+ T-cells)
Frequently marked exocytosis of lymphocytes into the epidermis
Fully developed lesions may show dermal and epidermal hemorrhage along with endothelial cell swelling and rarely vasculitis.
Older lesions show confuent necrosis of keratinocytes and eventual vesicle formation, ulceration and granulation tissue, terminating with dermal scar formation.

Pityriasis lichenoides chronica (PLC):

Clinical Features:

Generalized, chronic, small erythematous papules that evolve to form a pinpoint dusky center
Lesions persist for several weeks, then heal without scarring.
May evolve from PLEVA or arise de novo.

Histologic Features:

Parakeratotic scale, rare necrotic keratinocytes, mild basal vacuolization (changes less pronounced than in PLEVA)
Upper dermal perivascular lymphocytic infiltrate with exocytosis of lymphocytes into the epidermis
Upper dermal and epidermal hemorrhage

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