Pityriasis lichenoides

     

    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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