Pinpoint papular variant of polymorphous light eruption: clinical and pathological correlation

Abstract

Polymorphous light eruption (PMLE) is the most common chronic idiopathic photodermatosis usually manifesting as a papular eruption along with several other morphological variants including a pinpoint papular variant. Between June 1998 and August 2003, 10 PMLE patients presented to the Department of Dermatology at Henry Ford Hospital with complaints of a pruritic pinpoint papular eruption associated with sun exposure. In six patients skin biopsies were performed along with a detailed history and complete skin examination. We correlated the histology with the clinical course of disease corresponding to acute and subacute disease presentation. We also performed immunohistochemistry on three cases to study the immunophenotype in PMLE. The clinical, histologic and immunostain findings are summarized. Acute: Clinically pinpoint papules and vesicles, some with erythematous base, were seen. Histology showed focal vesicle formation, spongiosis, oedema, red blood cells extravasation, and superficial and deep perivascular and interstitial lymphocytic infiltrate with occasional eosinophils. Subacute: Clinically pinpoint papules with or without erythema were seen. Histology of the pinpoint lesion showed a nodular collection of lymphocytes and histiocytes with claw-like extension of epidermal rete ridges at the lateral boundaries of the lesion. Overlying epidermal atrophy with adjacent spongiosis, exocytosis, oedema and a superficial perivascular lymphocytic infiltrate and parakeratosis was also observed. The histologic differential diagnosis included lichen nitidus. Immunohistochemical stains revealed the following results: CD8, CD68 positive, CD4 variable (strongly positive to negative) and S-100 negative. (i) Pinpoint papular variant of PMLE is a distinct entity, which shows characteristic histology corresponding to the clinical course of the disease (acute and subacute). (ii) The histologic and immunophenotypic differential diagnosis of this variant during the subacute phase includes lichen nitidus.