Answer of Dermatopathology Case 84

Polymorphous Light Eruption

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Abstracts

Polymorphous light eruption.Photodermatol Photoimmunol Photomed.2008 Jun;24(3):155-61.

Polymorphous light eruption is the most common photodermatosis, with a prevalence of as high as 10-20% in Western Europe and in the USA. It starts during the second and third decades of life. Although not life-threatening it can severely impair the quality of life, in particular during leisure activities and in outdoors workers. Polymorphous light eruption belongs to the group of so-called idiopathic photodermatoses. This term denotes dermatoses that occur in otherwise healthy individuals from exposure to sunlight or artificial light without the intervention of an exogenous photosensitizing agent. These diseases have two factors in common: they are precipitated by ultraviolet or visible radiation; and their exact pathomechanism remains obscure but is presumably immunologic in nature.

Marked papillary dermal edema--an unreliable discriminator between polymorphous light eruption and lupus erythematosus or dermatomyositis. J Cutan Pathol. 2010 Apr;37(4):416-25.

BACKGROUND: The clinical differential diagnosis of photo-distributed papules and plaques includes polymorphous light eruption (PMLE) and lupus erythematosus (LE). These entities share many histopathological features. However, in most contemporary textbooks, a broad band of papillary dermal edema is reported to be characteristic of PMLE and not seen in LE. Nonetheless, older reports describe papillary dermal edema in LE, including acute cutaneous LE (ACLE) in patients with systemic LE (SLE) and early lesions of discoid lupus erythematosus (DLE). Older reports also describe papillary dermal edema in microscopic sections of dermatomyositis (DM).
METHODS: Retrospective review.
RESULTS: Nine cases of LE (including two patients with acute lesions of SLE, six with DLE and one unclassifiable) and three cases of DM were identified in which sections showed striking papillary dermal edema. Attributes of chronicity, such as epidermal atrophy, follicular plugging and basement membrane thickening, were present concurrently in many sections.
CONCLUSIONS: Marked papillary dermal edema does not reliably distinguish PMLE from LE as it can be seen in ACLE, early and late lesions of DLE and DM. This phenomenon has been underemphasized in recent reports and textbooks. Furthermore, papillary dermal edema in chronic lesions of DLE has not been previously reported.

Pinpoint papular polymorphous light eruption in Asian skin: a variant in darker-skinned individuals. Photodermatol Photoimmunol Photomed. 2009 Apr;25(2):71-4.

BACKGROUND: Polymorphous light eruption (PMLE) is the most common idiopathic but probably immunologic photodermatosis and has wide morphological variants.
METHODS: The photobiological features of all patients diagnosed with the pinpoint papular variant of PMLE at a tertiary dermatology centre in Singapore over a five-year period were retrospectively examined.
RESULTS: Twenty-one patients were reviewed from 2003 to 2007. There were 11 (52.4%) Chinese, four (19%) Malays, five (23.8%) Indians and one (4%) Cambodian. 14 (66.7%) were males and seven (33.3%) were females. The face/neck (48%) and arms/forearms (95%) were most often affected. Nineteen (90.5%) had Fitzpatrick skin phototype IV and two (9.5%) had skin phototype V. Six (28.6%) had decreased minimal erythema dose (MED) to ultraviolet B (UVB) light only, one (4.8%) had decreased MED to ultraviolet A (UVA) light only and one had decreased MED to both UVA and UVB. Four patients had photoprovocation test done, of which three had positive testing to UVA and one had negative testing to both UVA and UVB. Two histological subtypes were found in our patients, one showing perivascular dermatitis and the other consistent with lichen nitidus.
CONCLUSION: Our data suggest that pinpoint papular PMLE is not uncommon in darker-skinned individuals in our cohort.

Pinpoint papular variant of polymorphous light eruption: clinical and pathological correlation. J Eur Acad Dermatol Venereol.2006 Apr;20(4):406-10.

BACKGROUND: 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.
METHODS AND MATERIALS: 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.
RESULTS: 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.
CONCLUSION: (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.