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Introduction/Clinical/Pathogenesis
Polymorphous light eruption (PMLE) is an idiopathic eruption which likely represents the combined effects of
photo-toxicity and a delayed-type hypersensitivity reaction to ultraviolet light, usually UVA, but also UVB
in some patients. Clinically, lesions are polymorphous in different individuals but appear monomorphous in
a single individual, comprising papules, vesicles or urticarial plaques that erupt thirty minutes to three
days after ultraviolet light exposure and characteristically resolve in seven to ten days following
discontinuance of sun exposure. Lesions may clinically appear eczematous or may resemble pemphigus, prurigo
nodularis, erythema multiforme or insect bite reactions, thus the epithet "polymorphous". There is a
predilection for the hands, forearms, upper arms and head and neck regions. It is a disease of temperate
climates; patients living near the equator are only rarely affected. Females are preferentially affected,
characteristically in the third decade of life, with roughly fifty percent of patients manifesting
decreasing photosensitivity over time. Other idiopathic light-induced eruptions include actinic prurigo,
actinic reticuloid, juvenile springtime eruptions, and hydroa vacciniforme.
Both polymorphous light eruption and lupus erythematosus share in common light sensitivity and at a light
microscopic level can be difficult to distinguish apart. A recent study has shown that approximately half
of lupus patients reported symptoms compatible with polymorphous light eruption which preceded the features
characteristic of lupus erythematosus. Photosensitivity is a well-known manifestation of lupus
erythematosus (LE). Conversely patients with polymorphous light eruption when followed over a 20 year
period had only a slightly increased incidence of autoimmune disease however a significant increased
incidence of lupus erythematosus could not be documented. Dietary fish oil rich in omega-3 polyunsaturated
fatty acids reportedly increases the resistance to ultraviolet-induced erythema and rash provocation in
polymorphic light eruption and hydroavacciniforme. The photoprotective effect of fish oil appears to be due
to inhibition of prostaglandin E2 production
TABLE 8
Polymorphous light eruption |
CLINICAL FEATURES |
- Erythematous, pruritic papules or papulovesicles and urticarial plaques
- Eruption occurs 30 minutes to 3 days after sun exposure, and resolves in 7-10 days
- Predilection for sun-exposed sites : hands, forearms, head and neck area
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HISTOPATHOLOGY |
- Perivascular infiltrates of lymphocytes, eosinophils and neutrophils
- Exocytosis, spongiosis, vesiculation, acanthosis and focal parakeratosis common
- Some cases show vacuolopathic interface injury pattern or no epidermal changes
- Marked papillary dermal edema classically
- Blood vessels show ectasia and endothelial swelling which preferentially affects superficial vasculature
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DIFFERENTIAL DIAGNOSIS |
Delayed-type hypersensitivity reactions including
Allergic contact reactions
Rosacea
Other photoallergic/phototoxic eruptions
Insect bite reactions
Connective tissue diseases including
Discoid lupus erythematosus
Subacute lupus erythematosus
Jessner's lymphocytic infiltrate
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Histopathology
The characteristic histomorphology of PMLE includes striking papillary dermal edema accompanied in early
lesions by a superficial perivascular lymphoid infiltrate and in late lesions by a more intense superficial
and deep infiltrate, which may show a "sleeve-like" morphology mimicking EAC.
Eosinophils, neutrophils, hemorrhage, vascular fibrin deposition and vesiculation owing either to marked
papillary dermal edema or epithelial spongiosis may be seen. The epidermis may show acanthosis and
parakeratosis, the common alteration being an eczematous one with spongiosis and vesiculation. In rare
cases, an interface dermatitis mimicking that of connective tissue disease or erythema multiforme may be
present. Juvenile springtime eruption typically shows an erythema multiforme like interface. Vascular
changes of endothelial swelling and edema, present in the superficial plexus, diminish in the depths of the
biopsy. By DIF examination there is vascular IgM and C3 deposition in the absence of a lupus band.
Differential Diagnosis
Actinic reticuloid is a pseudolymphomatous tissue reaction associated with psoriasiform lataerations of the
epidermis accompanied by a superficial lymphomatoid vascular reaction; the dermal based infiltrate includes
numerous transformed lymphocytes, sometimes associated with Pautrier microabscess formation. Multinucleated
stromal giant cells associated with intervascular fibrosis and confinement of the infiltrates to the
perivascular connective tissue is characteristic. Actinic prurigo is an entity seen dominantly in native
Americans, and shows an overlap of phototoxic, photo-adaptive, and photo-allergic features. Thus,
hypergranulosis, acanthosis, individual cell necrosis at all levels of epidermis, basilar melanocyte
activation with irregular epidermal melanization, and epidermal dysmaturation with architectural disarray
form the spectrum of epidermal changes. The infiltrates are variable within the dermis, both in terms of
density and composition. Some cases show an interface dermatitis. Biopsies of hydroa vacciniforme
characteristically show interepidermal vesiculation with reticular degeneration leading to confluent
epidermal necrosis, vascular thrombosis and a variable superficial and deep perivascular infiltrate of
lymphocytes with occasional eosinophils and, in some cases, a lobular or septal panniculitis. Lesions heal
with scarring.
The characteristic morphology of juvenile springtime eruption is an interface dermatitis with follicular
accentuation accompanied by a brisk superficial and mid-dermal angiocentric lymphocytic infiltrate with
endothelial swelling and edema. The presence of interface change in lesions of juvenile springtime
eruption, actinic prurigo, hydroa vacciniforme, and a small percentage of cases of idiopathic PMLE suggests
a pathogenetic role for cellular cytotoxicity induced by light exposure.
References
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1974; 5:25-43.
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Granter S ed's. Textbook of Dermatopathology. New York : McGraw-Hill Co, 1998:69-81.
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Philadelphia: Lippincott-Raven, 1997:
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long-term follow-up study of 94 patients. Dermatol 1998;134:1081-5
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patients with various photosensitivity dermatoses. Arch Dermatol Res 1995;287:586-90
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1998;138:173-8
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B-generated PGE2 levels in skin and increases the threshold to provocation of polymorphic light eruption. J
Invest Dermatol 1995;105:532-5
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