CONTACT PHOTOALLERGY TO TRIBROMSALICYLANILIDE
SUMMARY. .
Photoallergy. A review.
Photoallergy can be defined as an acquired altered reactivity of the skin presumably dependent on the development of circulation antibodies or cell-mediated immune responses. In contrast to phototoxic reactions, photoallergic responses are uncommon and consist clinically of immediate urticarial or delayed papular and eczematous lesions. Histologically the immediate responses show dermal edema and vasodilatation. The delayed reactions are characterized primarily by perivascular round-cell infiltrates in the dermis. Photoallergy can be induced by exogenous photosensitizers which may arrive at the skin through contact or systemic pathways and the reactions are delayed in nature. Photoallergy not related to exogenous photosensitizers may be immediate (solar urticaria) and possibly delayed (polymorphous light eruptions) in nature.
CONTACT PHOTODERMATITIS FROM BITHIONOL.
Patients with contact photodermatitis from bithionol fall into two groups: (a) Transient contact reactors with normal MED. * (b) "Persistent light reactors" with lowered MED and positive WGT. Patch tests to bithionol are usually negative but photopatch tests to bithionol are positive and eczematous. Photosensitivity occurs not only from exposure to the usual sunburn spectrum, but also to longer wavelengths of light as demonstrated by reactions through window glass. Red veterinary petrolatum is an effective sunscreen, preventing both the ordinary sunburn and burning from wavelengths of light above 3,200 angstroms. Parenteral use of psoralens and subsequent sunlight exposure can convert the lowered MED to normal range.