New histopathologic findings in drug eruptions.

Several new findings associated with hyperpigmentation have been reported in the past decade, the most notable being amiodarone-induced hyperpigmentation, which was shown to demonstrate both a lymphocytic dermatitis as well as yellowish brown granules that can be found within several cell types. The nature of this material has not been elucidated, although the drug or one of its metabolites composes at least a portion of the granules. The nature of the clofazimine-induced hyperpigmentation was shown to be caused by the accumulation of a ceroid lipofuscin within lipid-laden macrophages. Several chemotherapy-induced clinical and histologic changes have been reported in the past decade because of new chemotherapeutic drugs, better recognition of histologic reaction patterns, and the use of higher dosages by oncologists. A unique dermatitis, cutaneous eruption of lymphocyte recovery--although not directly due to use of chemotherapeutic agents--occurs after the return of immunocompetent lymphocytes in the peripheral circulation and skin, producing a maculopapular eruption that demonstrates a nonspecific superficial perivascular dermatitis on biopsy. Another clinically specific reaction, chemotherapy-induced acral erythema, demonstrates a nonspecific histologic pattern characterized by an interface dermatitis. Specific histologic patterns were reported for reactions following use of etoposide--starburst cells--and of busulfan--large atypical keratinocytes. There have been reports of new reactions due to chemotherapeutic agents involving sweat glands: neutrophilic eccrine hidradenitis, characterized by neutrophils and necrosis; and syringosquamous metaplasia, a histologic reaction of the sweat duct characterized by squamous metaplasia. New inflammatory reaction patterns include drug-induced generalized pustular toxic erythema, which histologically shows subcorneal pustules and occasional eosinophils. Cephalosporins were reported to produce a syndrome that clinically and histologically resembles pemphigus. Naproxen is reported to produce a clinical and histologic reaction similar to porphyria cutanea tarda. Quinine and piroxicam both induce a photosensitive dermatitis that histologically shows a nonspecific spongiotic dermatitis. A histologically unique reaction pattern manifesting as a lichenoid giant cell dermatitis may be produced by use of either methyldopa or chlorothiazide. Both phenytoin and carbamazepine produce a dermatitis that histologically imitates mycosis fungoides. Finally, phytonadione injections may produce a clinical and histologic reaction that resembles morphea.