Patch testing in cutaneous reactions caused by carbamazepine

The usefulness of patch testing in the diagnosis of carbamazepine-induced allergic skin eruptions was studied in 18 patients with previous histories of skin eruptions caused by carbamazepine. The etiological role of carbamazepine was ascertained by peroral or topical provocation in 15 (out of 18) patients. The clinical reactions caused by the drug were classified as maculopapular exanthema with general symptoms (7 patients), other type of exanthema (3), exfoliative dermatitis (erythroderma) (3), fixed drug eruption (3), erythema multiforme (1) and urticaria (1). Patch testing showed positive reactions to carbamazepine in 7 patients; in addition, 2 patients had doubtful reactions. Positive patch test reactions were seen only in patients with exfoliative dermatitis (all 3 patients) and maculopapular exanthema (4 out of 7). None of the patients with fixed drug eruption, erythema multiforme or urticaria, or the control subjects, had positive patch test reactions to carbamazepine. The present study suggests that patch testing is useful in the diagnosis of carbamazepine allergy in patients with maculopapular eruptions or erythrodermas.