Azathioprine hypersensitivity mimicking an acute exacerbation of dermatomyositis.

We describe an unusual hypersensitivity reaction to azathioprine occurring in a patient with dermatomyositis, in which the acute manifestations suggested an exacerbation of the patient's underlying disorder. However, laboratory studies were not consistent with an acute exacerbation of dermatomyositis, and the subsequent clinical course confirmed the impression that the patient's symptoms were due to hypersensitivity to azathioprine. Physicians should be aware that a hypersensitivity reaction to azathioprine may mimic a flare of dermatomyositis.