Myasthenic crisis caused by azathioprine-induced fever

Azathioprine is an established immunosuppressive agent in the treatment of myasthenia gravis. In rare cases, complications such as hypersensitivity reactions including fever may occur. A 73-year-old patient with the first manifestation of myasthenia gravis was immunosuppressed with azathioprine and prednisolone in addition to pyridostigmine treatment and discharged from hospital without symptoms. Ten days after onset of azathioprine therapy, he developed fever and a myasthenic crisis requiring artificial ventilation. Azathioprine was discontinued. Microbiological and radiological examinations revealed no signs of infection. After clinical improvement azathioprine was re-started, and following a single dose the patient again presented with fever and tachycardia. Azathioprine was discontinued, and all symptoms abated within a day. These symptoms were most probably caused by an azathioprine-induced hypersensitivity reaction. Life-threatening myasthenic crises may occur if such a hypersensitivity reaction remains unrecognized in patients with myasthenia gravis.