Severe myelosuppression following alopecia shortly after the initiation of 6-mercaptopurine in a patient with Crohn's disease.

A 15-year-old, woman, Crohn's disease patient, who carried the TPMT *3C heterozygous mutant, complained of alopecia 3 days after starting 6-mercaptopurine (6-MP) and then developed severe myelosuppression 6 weeks after starting 6-MP. The alopecia involved scalp hair only (body hair preserved) and was dominant in the temporal region. Following these side effects, transient remission of Crohn's disease occurred. Myelosuppression due to 6-MP is a rare but life-threatening side effect that is difficult to predict despite continuous monitoring of complete blood cell counts. In the present case, 6-MP-induced alopecia preceded myelosuppression and progressed rapidly as the myelosuppression worsened.