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Patients with antithyroid drug–induced agranulocytosis may have normal white blood cell counts
The background of the study. Agranulocytosis (very
low white blood cell [WBC] count) is the major life-threatening
side effect of the antithyroid drugs given to patients with hyperthyroidism,
because it predisposes them to infection. This retrospective study
describes the clinical and hematologic findings in a large group
of patients with agranulocytosis.
How the study was done. From 1975 to 2001, 30,798 patients (23,646 women, 7152 men) with hyperthyroidism were treated with an antithyroid drug at a clinic in Japan. WBC counts were done biweekly for the first two months of therapy and monthly hereafter. Therapy was stopped when agranulocytosis, defined as a granulocyte count of <0.5x109/liter, was detected. Starting in 1990, patients with agranulocytosis were treated with granulocyte colony-stimulating factor (G-CSF).
The results of the study. During the study period, 109 patients (0.35 percent) had agranulocytosis (103 women, 6 men; mean age, 40 years). Ninety-three patients were among the 26,425 patients (0.4 percent) given methimazole, and 16 were among the 4373 patients (0.4 percent) given propylthiouracil. Among these 109 patients, 50 were found to have agranulocytosis on routine testing. The drug was stopped, and they never had symptoms of infection. The other 59 patients had symptomatic agranulocytosis; all recovered.
At the time of diagnosis of agranulocytosis, the WBC count was >3.0x109 cells/liter (normal, 4.5 to 10x109) in 18 of the 109 patients (16 percent), and it was ≥4.0x109 cells/liter in 5 patients. During therapy, 670 patients (2 percent) had a WBC count of <3.0x109cells/liter and 3347 patients (11 percent) had a WBC count of 3.0 to 3.9x109 cells/liter, but no agranulocytosis, on at least one occasion.
The conclusions of the study. Some patients with hyperthyroidism treated with methimazole or propylthiouracil have agranulocytosis despite having a total WBC count ≥3.0x109 cells/liter.
The original article. Tajiri J, Noguchi S. Antithyroid drug-induced agranulocytosis: special reference to normal white blood cell count agranulocytosis. Thyroid 2004;14:459-62.
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| Thyroid Digest Index | | | November 2004 Thyroid Digest |
