Severe neutropenia as an adverse effect of methimazole in the treatment of hyperthyroidism

Ms. K., a white, 47-year-old female with a history of hyperthyroidism had been treated with methimazole daily for a period of 9 years. She presented with a 2-day history of fever higher than 103 degrees F and cellulitis of the right arm after a scratch injury. White blood cell count (WBC) was noted at 0.4 x 10(3)/microL and neutrophils at 5.6%, indicating agranulocytosis. Methimazole was discontinued by the patient with the onset of symptoms. Appropriate intravenous antibiotic therapy and reverse isolation were provided in the acute-care setting, as well as administration of the granulocyte colony-stimulating factor (G-CSF) filgrastim. No recovery of the granulocyte count or improvement of clinical condition was noted until her sixth day of admission, at which time her WBC increased to 2.6 x 10(3)/microL. The administration of intravenous antifungals and antibiotics prevented overwhelming sepsis, while giving the G-CSF the opportunity to stimulate growth of granulocytes to finally fight the offending organisms and save this patient.