About Methimazole

Methimazole, a thionamide (antithyroid medication), is used to treat hyperthyroid disorders (1,2). Thionamide-induced aplastic anemia is a life threatening side effect of this class of medication (1,2). These patients often present atypically, with concomitant infection, as well as laboratory aberrations suspicious for other immunological, infectious, or neoplastic processes. The infrequency with which this clinical consequence is encountered, combined with the often-complex presentation, makes thionamide-induced aplastic anemia a formidable diagnostic challenge, often resulting in delayed diagnosis and adverse patient outcomes.

We report a 24-year-old female who developed ANCA-MPO positive vasculopathy and concomitant febrile aplastic anemia complicated by streptococcus septicemia in the setting of Methimazole therapy.

Methimazole is one of two agents approved in the United States for the use of thyroid hormone suppression. It works by inhibiting the synthesis of thyroxine and triiodothyronine by blocking the oxidation of iodine in the thyroid gland (3,14). Methimazole is indicated for use in patients with Graves’ disease or toxic multinodular goiter for whom radioactive iodine ablation or thyroidectomy is not an appropriate treatment option (3,4).

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It is also indicated for symptom control in patients awaiting thyroidectomy or radioactive iodine ablation (3,4).

Methimazole is absorbed via the gastrointestinal tract and metabolized by the liver (4). It has been associated with numerous adverse side effects to include congenital malformations (primarily within the first trimester), hepatotoxicity, hypothyroidism, and in rare instances ANCA associated vasculitis as well as myelosuppression leading to agranulocytosis and in some, aplastic anemia (4). Aplastic anemia, typically manifested by recurrent infections, sepsis, fatigue, cardiopulmonary findings associated with anemia, mucosal bleeding, and fungal infections is a rare but potentially life threatening complication (5); therefore, it is recommended that patients be closely monitored while on Methimazole therapy (3,4).

Patients should be instructed to report to their providers any symptoms suggestive of agranulocytosis or aplastic anemia to include; sore throat, malaise, fever, or exfoliative dermatitis. Methimazole should be immediately discontinued if agranulocytosis, aplastic anemia or ANCA positive vasculitis is evident following its use (4).

A 24-year-old female, recently restarted on methimazole therapy for hyperthyroidism in the setting of Grave’s disease, presented to an emergency department secondary to symptoms of an upper respiratory infection and diarrheal illness. She was admitted to inpatient services with concern for sepsis. On admission, she was febrile and tachycardic with physical examination findings notable for a diffusely enlarged goiter and profound bilateral cervical lymphadenopathy.