Agranulocytosis is a rare and critical adverse effect of
antithyroid drugs (ATD). The occurrence of
agranulocytosis in continuous ATD treatment patients is well known; however, a case of ATD
agranulocytosis occurring following the discontinuation of
methimazole (MMI) treatment is not a usual situation. We herein describe a case of a 41-year-old woman who was previously administered
methimazole (MMI) for ten days and developed ATD-induced
agranulocytosis and symptoms of an
upper respiratory tract infection after three weeks following discontinuation of MMI treatment. A thorough hematologic and serological evaluation did not disclose an alternative cause for the
agranulocytosis. After receiving empirical
antibiotic treatment, she responded successfully with clinical improvement of her symptoms and resolved
neutropenia on the seventh day. This case is atypical because
agranulocytosis developed after discontinuation of MMI, which strengthens the importance of remaining alert for signs of
agranulocytosis even after discontinuation of ATD treatment.