Development of Agranulocytosis after Discontinuation of Methimazole: An Unusual Case

Area of Science:

• Endocrinology
• Hematology
• Pharmacology

Background:

• Agranulocytosis is a severe adverse effect of antithyroid drugs (ATDs).
• While agranulocytosis is known during continuous ATD therapy, its occurrence after treatment cessation is unusual.
• Methimazole (MMI) is a commonly prescribed ATD for hyperthyroidism.

Purpose of the Study:

• To report an atypical case of antithyroid drug-induced agranulocytosis.
• To emphasize the importance of monitoring for agranulocytosis even after ATD discontinuation.
• To highlight the clinical presentation and management of this rare adverse event.

Main Methods:

• Case report of a 41-year-old woman treated with methimazole (MMI).
• Detailed hematologic and serological evaluations were performed.
• Patient received empirical antibiotic treatment for symptoms of an upper respiratory tract infection.

Main Results:

• Agranulocytosis and upper respiratory tract infection symptoms developed three weeks after MMI discontinuation.
• No alternative cause for agranulocytosis was identified.
• The patient successfully responded to empirical antibiotic treatment, with neutropenia resolving within seven days.

Conclusions:

• This case demonstrates that antithyroid drug-induced agranulocytosis can manifest after treatment cessation.
• Physicians should maintain a high index of suspicion for agranulocytosis even after patients discontinue ATD therapy.
• Prompt recognition and management are crucial for favorable outcomes in ATD-induced agranulocytosis.