Neutropenia and Agranulocytosis Induced by Antithyroid Drugs: Clinical Insights and Management

Abstract Background: Antithyroid Drugs (ATDs) are widely used for hyperthyroidism but can rarely cause idiosyncratic neutropenia and agranulocytosis, potentially leading to life-threatening infections. Objective: To summarize the definition, epidemiology, clinical features, and management of ATD induced neutropenia and agranulocytosis. Methods: Review of international literature and local data from the University Hospitals of Strasbourg. Results: Neutropenia is classified as moderate (ANC 1000–1500/mm³), severe (<500/mm³), or profound (<200/mm³), while agranulocytosis corresponds to near-complete granulocyte depletion (ANC <100/mm³). ATD-induced neutropenia usually occurs idiosyncratically within the first three months of therapy. Early clinical signs include fever >38.5°C and erythematous or ulcero-necrotic pharyngitis, with additional manifestations such as stomatitis, gingivitis, and systemic infections in advanced cases. Local data indicate seven cases per year; international series report incidences of 0.1–0.5%, primarily within 2-12 weeks of treatment. Risk factors include age >60 years, female sex, and possibly higher initial doses. Prompt recognition and immediate complete blood count are essential, as delayed diagnosis increases the risk of bacteremia, pneumonia, and septic shock. Management involves ATD discontinuation, infection control, and consideration of Granulocyte Colony-Stimulating Factor (G-CSF). Cross-reactivity between ATDs should guide alternative therapy. Conclusion: Although rare, ATD-induced neutropenia and agranulocytosis are medical emergencies requiring early detection and adherence to international management guidelines to prevent severe outcomes.