Severe lymphocytopenia induced by methimazole tablets: A rare case report.

RATIONALE: Severe lymphocytopenia, febrile granulocytopenia, and leukopenia induced by methimazole (MMI) are extremely rare. PATIENT CONCERNS: A 26-year-old Han Chinese female with hyperthyroidism was admitted to the hospital with fever and tonsillar enlargement after taking MMI tablets for 1 month. Adverse drug reactions correlation analysis revealed this as a novel severe adverse reaction. DIAGNOSES: The patient was diagnosed with agranulocytosis with fever, thyroid storm, acute suppurative tonsillitis, and mild anemia. INTERVENTIONS: After admission, MMI tablets were discontinued. The patient received granulocyte colony-stimulating factor, Leucogen tablets, Diyu Shengbai tablets to elevate white blood cell count, methylprednisolone sodium succinate for inflammation, and cefuroxime sodium for infection control. OUTCOMES: The patient was discharged after 11 days of clinical treatment. LESSONS: Through the assessment of adverse drug reactions correlation and analysis of susceptibility factors, we recognized the importance of medication education and demonstrated that changes in clinical practice can save lives.