Carbimazole‑induced agranulocytosis

A 47 year old lady with hyperthyroidism for past 1½ years was initially on Carbimazole 20 mg orally then changed to 30 mg (during Hysterectomy) but was taking 10 mg for last 1 year. She had intermittent fever with severe B/L bifrontal headache since 3 weeks. Routine investigations showed anaemia, neutropenia, leucopenia and CRP elevation. Peripheral smear showed normocytic normochromic anaemia with Rouleaux formation, leucopenia with 2% atypical cells and mild thrombocytosis. Widal test, RA factor (Rheumatoid factor) test, Ig M (Immunoglobulin M) dengue, Ig M Lepto, TORCH infections (Toxoplasmosis, Other (Syphilis, varicella‑zoster, parvovirus B19), Cytomegalovirus and Herpes infections), ANA (Antinuclear antibody) screen cANCA (Cytoplasmic antineutrophil cytoplasmic antibodies) and pANCA (Perinuclear Anti‑Neutrophil Cytoplasmic Antibodies) tests were negative. Bone marrow aspiration showed normo to hypercellular marrow with 15% atypical cells and plasma cells. Multiple myeloma workup was done. Carbimazole was withheld. Conclusion: Drug induced agranulocytosis occurs with in 1‑2 months of taking the antithyroid medication but onset delayed by 1½ year. De‑challenge resulted normalization of blood parameters.