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.