Endocrine Abstracts

Introduction: Antithyroid drugs-induced neutropenia can occur in up to 0.5% of patients with Grave’s disease receiving ATDs. However, thyrotoxicosis-associated neutropenia has been seldomly reported. We describe a case of severe neutropenia (neutrophils <0.5) induced by florid thyrotoxicosis.

Case history: A 33-year-old lady was reviewed in endocrinology clinic following a year of palpitations, dizziness and diarrhoea. TSH <0.05mIU/L and FT4 was 92 pmol/l. WCC was 2.4 and neutrophils 1.08 with platelets of 73. Anti-TPO antibodies were positive. Carbimazole 40 mg was commenced and as FT4 reduced to 13 pmol/l, WCC improved to 5.8, neutrophils 3.4 and platelets 140 after 4 weeks. Carbimazole dose was reduced to 20 mg/day. Three weeks later, she developed cough. She was thyrotoxic (FT4=47 pmol/l, TSH <0.05mIU/l) with evidence of bone marrow suppression (WCC 3.1, neutrophils 1.1 and platelets 106). Carbimazole was stopped following haematology advice. Two weeks later, she was admitted to hospital with severe thyrotoxicosis (FT4=132 pmol/l, TSH <0.05mIU/l). WCC was 1.5 and neutrophil 0.2 with platelets of 66. She developed Moraxella in sputum and treated with antibiotics. Carbimazole was restarted at 60 mg/day. Over the following 2 weeks, bone marrow suppression completely resolved. She was not keen on surgery and had a young child, and therefore, continued on Carbimazole.

Discussion: Thyrotoxicosis-associated neutropenia has been reported in about 10% of cases. Excessive thyroid hormones levels can reduce the proliferation of haematopoietic cells. Additionally, autoimmunity might shorten the survival of neutrophils via anti-TRab mediated effect on neutrophil TSH receptors. This case highlights the importance of recognising thyrotoxicosis-associated neutropenia and considering definitive treatment of thyrotoxicosis.

Learning points: Neutropenia can be a sign of new onset hyperthyroidism and is not always due to treatment. Neutropenia should not be regarded as contraindication to starting ATDs. WBC count should be assessed prior to starting ATDs.