Endocrine Abstracts

A 59 yr old man was admitted with sweating, tremors and generalized weakness. Blood tests showed FT4>100 pmol/l, FT3>50 pmol/l, TSH<0.01 mU/l, neutrophils 0.6×10⁹ /l Past medical history included recurrent hyperthyroidism, type 2 diabetes mellitus, and neutropenia of ‘unknown’ origin(under investigation by haematology). Carbimazole 20 mg BD was started 2 days prior to admission by his general practitioner.

The neutrophil count 4 months prior to initiation of carbimazole was 1.0. Treatment with high dose carbimazole was continued under close observation, in spite of the neutropaenia. Intravenous steroids and oral propranolol were administered too. Over the subsequent days, the neutrophil count rose to 2.8×10⁹ /l (on day 5) and his symptoms improved significantly. The patient was discharged home a week later, with an outpatient referral for radioiodine ablation.

Thionamides are known to cause reversible neutropenia in 0.2%–0.5% of cases, usually in first three months although it can occur anytime. The mechanism is immune mediated destruction of circulating neutrophils by drug-dependent or drug-induced antibodies. Thyrotoxicosis itself lowers the neutrophil count in 5%–16% of patients believed to be predominantly via a humoral mechanism. Neutrophil count tends to improve as the thyrotoxicosis subsides, as shown in a retrospective series in the literature (N Aggarwal et al. BES 2014).In another recent prospective series, a third of neutropenic patients coming to a haematology clinic were found to be hyperthyroid. Our case is unique, as the patient was already known to have borderline neutropenia for several years. After the initiation of Carbimazole, the neutrophil count dropped further, to their lowest recorded level in his case. An analysis of the neutrophil count in relation to the thyroid status over the past decade showed our patient’s neutrophils improved when he was euthyroid with or without carbimazole. A decision was therefore taken to continue carbimazole (under close monitoring) to good result. Other treatment options (potassium iodide) were considered and reserved as an alternative if neutropenia failed to improve.