Endocrine Abstracts

Introduction: Carbimazole is the first drug of choice for treating thyrotoxicosis. We report a case of an Asian gentleman recently started on carbimazole for thyrotoxicosis who complained of severe generalised muscle pain and weakness.

Report: A sixty-four year old gentleman was diagnosed with thyrotoxicosis (TSH <0.01 mU/l, Free T₄=40 pmol/l, Free T₃=14.9 pmol/l) in the month of July 08 and was started on carbimazole 40 mg daily. He also suffered from ischaemic heart disease and depression but had not started any other medication recently. Repeat thyroid function testing in September revealed biochemical recovery (TSH < 0.01 mU/l, Free T₄=16.5 pmol/l). However, the patient was admitted to hospital with a history of increasing generalised muscle pain and tiredness, which he reported started a few days after the commencement of carbimazole in July. The patient became so weak with severe muscle pain that he was unable to mobilise. Blood results on admission revealed a raised creatinine phosphokinase (CPK) =1213 U/l, low calcium =2.03 mmol/l, and raised Alkaline Phosphotase =406 U/l. Test for myoglobulinuria was negative. Thyroid function test (TSH =0.01 mU/l, Free T₄=16.1 pmol/l) were compatible with adequate control of thyrotoxicosis. Carbimazole was stopped on admission and the patient’s symptoms improved gradually. He was discharged from hospital with a view to discussing alternative treatment for his thyrotoxicosis. His CPK and calcium values gradually returned to normal over a next four weeks.

Conclusion: Although a reported rare side effect of thionamides, patients need to be informed of this potentially severe side effect, which rapidly improves once carbimazole or propylthiouracil is stopped.