We report the case of a 32 year old female, with a family history of thyrotoxicosis, who presented with palpitations, weight loss, anxiety and diarrhoea. The patient was clinically thyrotoxic with tachycardia and tremor. On examination there was no goitre or evidence of Graves opthalmopathy. Biochemistry confirmed thyrotoxicosis with a T4 of 35 (1123 pmol/l) and a T3 of 13.3 (3.56.5 pmol/l). Urea, electrolytes and liver function tests were normal. Electrocardiogram (ECG) demonstrated left bundle branch block. Carbimazole therapy was started. Twenty-four hour electrocardiogram monitoring confirmed persistent left bundle branch block and an echocardiogram showed anteroseptal hypokinesia but was otherwise normal.
|Months of treatment||Free T4 (1123 pmol/L)||Free T3 (3.56.5 pmol/L)||TSH (0.15.5 mU/L)||Carbimazole (dose in mg per day)||ECG|
Following eleven months of treatment the patient was euthyroid with both the TSH and T4 within the normal range. Repeat ECG showed that the left bundle branch block had resolved which was confirmed on twenty-four hour cardiac monitoring. Left bundle branch block is rare in young woman. The fact that it resolved when she was euthyroid suggests Graves thyrotoxicosis as the aetiology. Reversible left bundle branch block due to thyrotoxicosis is extremely rare, with only one previous case report identified from the literature. Possible mechanisms could include an autoimmune focal myocarditis or a reversible cardiomyopathy.