Reversible dilated cardiomyopathy due to thyrotoxicosis

Whether hyperthyroidism can cause a dilated cardiomyopathy remains controversial. It has been generally accepted that thyrotoxicosis may be associated with high output heart failure and may precipitate ischemia or heart failure in patients with either symptomatic or asymptomatic underlying heart disease. However, evidence for the development of a dilated cardiomyopathy in otherwise normal hearts is confined to animal models and the pediatric population.¹ Studies showing a decreased cardiac reserve on exercise by nuclear cardiographic studies are often quoted as evidence of occult myocardial dysfunction in hyperthyroid patients. The number of patients in these studies was small and predominantly female (15 of 19).^2,3 The fact that women do not consistently increase their ejection fraction with exercise⁴ challenges the current interpretation of these results. We present a patient in whom thyrotoxicosis was accompanied by a reversible dilated cardiomyopathy.