Cortical blindness in a 35-year-old man.

significantly during exercise. Most patients are treated early for thyrotoxicosis due to other symptoms and this abnormality goes undetected unless specifically sought for. A few patients, particularly in the older age group, may present with predominant cardiac symptoms and a picture of dilated cardiomyopathy with or without atrial fibrillation and history of significant weight loss. The cause of this cardiomyopathy is not clear. Either thyrotoxicosis lowers the threshold for development of cardiomyopathy or it may be a direct effect of increased thyroid hormone. It is important to appreciate that thyrotoxicosis can lead to dilated cardiomyopathy which is partly or fully reversible. Idiopathic dilated cardiomyopathy is very common. But before diagnosing such a disease which has no definitive treatment and a dismal prognosis one must make a sincere effort to find any treatable cause that can masquerade as dilated cardiomyopathy.