Lack of association between thyroid function and mitral valve prolapse in Graves' disease.

1. To determine whether the association between mitral valve prolapse and Graves' disease is related to thyroid function, three groups of individuals were studied: 16 patients with Graves' disease and hyperthyroidism (hyperthyroid: T4 greater than 11.5 micrograms/100 ml), 16 patients with Graves' disease without hyperthyroidism (euthyroid: T4 less than 11.5 micrograms/100 ml), and 40 healthy individuals. The three groups were similar in age, sex distribution, and anthropometrical characteristics. 2. All patients were evaluated clinically and by M-mode and two-dimensional echocardiography to determine the presence of mitral valve prolapse. 3. The frequency of mitral valve prolapse was similar in the hyperthyroid (31%) and euthyroid patients (25%), but was higher than in the normal individuals (5%). The frequency of systolic murmur was higher in the hyperthyroid patients (75%) than the euthyroid patients (19%) or the normal subjects (0%); however, the presence of a murmur was not associated with mitral valve prolapse. Hyperthyroid (13%) and euthyroid (13%) patients had a higher frequency of clicks than the normal individuals (0%), and the presence of click was associated with mitral valve prolapse. 4. Although patients with Graves' disease have a higher frequency of mitral valve prolapse, this is not associated with thyroid function. The presence of a click but not the presence of a systolic murmur may be a clinical indicator of mitral valve prolapse in Graves' disease.