Masked Thyroid Dysfunction in Elderly Patients With Atrial Fibrillation

To the Editor.  —We read with interest the article by Cobler et al¹ in the September Archives. We recently studied masked thyroid dysfunction in 72 elderly patients with atrial fibrillation (40 men, 32 women; mean age, 75.6 years). Patients with mitral stenosis and apparent thyroid disease were excluded from our study. Thyroid dysfunction was diagnosed by determinations of triiodothyronine (T₃) and thyroxine (T₄) radioimmunoassay levels, T₃ resin ratio, thyrotropin (thyroidstimulating hormone [TSH]) level, and TSH response to 250 μg of intravenous thyrotropin-releasing hormone (TRH). If hyperthyroidism was suspected, an iodine 123 uptake test or a thyrotropin-binding-inhibitory immunoglobulin assay or both were carried out. A TRH stimulation test was also performed in 30 age-matched controls without atrial fibrillation. None of the controls had an abnormal TRH-stimulated TSH response. In patients with atrial fibrillation, hyperthyroidism was found in five cases (6.9%), while hypothyroidism was found in six cases