Diagnostic algorithm for atrial fibrillation caused by occult hyperthyroidism.

Occult hyperthyroidism, a subclinical thyrotoxic state, is not readily identifiable clinically or through routine thyroid function tests. "Idiopathic" atrial fibrillation may be a manifestation of occult hyperthyroidism in the elderly. A normal response on a TRH stimulation test excludes this diagnosis. A blunted TSH response, coupled with elevation of free thyroid hormones and a high radioactive iodine uptake, will settle the diagnosis. Patients with occult hyperthyroidism frequently have toxic adenomas or nonpalpable nodular goiters, and treatment is best achieved with radioactive iodine ablation.