Autonomously functioning thyroid nodule.

We report 408 cases of autonomously functioning thyroid nodule (AFTN); 85.5% occurred in female patients, for a male-female ratio of 1:6. Eighty-nine patients (21.8%) were hyperthyroid, 76 of them being female, also yielding a male-female ratio of 1:6. There was a linear increase in the incidence of hyperthyroidism with age and with an increase in the size of the nodule, especially for nodules more than 3 cm in diameter. There was a significantly higher incidence of hyperthyroidism for nodules of the same size when they occurred in patients more than 40 years of age. There was a corresponding increase in hyperthyroidism with an increase in the length of time after the initial detection of the nodule; this finding was significantly greater in patients more than 40 years of age. Thus, the age of the patient was found to be a more important determinant in the production of hyperthyroidism associated with an AFTN than either the size of the nodule or the duration of symptoms.