Influence of Age on Optimal Daily Levothyroxine Dosage in Patients With Primary Hypothyroidism Grouped According to Etiology

Abstract

Optimal daily levothyroxine (LT4) dosage is reported to be significantly smaller in the elderly with primary hypothyroidism when compared with their younger counterparts. However, this finding has not been studied in different etiologic groups. This study assessed the influence of age on optimal daily LT. dosage in 337 patients with primary hypothyroidism grouped according to etiology. Daily LT. dosage declined with increasing age in 99 patients with Hashimoto's thyroiditis, in 73 patients with idiopathic variety, and in 47 patients with hypothyroidism due to radical neck surgery and/or neck radiation for non-thyroidal malignancies. In contrast, daily LT. dosage rose with age in 85 patients who had radioiodine (131I) therapy and/or subtotal thyroidectomy for hyperthyroidism. Finally, daily LT. dosage was not significantly altered in 22 patients with subclinical hypothyroidism or in 11 patients with drug-induced hypothyroidism. Optimal daily LT4 dosage does not decline universally in all elderly with primary hypothyroidism: it appears to depend also on the etiology of the disorder.