[Effects of thyroid hormone replacement therapy on nocturnal apnea in elderly patients with hypothyroidism]

Because the incidence of sleep apnea is known to increase in both hypothyroidism and with age, elderly hypothyroid patients may experience more sleep apnea than younger hypothyroidism patients. However, the features of nocturnal disturbed breathing in elderly hypothyroid patients have not been fully elucidated. Concise polysomnographic studies including respiratory movement and oxyhemoglobin saturation (SaO2) were done on 18 elderly subjects with hypothyroidism (73.6 +/- 5.9 years old) before and after thyroid hormone replacement therapy. Fourteen of the patients exhibited a significant incidence of nocturnal apnea. Lower incidence of nocturnal apnea and higher nocturnal nadir SaO2 were observed in the patients 3 to 6 months after thyroxine therapy. Although the levels of thyroid hormones returned to normal in the patients, 9 patients had more than 5 bouts of nocturnal apnea per hour after the hormone replacement therapy. Further, no relationship was found between the level of thyroid hormones and the frequency of nocturnal apnea. These results suggest that levels of thyroid hormones are not indicators of the potential severity of nocturnal apnea in elderly hypothyroid patients, and that sleep studies may be necessary to assess the efficacy of thyroid hormone replacement therapy in the treatment of nocturnal apnea.