We aimed to evaluate the risk factors for the development of definitive thyroid failure, to analyze the natural course of subclinical hypothyroidism and to quantify the incidence rate of overt hypothyroidism in elderly patients.
Two hundred and fourteen patients (186 women and 28 men) over age 60 years with subclinical hypothyroidism and no previous history of thyroid disease were prospectively studied. Subjects were followed up for 672 months (mean, 31.7 months) with repeated determinations of TSH and free T4. Fifty-eight patients (27.10%) developed overt hypothyroidism, and 81 (37.85%) showed normalization of their TSH values. The incidence rate of overt hypothyroidism was 9.91 cases per 100 patient-years in the whole population, and 1.76, 19.67, and 73.47 cases per 100 patient-years in subjects with initial TSH values between 6.08.9, 9.013.9, and 14.018.9 mU/l, respectively.
KaplanMeier analysis showed that the development of definitive thyroid hypofunction was significantly related to the presence of symptoms of hypothyroidism, goitre, positive thyroid antibodies (P<0.05), and mainly low normal free T4 (P<0.01) and high TSH (P<0.001) concentrations at baseline. A stepwise multivariate Cox regression analysis showed that the only significant factor for progression to overt hypothyroidism was serum TSH concentration (P<0.001).
In conclusion, TSH concentration is the most powerful predictor for the outcome of spontaneous subclinical hypothyroidism in older. Subjects with mildly elevated TSH have a low incidence rate of overt hypothyroidism. We recommend follow-up with clinical and biochemical monitoring in these patients.
03 - 07 May 2008
European Society of Endocrinology