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Incidence and Determinants of Spontaneous Normalization of Subclinical Hypothyroidism in Older Adults.
van der Spoel, E, van Vliet, NA, Poortvliet, RKE, Du Puy, RS, den Elzen, WPJ, Quinn, TJ, Stott, DJ, Sattar, N, Kearney, PM, Blum, MR, et al
The Journal of clinical endocrinology and metabolism. 2024;109(3):e1167-e1174
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With increasing age, circulating levels of thyroid stimulating hormone (TSH) generally rise, accompanied by a higher prevalence of subclinical hypothyroidism. Subclinical hypothyroidism is defined as an elevated TSH level while the serum free T4 (fT4) concentration is within the normal range. The aim of this study was to investigate the incidence of spontaneous normalisation of TSH levels and identify determinants of normalisation in a large group of adults aged 65 years and older with (persistent) subclinical hypothyroidism. This study was a longitudinal study that pooled data from 2 randomised, double-blind, placebo-controlled parallel-group clinical trials. Results showed that 60.8% of the older adults with biochemical subclinical hypothyroidism based on at least 1 elevated TSH measurement, TSH levels had returned to the normal range without intervention after a median follow-up of 1 year. Subsequently, TSH levels had still normalised after 1 year in 39.9% of older adults with persistent subclinical hypothyroidism. Younger age, female sex, lower initial TSH level, higher normal initial fT4 level, the absence of thyroid peroxidase antibodies, and a second measurement in summer were independent determinants for TSH normalisation. Authors concluded that since TSH levels spontaneously normalised in a large proportion of older adults with subclinical hypothyroidism, a third measurement is recommended before considering treatment.
Abstract
CONTEXT With age, the prevalence of subclinical hypothyroidism rises. However, incidence and determinants of spontaneous normalization remain largely unknown. OBJECTIVE To investigate incidence and determinants of spontaneous normalization of TSH levels in older adults with subclinical hypothyroidism. DESIGN Pooled data were used from the (1) pretrial population and (2) in-trial placebo group from 2 randomized, double-blind, placebo-controlled trials (Thyroid Hormone Replacement for Untreated Older Adults With Subclinical Hypothyroidism Trial and Institute for Evidence-Based Medicine in Old Age thyroid 80-plus thyroid trial). SETTING Community-dwelling 65+ adults with subclinical hypothyroidism from the Netherlands, Switzerland, Ireland, and the United Kingdom. PARTICIPANTS The pretrial population (N = 2335) consisted of older adults with biochemical subclinical hypothyroidism, defined as ≥1 elevated TSH measurement (≥4.60 mIU/L) and a free T4 within the laboratory-specific reference range. Individuals with persistent subclinical hypothyroidism, defined as ≥2 elevated TSH measurements ≥3 months apart, were randomized to levothyroxine/placebo, of which the in-trial placebo group (N = 361) was included. MAIN OUTCOME MEASURES Incidence of spontaneous normalization of TSH levels and associations between participant characteristics and normalization. RESULTS In the pretrial phase, TSH levels normalized in 60.8% of participants in a median follow-up of 1 year. In the in-trial phase, levels normalized in 39.9% of participants after 1 year of follow-up. Younger age, female sex, lower initial TSH level, higher initial free T4 level, absence of thyroid peroxidase antibodies, and a follow-up measurement in summer were independent determinants for normalization. CONCLUSION Because TSH levels spontaneously normalized in a large proportion of older adults with subclinical hypothyroidism (also after confirmation by repeat measurement), a third measurement may be recommended before considering treatment. TRIAL REGISTRATION ClinicalTrials.gov, NCT01660126 and Netherlands Trial Register, NTR3851.