In older adults, mildly elevated TSH levels normalised in about 50% of cases during one to two years of observation. 

Subclinical hypothyroidism – above-normal level of thyroid-stimulating hormone (TSH) but normal free thyroxine (T4) – becomes more common with age. To examine how often subclinical hypothyroidism normalises spontaneously in untreated older adults, European researchers studied two cohorts of older patients (age, 65 years or older). The upper limit of normal for TSH was 4.6 mIU/L.

Findings were as follows:

• one cohort included 2335 patients with one instance of subclinical hypothyroidism (median TSH, 5.4mIU/L). On repeat testing about one year later, TSH had normalised spontaneously in 61% of patients
• a second cohort included 361 patients with two instances of subclinical hypothyroidism separated by about one year (median TSH, 5.75mIU/L). On a third round of testing one year later, subclinical hypothyroidism had normalised in 40% of patients
• normalisation was more likely in women, in people who tested negative for antithyroid peroxidase antibodies and when baseline TSH was only mildly elevated. For example, when baseline TSH was 5mIU/L, it normalised in about 75% of men and women. But when it was 10, it normalised in only 20% of women and 7% of men.

Comment: Diagnosis of subclinical hypothyroidism depends on somewhat arbitrary upper limits of normal for TSH; some experts believe that cut-offs should be higher than 4 or 5 mIU/L in older adults. In any case, these patients generally should be followed without treatment, and this study’s findings can be shared with patients regarding the probability that TSH will normalise. Additionally, other studies have shown that the probability of eventual progression to overt hypothyroidism is about 50% when TSH is closer to 10 mIU/L and antithyroid peroxidase antibodies are present.

Allan S. Brett, MD, Clinical Professor of Medicine, University of Colorado School of Medicine, Aurora, USA.

van der Spoel, E et al. Incidence and determinants of spontaneous normalization of subclinical hypothyroidism in older adults. J Clin Endocrinol Metab 2024; 109: e1167-e1174.

This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine.