The Effect of Thyroid Hormone Therapy on Muscle Mass and Function in Older Adults With Subclinical Hypothyroidism - a Substudy of TRUST and IEMO Trials

Background

Subclinical hypothyroidism (SCH) is common among the elderly population, with an estimated prevalence of 6-15%. It has been associated with multiple adverse outcomes such as cardiovascular diseases and neuropsychological disturbance. Muscular function impairment has also been associated with SCH. However, the association between subclinical hypothyroidism and physical performance in older adults remains unclear and randomized controlled trials are lacking.

Physical performance is an important prognostic indicator for older adults. Prospective studies showed that it is related to hospitalization, institutionalization, cardiovascular disease, disability and mortality. Gait speed is one of the most widely used measures of physical performance in clinical and research settings, with a solid prognostic value.

Aside from overall physical performance, two other dimensions of muscular function can be assessed: muscle function, usually assessed by handgrip strength (predictive validity for decline in cognition, mobility, functional status and mortality for older people), and muscle mass, usually assessed by dual-energy X-absorptiometry). Those three dimension together form the definition of sarcopenia, a relatively new concept which has been gaining visibility in the last years because of its high prevalence and clinical relevance.

Both subclinical hypothyroidism and muscle function impairment are highly prevalent among the older population, and the latter bears a heavy personal, social and economic burden. Therefore, evaluating the potential benefit of levothyroxine therapy on muscle function in this population holds the potential to prevent adverse health-related outcomes and maintain the patients' autonomy and quality of life.