Subclinical Hyperthyroidism in the Elderly: Small Numbers, Big Consequences

Dear Editor,

Subclinical hyperthyroidism (SCHyper), defined by suppressed serum thyroid-stimulating hormone (TSH) with normal free thyroxine and triiodothyronine, represents a frequently underrecognized condition that disproportionately burdens the elderly population. With a prevalence reaching up to 15.4% in individuals aged 75 years and above, its clinical footprint in geriatric medicine is substantial yet underappreciated.¹

The diagnostic challenge in older adults is compounded by the condition’s insidious nature. Classical hyperthyroid symptoms - palpitations, tremor, heat intolerance, and anxiety - are frequently absent, misattributed to comorbidities, or masked by age-related physiological changes. Consequently, diagnosis relies on biochemical vigilance rather than symptom recognition. Crucially, a single suppressed TSH is insufficient for diagnosis; confirmation requires repeat testing after three to six months, with earlier reassessment - within two to four weeks - warranted in those with atrial fibrillation or established cardiac disease.² Before confirming the diagnosis, common causes of transient TSH suppression must be excluded - including non-thyroidal illness, medications such as dopamine, glucocorticoids, amiodarone, or immune checkpoint inhibitors, and destructive thyroiditis. Unlike true SCHyper, these conditions typically show free T4 and T3 in the lower reference range, with TSH normalizing once the underlying cause resolves.^2,3

The cardiovascular consequences of untreated SCHyper in older adults deserve particular emphasis. A landmark cohort study demonstrated a threefold increased risk of atrial fibrillation in individuals with TSH below 0.1 mIU/L, with risk rising proportionally with the degree of TSH suppression.⁴ Beyond arrhythmia, pooled analyses from prospective cohorts confirm elevated risks of heart failure and excess coronary and all-cause mortality, with the greatest excess concentrated in adults over 65 years.⁵ These are not trivial endpoints in a population already at elevated baseline cardiovascular risk.

Skeletal consequences are similarly consequential. Postmenopausal women with endogenous SCHyper face increased rates of bone loss and fracture, with those carrying TSH below 0.1 mIU/L demonstrating the highest fracture burden. Prospective data suggest that successful normalization of TSH - through antithyroid drugs or radioactive iodine - stabilizes or partially reverses bone loss in this group.⁶

Beyond cardiovascular and skeletal consequences, SCHyper carries significant neuropsychiatric implications in older adults. Anxiety, irritability, emotional lability, and sleep disturbance may occur even without overt thyrotoxic symptoms and are frequently misattributed to primary psychiatric conditions or aging. Longitudinal data further link suppressed TSH with increased dementia and Alzheimer’s risk, particularly in women. While causality remains unresolved, neuropsychiatric manifestations should be actively elicited during clinical assessment of elderly patients with SCHyper.^7,8

Management must be individualized. Current guidelines from the American thyroid association and the European thyroid association recommend treatment for grade 2 SCHyper (TSH < 0.1 mIU/L) in adults aged 65 years and above, and for grade 1 SCHyper (TSH 0.1–0.4 mIU/L) when cardiovascular disease, osteoporosis, or hyperthyroid symptoms coexist.² For frail patients and those with toxic multinodular goiter - the predominant endogenous etiology in iodine-deficient regions, including parts of India - radioactive iodine is generally the preferred definitive modality, avoiding the polypharmacy burden and monitoring complexity associated with long-term antithyroid drug use.⁷

We advocate for systematic opportunistic case-finding through TSH measurement in high-risk elderly individuals - particularly women over 60, those with new-onset atrial fibrillation, unexplained osteoporosis, or receiving levothyroxine or amiodarone - even in the absence of classic symptoms. This approach is pragmatic, low-cost, and actionable within resource-constrained settings. Finally, we wish to emphasize the need for heightened awareness of SCHyper among primary care physicians and geriatric practitioners, who are often the first point of contact for elderly patients. Given the condition’s atypical presentation, its overlap with age-related comorbidities, and its multisystem consequences spanning cardiovascular, skeletal, and neuropsychiatric domains, clinical suspicion must be actively cultivated rather than awaited. Routine biochemical screening in high-risk elderly individuals, prompt specialist referral when indicated, and individualized risk-stratified management should be integral to geriatric and primary care practice.