Asymptomatic hyperthyroidism in older adults: is it a distinct clinical and laboratory entity?

Hyperthyroidism is the result of increased serum free thyroid hormone levels and is associated with a well recognized set of clinical signs and symptoms. However, older patients who develop hyperthyroidism tend to have fewer hyperadrenergic signs and an increased incidence of weight loss, cardiac arrhythmias and, occasionally, apathetic mood. This article highlights the paucity of clinical signs and symptoms of hyperthyroidism in older people and reviews the potential biochemical changes in thyroid hormone physiology that may account for an altered clinical presentation in older people with hyperthyroidism. First, a brief vignette from our own clinical practice is described to highlight an unusual presentation of hyperthyroidism in an older woman. The subject is then reviewed on the basis of relevant articles identified through a MEDLINE search of the English literature, using the key words 'hyperthyroidism' and 'aging'. The available evidence indicates that the clinical syndrome of asymptomatic hyperthyroidism in older adults appears to be distinct from the more widely recognized syndromes of apathetic hyperthyroidism or thyroid hormone resistance. Age-related changes in thyroid hormone economy and reduced cellular uptake of thyroid hormone as well as changes in thyroid hormone regulation of gene expression may account for reduced manifestations of hyperthyroidism in older adults. Thus, in addition to the well known changes in thyroid gland anatomy and function with aging, there may be an age-related resistance to thyroid hormone action. Asymptomatic hyperthyroidism may well be a syndrome that is currently under-diagnosed.