Many clinical features of hypothyroidism are commonly found in the elderly, despite negligible changes in plasma thyroid hormone levels. These symptoms may reflect the decreased intracellular uptake of T 3 and alterations in gene activation/deactivation that are observed with aging.
On the other hand, numerous studies have shown a 3–4% incidence of unsuspected (subclinical) hypothyroidism in the elderly. Primary thyroid failure, usually secondary to chronic autoimmune thyroiditis, has been estimated to occur in 4.4% of the population over the age of 60 years. The prevalence of antithyroglobulin and antithyroperoxidase antibodies increases with age up to 70, then declines so that prevalence at age 4100 years equals that found in controls o 50 years. In one large study, 80% of elderly patients with high antithyroperoxidase antibody titers developed clinical hypothyroidism during a 4 year follow-up period. In contrast, elevated anti-thyroglobulin antibody titers do not appear to predict increased risk for hypothyroidism.
Hyperthyroidism is more difficult to diagnose in the elderly due to lack of classical clinical signs. Symptoms of hyperthyroidism, especially those secondary to increased adrenergic activity, are frequently blunted in older individuals. The reduced signs of adrenergic hyperactivity in elderly hyperthy-roid patients may be the result of age-related skins problems desen- sitization of b-adrenergic receptors. The heart rate response is reduced in elderly subjects regardless of thyroid status. Low serum TSH is more common in the older patient, most often accomplished by a normal serum T 4 concentration. In one large study, 6 out of 50 elderly patients with low TSH became hyper- thyroid during 4 years of follow-up.
Some of the effects of hyperthyroidism may be totally different in elderly individuals. Weight loss secondary to hyperthyroid status occurs in both young and older individuals. However, the etiologic path-way may be different. As many as 36% of elderly patients with hyperthyroidism experience anorexia. Using pair fed rats, weight loss in hyperthyroid older rats has been linked directly to decreased food intake in the aged rats compared with their younger counterparts.
A high index of suspicion, appropriate laboratory testing, and careful slow replacement of thyroid hormone when required will greatly facilitate the care of the elderly patient with thyroid disease.
