Physiology and Diseases of the Thyroid Gland in the Elderly: Physiological Changes, Hypothyroidism, and Hyperthyroidism

Clinical and subclinical hypothyroidism, and autoimmune thyroiditis, are more common in older individuals. Nonspecific symptoms often delay diagnosis. Thyroid function tests can be altered by nonthyroidal diseases and medications. Elevated serum TSH and decreased free T4 are diagnostic of primary hypothyroidism. Older patients often need lower L-T4 doses. L-T4 overreplacement should be prevented to lessen risks of atrial dysrhythmias and bone loss. The benefits of normalizing serum TSH in older patients with subclinical hypothyroidism (TSH > 4-5 mU/L with normal free T4) vary considerably. Patients with TSH > 10 mU/L should be treated with low L-T4 doses, as they are more often symptomatic, progress to clinical hypothyroidism, and exhibit increased CV mortality and heart failure (HF) risk. Hyperthyroidism in the elderly increases CV morbidity and mortality. The most common causes are overtreatment with L-T4 and toxic multinodular goiter (MNG). Clinical presentation can be atypical, with more frequent and severe cognitive and CV manifestations and fewer symptoms of sympathetic activation. Diagnosis requires low TSH and elevated free T4 or total T3, and confounding effects of drugs and acute or chronic illnesses should be considered. Treatment should be individualized. Radioiodine following thyroid hormone normalization with methimazole and symptomatic administration of beta blockers is the preferred therapy. Surgery is rarely used as definitive treatment. Subclinical hyperthyroidism, with isolated low TSH, is more common in the elderly and increases atrial fibrillation risk. Treatment is indicated when TSH is < 0.4 mU/L.