Hypothyroidism in the Elderly: Pathophysiology, Diagnosis and Treatment

Abstract

Some degree of hypothyroidism is common in the elderly. It affects 5–20% of women and 3–8% of men. The occurrence varies with genetics with a high prevalence in Caucasians, and the disease is more common in populations with a high iodine intake. The common causes of hypothyroidism are autoimmune destruction of the thyroid gland and previous thyroid surgery or radioiodine therapy. Various types of medication, including amiodarone, cytokines and lithium, often induce hypothyroidism. Symptoms may be atypical and measurement of serum thyroid-stimulating hormone (TSH) levels should be part of biochemical testing for undiagnosed medical conditions in elderly subjects. The finding of an elevated serum TSH level should be confirmed by repeated testing and supplemented with measurements of serum levels of thyroxine (T₄) and thyroid peroxidase antibodies to verify, quantify and subclassify the abnormality. The recommended and appropriate replacement therapy for hypothyroidism is levothyroxine sodium. The initial replacement dose should be low if heart disease is suspected. Because of the long half-life of levothyroxine sodium small dosage adjustments may be performed by adding or withdrawing a tablet once or twice weekly. Levothyroxine sodium is only partly absorbed after oral ingestion, and food, minerals, drugs and tablet composition influence absorption. Studies performed a few years ago suggested that a combination of levothyroxine sodium and liothyronine may improve clinical results, but recent more comprehensive studies have not supported this hypothesis. Accordingly, liothyronine replacement is not documented to be of benefit. If liothyronine is added to replacement, the liothyronine dose should be kept low, within the physiological range and, preferably be administered twice daily. Thyroid hormone therapy has no beneficial effect above placebo in elderly individuals with normal serum TSH levels and T₄ levels. The major risk of levothyroxine sodium therapy is over-replacement, with anxiety, muscle wasting, osteoporosis and atrial fibrillation as adverse effects. Subclinical hypothyroidism with elevated serum TSH levels but T₄ levels within the laboratory reference range is a mild variant of overt hypothyroidism. Patients with subclinical hypothyroidism should be informed about the disease and offered the possibility of replacement. Only some patients treated for subclinical hypothyroidism will feel better after therapy. In elderly patients on replacement therapy, care should include estimation of serum TSH level once or twice a year, with small dosage adjustments of levothyroxine sodium to keep serum TSH level within the normal range.