Diagnosis and Management of Hyperthyroidism in Older Adults
Older patients with hyperthyroidism present with atypical symptoms such as difficulty concentrating. This is in contrast to younger patients, who present with classic symptoms such as heat intolerance, tremor, and tachycardia. Hyperthyroidism in older adults is most often caused by toxic multinodular goiter and Graves’ disease. Thyroid hormones and thyroid-stimulating hormone assays can establish the diagnosis quickly. Antithyroid medication can be used in medically unstable older hyperthyroid patients to quickly suppress the hormones. When the patient is stable, definitive therapies such as radioactive iodine or surgery should be considered. Radioactive iodine therapy is well tolerated and effective. Surgery is indicated in patients who fail to respond to radioactive iodine therapy and patients with multinodular goiter.
Key words: thyrotoxicosis, older adults, hyperthyroidism, Graves’ disease, T3 toxicosis.
Introduction
Hyperthyroidism is common among older adults.1 Hyperthyroidism is a highly treatable condition but can cause life-threatening complications in older individuals if not treated in a timely manner.2,3 Individuals over the age of 60 constitute 10-15% of those affected by hyperthyroidism.4,5 The prevalence of hyperthyroidism ranges from 0.5-6%.6-14 The thyroid gland releases two thyroid hormones, thyroxine (T4) and triiodothyronine (T3), in a molar ratio of 14:1. All of the T4 in the body is made within the thyroid gland, whereas 80% of T3 is derived in the peripheral tissues. The synthesis and release of thyroid hormone are controlled by pituitary-derived thyroid-stimulating hormone (TSH), under the influence of thyrotropin-releasing hormone from the hypothalamus.
Clinical presentation of thyroid hyperfunction differs among older adults as compared to a younger cohort (Figure 1).15,16 There are many causes of thyrotoxicosis (excessive concentrations of thyroid hormones) in older adults (Table 1). The most common cause of hyperthyroidism in older individuals is toxic multinodular goiter17-24 followed by Graves’ disease.2,3 Subacute thyroiditis may cause transient hyperthyroidism, but it is rarely a problem in older adults, and the incidence is very low in this patient population. Iodine excess or drugs that contain iodine may also lead to thyroid dysfunction among older adults.25 Increased iodine uptake from drugs such as mucolytics or contrast media may cause iodine-induced hyperthyroidism (Jod-Basedow disease). Polypharmacy is common in older adults, and Table 2 lists drugs that can cause thyrotoxicosis. Amiodarone, an antiarrythmic commonly used among older adults for atrial fibrillation, can cause hyperthyroidism in 5% of treated patients or hypothyroidism in 7% of treated patients. Amiodarone delivers 7.4 mg of free iodine load per 200 mg tablet.26
Clinical Features
Among younger adults, the classic symptoms of thyroid dysfunction (tachycardia, palpitations, heat intolerance, tremors, and sweating) are usually present and make the diagnosis easier. Among older adults, the diagnosis is more often overlooked or misdiagnosed as many patients are asymptomatic or present with atypical symptoms.9,27 Recognition of hyperthyroidism in this patient population depends upon a high index of suspicion on the part of the clinician and willingness to seek confirmation by appropriate laboratory testing.
Hyperthyroidism may be overlooked as some symptoms such as difficulty in concentrating or weight loss may be attributed to normal aging.28 At times the symptoms