Thyroid disorders

Evidence of hyperthyroidism has a prevalence rate as high as 2.7%.¹ Hypothyroidism, including subclinical hypothyroidism, has a prevalence rate as high as 20% in the elderly population.¹ The reported prevalence of hypothyroidism is three times higher among women than men.¹ Abnormal thyroid-stimulating hormone (TSH) values are found in as many as 40% of acutely ill elderly patients.² It is important to note that there is a debate regarding clinical significance of elevations of TSH in the elderly population, particularly among the oldest old. Controversy exists about issues as critical as whether having mild thyroid dysfunction may actually have an improved mortality among older persons.

Abnormal TSH does not mean thyroid disease.

CASE 1 Mary Peterson (Part 1)

Mary Peterson is an 84-year-old new patient to your office who presents for a complete evaluation. Initial history is remarkable for mild cognitive impairment, dysthymia, fatigue, and decline in instrumental activities of daily living (IADL) function. Physical examination is remarkable for slowing of deep tendon responses, bradycardia, and slowing of mobility as assessed by the “get up and go” test.

What would be appropriate initial screening laboratory test(s)?

Impact

Thyroid dysfunction, in particular hypothyroidism, may have significant impact on the high rate of mental illness, particularly depression, among elderly persons. Thyroid dysfunction is also significantly related to lipid abnormalities, and lipid levels should be checked in all patients with thyroid underactivity; as well, thyroid activity should be checked in all patients with elevated cholesterol levels.³ Thyroid disorders are more likely to go undiagnosed in patients over the age of 65 than in younger populations.³ Hypothyroidism has been associated with a general slowing of mental and physical function, cold intolerance, weight gain, constipation, effects on blood pressure, and anemia. Although hyperthyroidism is associated with irregular heart rhythms, congestive heart failure, weight loss, and muscular weakness, these symptoms are common findings in numerous geriatric syndromes.⁴

Thyroid dysfunction must be sought when evaluating depression (and other mental illness) in elders.

Risk factors and pathophysiology

With age, the thyroid gland atrophies, fibrosis occurs, and there is accompanied lymphocytic infiltration as well as increasing colloid nodular production. Production of thyroxine (T₄) decreases with age; however, clearance is also reduced, leading to unchanged (T₄) levels. Triiodothyronine (T₃) levels remain unchanged in healthy older subjects.⁵ The body’s decreased use of thyroid hormone is felt to be related to a decline in lean body mass, including the metabolically active muscle, skin, bone, and viscera.

CASE 1 Mary Peterson (Part 2)

Ms. Peterson is screened for thyroid dysfunction with a serum TSH, and this reveals a TSH of 38 IU/mL. This was confirmed by a low T₄.

1. Is this patient a clear candidate for thyroid placement?

2. Is this patient likely to have other identifiable symptoms of hypothyroidism on further review?

Hypothyroidism

The most common etiology of hypothyroidism is previous Hashimoto’s disease (a cell-mediated autoimmune inflammatory process with the presence potentially of four different types of thyroid-directed antibodies), irradiation, surgical removal of the thyroid gland, or idiopathic hypothyroidism. Less common causes include pituitary and hypothalamic disorders leading to TSH deficiencies or iodine-induced hypothyroidism most commonly from medical agents, medications including amiodarone, potassium iodide, lithium, antithyroid drugs, or radio contrast agents.⁶ Populations at high risk of thyroid dysfunction include people with high levels of radiation exposure, the elderly, and people with Down’s syndrome.⁷ People with diabetes are also felt to be at high risk of hypothyroid dysfunction.

See “Mary Peterson, Part 3: Discussion.”

Hyperthyroidism

The prevalence of hyperthyroidism in older adults is 0.5% to 4%.⁸ Hyperthyroidism is most likely due to Graves’ disease with multinodular or uninodular active nodular goiter. Graves’ disease is an auto-immune disorder with antibody formation to the TSH receptor and/or thyroid follicular cells. This antibody has TSH-like activity. Other etiologies include granulomatous or lymphocytic thyroiditis, in which there is leakage of thyroglobulin from the follicles. There are also iatrogenic sources of hyperthyroidism, including that induced by iodine or the use of amiodarone or from the over-ingestion of thyroid repletion agents.⁶