Section 9: Metabolic Diseases

9.2. Thyroid Disease

9.2.a. Hyperthyroidism

9.2.b. Hypothyroidism

9.2a. Hyperthyroidism

Hyperthyroidism is the clinical expression of a group of disorders that produces elevated levels of free thyroxineand/or triiodothyronine (Gorroll, May, and Mulley, 1987). Disorders include toxic goiter (Grave's disease), toxic multinodular goiter, and toxic uninodular goiter. Although the prevalence of hyperthyroidism is not known precisely, community-based studies report prevalence rates of 1.9 percent in women and 0.16 percent in men (Gorroll, May, and Mulley, 1995). Approximately 15 percent of recognized cases occur in people older than 60 (Gorroll et al., 1995).

Clinical symptoms of hyperthyroidism include nervousness, tremor, muscle weakness, increased appetite, weight loss, and heat intolerance. In the elderly individual, symptoms may be atypical, with the patient presenting with apathy, weight loss, and cardiovascular dysfunction (unexplained atrial fibrillation). A number of therapeutic agents are available for the treatment of hyperthyroidism.

9.2b. Hypothyroidism

Of the thyroid disorders, hypothyroidism is the more common. The condition is most often caused by some disorder of the thyroid gland that causes decreased thyroid hormone production and secretion (Barnes, 1990). Iodine deficiency is the most common cause worldwide of hypothyroidism. In regions where iodine intake is adequate, the most common causes are chronic autoimmune thyroiditis (Barnes, 1990).

Clinically, the patient with hypothyroidism presents with the following symptoms: fatigue, lethargy, sleepiness, dry skin, cognitive impairment, intolerance to cold, and weight gain. Fatigue, sleepiness, and cognitive impairment are the symptoms with the greatest relevance for driving. Once the diagnosis is established, treatment consists of thyroid hormone replacement therapy.

As with hyperthyroidism, hypothyroidism affects more women than men. The prevalence of hypothyroidism increases with age. According to Goroll et al. (1987), as much as five percent of the elderly population show evidence of hypothyroidism. Subclinical hypothyroidism, on the other hand, is estimated to affect between four percent and 14 percent of people older than 60, with more females than males affected.