Exam findings associated with a hypo-functioning thyroid may include an enlarged thyroid gland (goiter) or nonpalpable gland, non-pitting edema (myxedema), sinus bradycardia, decrease in body temperature, and delayed relaxation of the deep tendon reflexes. Secondary laboratory abnormalities associated with hypothyroidism include normacytic anemia and elevated lipoproteins. Without specific thyroid testing, a “normal” physical does not rule out thyroid dysfunction.
Hyperthyroidism can also manifest as a depression in elders, known as “apathetic hyperthyroidism.” Patients report decreased cognition, depression, and fatigue, and often experience unexplained weight loss, muscle weakness, or atrial fibrillation. Therefore, elderly patients presenting with depression may have a hyper- or hypo-functioning thyroid.
Case 1 concluded The treating psychiatrist diagnosed the patient with major depression. In addition to treatment with an antidepressant, the patient underwent laboratory testing, including a complete blood count, metabolic panel, and TSH (thyroid stimulating hormone). Test results were normal except for a TSH of 64 mU/L, consistent with hypothyroidism. The patient was referred to her primary care physician to begin thyroid hormone replacement.
Comment Although psychiatric symptoms may be caused by clinically important thyroid dysfunction, thyroid function testing may uncover abnormalities of questionable clinical significance. The prevalence of abnormal thyroid hormone levels in hospitalized psychiatric patients ranges from 3% to 32%.2 High thyroid levels (free T4 index and total T4) are associated with acutely psychotic patients such as those with schizophrenia, affective psychosis, and amphetamine abuses. Most studies show that these changes are transient and often normalize with correction of the psychiatric condition, usually within 10 days. Many researchers believe these findings are consistent with euthyroid sick syndrome (Box 2).3
Depressed patients and those with bipolar disorder often present with altered measures of the hypothalamic-pituitary-thyroid (HPT) axis. These abnormalities include mildly elevated or depressed T3, T4 and TSH levels and are not indicative of true thyroid dysfunction (Table 1). It has been debated whether these patients differ in prognosis from psychiatric patients without such abnormalities, although data in depressed patients suggest equivalent outcomes.4 Furthermore, there is no clear evidence that thyroid supplementation benefits depressed patients with mildly elevated TSH with normal T4 and T3 values.5
The prevalence of thyroid disorders in the general population depends largely on the age, sex, and iodine consumption of the population studied. Women in general face a greater risk of overt thyroid dysfunction than do men, and elders face a greater risk than do the young. High dietary iodine consumption is associated with autoimmune hypothyroidism, especially in the aged. Iodine deficiency facilitates the development of hyperthyroidism secondary to toxic nodular goiter.
Table 1
INTERPRETING TEST RESULTS
| Cause | TSH | Free T4 | Free T3 |
|---|---|---|---|
| Hypothyroidism | Increased | Decreased | Normal or decreased |
| Hypothyroidism | Decreased | Increased | Increased |
| Subclinical hypothyroidism | Increased | Normal | Normal |
| Subclinical hypothyroidism | Decreased | Normal | Normal |
| Euthyroid sick syndrome | Normal or decreased | Normal or decreased | Decreased |
| Hypothalamic pituitary disorder | Decreased | Decreased | Normal or decreased |
| Hypothalamic pituitary disorder | Increased | Increased | Normal or decreased |
A number of other risk factors should also clue the clinician to thyroid dysfunction (Table 2).
Case 2: Subclinical thyroid abnormalities
S.J., 34, has a history of panic disorder that has been well controlled with a selective serotonin reuptake inhibitor (SSRI). He is referred to a primary care physician for an annual physical exam. His blood pressure is elevated as it has been on several occasions over the past year. His physical exam is otherwise normal. Laboratory and ECG test results are normal, except for an elevated TSH at 12 mU/L. Follow-up free T4 and free T3 tests are within normal limits. S.J. agrees to eat less salt to address his hypertension.
Challenge An elevated or decreased TSH with a normal thyroxine level (Table 1) is referred to as a “subclinical” thyroid disorder, which is more common than overt thyroid disorders. Women and elders are at greatest risk for subclinical hypothyroidism. In patients older than 60, the rate can be as high as 17% in women and 15% in men.6 The rate largely depends on the number of patients receiving exogenous thyroid hormone—16% in populations including individuals receiving exogenous thyroid hormone and as low as 0.6-1.1% in populations without such patients.1 Chronic subclinical hypothyroidism or mild thyroid failure is the most common condition found in thyroid function screening.
Table 2
WHEN TO CONSIDER THYROID DYSFUNCTION
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Although patients with subclinical abnormalities appear to be symptom-free, there are clinical implications for these patients. Subclinical hyperthyroidism in the elderly increases the risk for atrial fibrillation and osteoporosis. Postmenopausal women with chronically low TSH measures have lower bone density, especially in cortical bone (e.g., the forearm and hip). Subclinical hypothyroidism is associated with lipid abnormalities and progression to overt hypothyroidism. More recently it has become apparent that this “subclinical” syndrome is not as symptom-free as once assumed, with dry skin, cold intolerance, and easy fatigability more common than in euthyroid patients.7