Subject:
THYROID FUNCTION

Short Description:
Thyroid Function in Psychiatric Illness

Background:

True thyroid dysfunction can present with symptoms as wide-ranging as depression, mania, psychosis, or poor cognition. Thus, we psychiatrists commonly order thyroid function tests for our psychiatric patients, as well as for medical patients with psychiatric symptoms. A recent review, however, notes that lab abnormalities suggesting thyroid dysfunction may not actually signify true thyroid disease. In fact, a wide spectrum of medical illnesses, psychiatric conditions, and medications can all affect thyroid function. Abnormal thyroid function in a depressed patient, for example, may simply reflect the impact of depressive illness upon thyroid function rather than vice versa (Dickerman AL and Barnhill JW, Am J Psychiatry 2012;169(2):127–133).

According to the literature review, the term “non-thyroidal illness” is used to describe abnormal thyroid function secondary to medical or psychiatric conditions. It’s quite common, occurring in 7% to 33% of patients hospitalized for psychiatric disorders. The specific thyroid lab findings among psychiatric patients can vary substantially. The most common finding is hyperthyroxinemia (elevated total and free T4) among patients with mood disorders, which may be due to redistribution of T4 out of tissues or due to hypersecretion of TSH by the hypothalamus during acute mood episodes. Other alterations can also be seen. Stimulants can increase TSH and total T4 levels while opioids can increase total T4 and T3 levels. Lithium can cause true hypothyroidism, while carbamazepine increases metabolism of thyroid hormones in the liver. Thus, patients on carbamazepine who take thyroid supplementation may require higher replacement doses.

The pathophysiology of non-thyroidal illness is not well understood, but it’s clear that abnormal thyroid function tests do very little to guide treatment decisions in psychiatric or acutely ill medical patients. In fact, thyroid function typically normalizes after treatment of the underlying condition. As a result, the authors suggest that psychiatric patients should only be screened for thyroid dysfunction if there’s a clinical reason to suggest it, such as signs or symptoms of actual thyroid disease (eg, goiter; hypothermia; unexplained tachycardia; muscle weakness) or relevant risk factors (eg, autoimmune disorder, lithium history, family history of thyroid disease).

TCPR's Take:
Routine testing of thyroid function among psychiatric and medical patients without signs or risk factors for thyroid disease often yields abnormal results in the absence of actual thyroid dysfunction, and treatment of the abnormal result is generally unnecessary. Sound clinical judgment should be used when ordering and interpreting thyroid function testing.