Autoimmune Thyroid Disease Linked to Depression

Laurie Barclay, MD

March 15, 2004

March 15, 2004 — Autoimmune thyroid disease may be linked to depression, according to the results of a small study published in the March 15 issue of BMC Psychiatry.

"Unipolar depression might be characterized by a 'low-thyroid function syndrome,' " write Konstantinos N. Fountoulakis from Aristotle University of Thessaloniki in Greece, and colleagues. "There is a lot of evidence suggesting the presence of an underlying autoimmune disorder in unipolar depression, with the possible involvement of the thyroid gland, however, studies are inconclusive and fail to differentiate between different clinical subtypes of depression."

This study enrolled 30 patients (10 men and 20 women) with major depressive disorder, aged 21 to 60 years, and 60 healthy controls. Using the schedules for Clinical Assessment in Neuropsychiatry and a structured interview, two psychiatric examiners determined clinical diagnosis. Ten patients had atypical features by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria; 12 had melancholic features; and eight were undifferentiated. All subjects were physically healthy and were medication-free for at least two weeks.

Thyroid function markers FT3, FT4, and TSH were normal in all subjects. Compared with control patients, all depressive subtypes had significantly higher thyroid binding inhibitory immunoglobulins, and atypical patients had significantly higher thyroid microsomal antibodies. None of the thyroid indices correlated significantly with the Hamilton Depression Rating Scale, the Hamilton Anxiety Scale, or the Global Assessment of Functioning Scale.

Discriminant function analysis identified different algorithms based on thyroid indices that could predict diagnosis of depression with 80% sensitivity, moderately differentiate between diagnostic groups, and predict good response to treatment at two years with a success rate of 89.47%. Higher immunoglobulin levels were associated with reduced responsiveness to treatment, suggesting the need for specific therapeutic intervention.

"Although thyroid dysfunction is not common in depression, there is evidence suggesting the presence of an underlying autoimmune process affecting the thyroid gland in depressive patients," the authors write. "The finding that depression often co-exists with autoimmune subclinical thyroiditis suggests that depression may cause alterations in the immune system, or that in fact it is an autoimmune disorder itself."

Because of study limitations, notably small sample size, the authors recommend additional research to confirm these findings and to explore any causal relationships between thyroid abnormalities and depression.

The authors report no potential financial conflicts of interest.

BMC Psychiatry. 2004;4(6) [Published online March 15, 2004.]

Reviewed by Gary D. Vogin, MD


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