Atypical Depression: Thyroid Link Still Alive
Antithyroid Antibodies May Signal Difficult-to-Treat Depression
March 15, 2004 -- A specific form of depression may be linked to thyroid function, new research shows.
The finding rekindles the long-smoldering debate about the role of thyroid function in depression. It's clear that thyroid problems can cause depression. Indeed, doctors regularly screen depressed patients for thyroid trouble. But researchers are still arguing over whether subclinical thyroid problems -- those that don't cause any other obvious symptoms -- play a role in depression.
Maybe only certain kinds of depression are linked to thyroid dysfunction, wondered Konstantinos N. Fountoulakis, MD, PhD, of the University of Thessalonica, Greece, and colleagues. To test this idea, they studied 30 patients with major depression and compared them with 60 normal volunteers.
Sure enough, there was no overall link between depression and thyroid dysfunction. Thyroid function tests were normal in all the subjects, but a subset of the depressed patients -- those with atypical depression -- was much more likely to show laboratory evidence of autoimmune thyroid dysfunction. They were more likely than other depressed patients to have significantly higher levels of antithyroid antibodies. The study results appear in the current issue of BMC Psychiatry.
"We don't know whether depression led to this autoimmune response or whether the autoimmunity produced depression," Fountoulakis tells WebMD. "What is the cause and what is the effect is still unclear."
It's a chicken-or-egg situation, agrees Victor J. Pop, MD, PhD, professor of clinical health psychology at the University of Tilburg, Netherlands. Pop says it's clear that depression and subtle thyroid problems are linked -- but which comes first is still not known.
It is known that depression can cause the controls for hormones to be altered, even though there may not be overt clinical disease, Pop tells WebMD. "If you take 1,000 normal women, and check their blood with highly sophisticated tests, you will find 2% to 4% have subclinical thyroid dysfunction. But if you take 1,000 depressed people, four times as many will have these subtle thyroid dysfunctions."
Pop has found evidence linking subtle thyroid dysfunction to postpartum depression. Fountoulakis, on the other hand, focuses on atypical depression.
A Different Kind of Depression
Fountoulakis hopes a better understanding of antithyroid antibodies leads to better diagnosis and treatment of atypical depression. That's because it's much harder to treat than other forms of depression.
People with atypical depression often feel "leaden paralysis" -- the feeling that their limbs are so heavy they can barely find the energy to move them. Instead of losing weight, they gain weight. Instead of losing sleep, they sleep too much. And instead of feeling no emotion, they tend to feel anxious. Atypical depression is also linked to other psychiatric problems such as borderline personality disorder.
"There is an assumption that you can reverse this depression by treating thyroid function. Or perhaps we can routinely screen depressed patients for these antibodies so we know which patients will be less likely to respond to treatment. But it is too early to say that," Fountoulakis says. "The problem is that endocrinologists don't know how to treat these conditions of medium-to-low levels of antithyroid antibody. Because this is not an overt thyroid disease, this is nonspecific abnormality. It may well be produced by the severity of the depressive illness itself."
SOURCES: Fountoulakis, K.N. BMC Psychiatry, 2004; vol 4. Konstantinos N. Fountoulakis, MD, PhD, University of Thessalonica, Greece. Victor J. Pop, MD, PhD, professor, clinical health psychology, University of Tilburg, Netherlands.