Differences in thyroid function between bipolar manic and mixed states

High rates of thyroid axis abnormalities have been reported in most studies of patients with rapid-cycling bipolar disorder. Mixed states share similarities with rapid-cycling, including close temporal occurrence of manic and depressive symptoms, predominance in women, poor outcome, and less robust response to lithium compared with pure mania; however, thyroid axis abnormalities have not been well studied in mixed mania.

To test the hypothesis that mixed states are associated with a higher prevalence of hypothyroidism than pure mania, immunoreactive triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH) concentrations were determined from serum obtained at the time of admission in 37 consecutive patients with DSM-III-R bipolar disorder, manic or mixed.

The mean TSH concentration was significantly higher, and the mean T4 concentration was significantly lower in patients with mixed mania compared with pure mania. There were no significant differences in T3 concentration or in previous lithium exposure.

These findings suggest thyroid axis dysfunction is more common in bipolar mixed than in bipolar manic patients.