Clinical manifestations of major depressive disorder (MDD) such as suicide attempts and psychiatric symptoms may be associated with severe subclinical hypothyroidism (SCH), according to study results published in the Journal of Affective Disorders.

SCH and overt hypothyroidism are found to be more prevalent in patients with MDD than in the general population. The coexistence of SCH and depression suggests that the 2 conditions may share some clinical characteristics and associations. The objective of this study was to investigate the prevalence and clinical correlates of severe SCH in patients with MDD in their first episode.

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In this study, researchers recruited 1706 patients with MDD from a psychiatric clinic at the First Affiliated Hospital of Shanxi Medical University in China. Depression symptoms were evaluated using the 17-item Hamilton Depression Rating Scale (HAMD), anxiety symptoms were evaluated using the Hamilton Anxiety Rating Scale (HAMA), and psychiatric symptoms were evaluated using the positive subscale of the Positive and Negative Syndrome Scale (PANSS). 

Blood samples were collected from all patients, from which serum thyroid-stimulating hormone (TSH) were examined with a chemiluminescence immunoassay. SCH was defined as TSH>4.2 mIU/L with fT4 levels within the reference ranges. Based on the serum TSH level, SCH was further divided into mild (TSH<10 mIU/L) and severe (TSH≥ 0 mIU/L).

Results revealed that the prevalence of SCH in the total sample was 60.7% (n=1036).  More patients with severe SCH had suicide attempts, severe anxiety, and psychiatric symptoms (all P <.001) compared with those without severe SCH. Patients with severe SCH also had higher fT4 levels (P <.05), blood pressure (P <.001), HAMD scores (P <.001), HAMA scores (P <.001), and PANSS positive subscores (P <.001) compared with those without severe SCH. 

Binary logistic regression showed that patients with suicide attempts and psychiatric symptoms were more likely (4.53 times and 5.93 times, respectively) to have severe SCH, compared with those without these clinical correlates (both P <.001). Stepwise multiple linear regression revealed that HAMD score (P <.001), body mass index (P <.001), course of illness (P <.001), CGI score (P =.001), HAMA score (P <.001), and PANSS positive subscore (P >.001) were all associated with decreased TSH levels.

This study had several limitations that reduce generalizability to other settings. Patients were recruited from only 1 hospital, data regarding TSH level before the onset of depression were not available, and the study included a higher number of women than men. In addition, entire thyroid hormone profiles were not examined, and all the instruments were in Chinese only. Suicide attempts were assessed using a screening question instead of a validated questionnaire, and the study did not use a healthy control group. Last, all medication information was obtained through patient and relative interviews rather than from medical records.

The study researchers concluded that severe SCH is closely related to clinical manifestations of MDD and that patients with MDD should undergo regular screening of serum TSH levels to reduce the risk of suicide and psychiatric symptoms. They further recommend treatment of both SCH and depression to prevent suicide and major depression.

Reference

Lang X, Hou X, Shangguan F, Zhang XY. Prevalence and clinical correlates of subclinical hypothyroidism in first-episode drug-naive patients with major depressive disorder in a large sample of Chinese [published online November 3, 2019]. J Affect Disord. doi: 10.1016/j.jad.2019.11.004