Thyroid dysfunction is common among major depressive disorder (MDD) patients, but its relationship with the psychotic depression (PD) subtype has not been well studied, wrote Pu Peng, of The Second Xiangya Hospital of Central South University, Changsha, Hunan, China, and colleagues.
Given the significant negative consequences of PD in MDD, including comorbid psychosis, suicidal attempts, and worse prognosis, more ways to identify PD risk factors in MDD are needed, they said. Previous research suggests a role for thyroid hormones in the pathophysiology of PD, but data on specific associations are limited, they noted.
In a study published in Psychiatry Research, the authors recruited 1,718 adults aged 18-60 years with MDD who were treated at a single center. The median age was 34 years, 66% were female, and 10% were identified with PD.
Clinical symptoms were identified using the positive subscale of the Positive and Negative Symptom Scale (PANSS-P), Hamilton Anxiety Rating Scale (HAMA), and Hamilton Depression Rating Scale (HAMD). The median PANSS-P score was 7. The researchers measured serum levels of thyroid stimulating hormone (TSH), anti-thyroglobulin (TgAb), and thyroid peroxidases antibody (TPOAb). Subclinical hyperthyroidism (SCH) was defined as TSH levels greater than 8.0 uIU/L and FT4 within normal values.
Overall, the prevalence of SCH, abnormal TgAb, TPOAb, FT3, and FT4 were 13%, 17%, 25%, <0.1%, and 0.3%, respectively. Serum TSH levels, TgAb levels, and TPOAb levels were significantly higher in PD patients than in non-PD patients. No differences appeared in FT3 and FT4 levels between the two groups.
In a multivariate analysis, subclinical hypothyroidism was associated with a ninefold increased risk of PD (odds ratio, 9.32) as were abnormal TPOAb (OR, 1.89) and abnormal TgAb (OR, 2.09).
The findings were limited by several factors including the cross-sectional design, and the inclusion of participants from only a single center in China, which may limit generalizability, the researchers noted.
In addition, “It should be noted that the association between thyroid hormones and PD was small to moderate and the underlying mechanism remained unexplored,” they said. Other limitations include the use of only 17 of the 20 HAMD items and the lack of data on the relationship between anxiety and depressive features and thyroid dysfunction, they wrote.
More research is needed to confirm the findings in other populations, however; the results suggest that regular thyroid function tests may help with early detection of PD in MDD patients, they concluded.
The study was funded by the CAS Pioneer Hundred Talents Program and the National Natural Science Foundation of China. The researchers had no financial conflicts to disclose.