Alterations in regional homogeneity of resting-state brain activity in patients with major depressive disorder screening positive on the 32-item hypomania checklist (HCL-32)

Background:
Bipolar disorder (BD) is difficult to diagnose in the early stages of the illness, with the most frequent misdiagnosis being major depressive disorder (MDD). We aimed to use a regional homogeneity (ReHo) approach with resting-state functional magnetic resonance imaging (rs-fMRI) to investigate the features of spontaneous brain activity in MDD patients screening positive on the 32-item Hypomania Checklist (HCL-32).

Methods:
Nineteen MDD patients screening positive (HCL-32(+); 9 males; 24.9 ± 5.7 years) and 18 patients screening negative (HCL-32(-); 9 males; 27.1 ± 6.7 years), together with 24 healthy controls (HC; 11 males; 26.4 ± 3.9 years) were studied. ReHo maps were compared and an receiver operating characteristic (ROC) analysis was conducted to confirm the utility of the identified ReHo differences in classifying the patients. Results The MDD versus HC showed different ReHo in many brain areas, especially in the frontal and parietal cortex. The HCL-32(+) versus HCL-32(-) showed significant increase of ReHo in the right medial superior frontal cortex, left inferior parietal cortex and middle/inferior temporal cortex, and decrease of ReHo in the left postcentral cortex and cerebellum. ROC analysis showed good sensitivity and specificity for distinguishing these two subgroups of MDD. Limitations Recruited patients were all on antidepressants and standard mania rating scales were not used to assess their hypomanic symptoms.

Conclusions:
The rs-fMRI measurement of ReHo in distributed brain regions may be putative biomarkers which could differentiate subthreshold BD from MDD.