Persistent depression, or “trait” depression, was significantly higher in patients with schizophrenia than in controls, and was associated with more severe psychosis, a study showed.

Trait depression was not, however, associated with cognitive impairment or decreased white matter integrity, wrote Dr. Joshua J. Chiappelli and his colleagues.

Characterized by “the tendency to experience negative emotions and distressing thoughts” consistently over time, trait depression is distinct from state depression, which includes only current symptoms, said the investigators, who are affiliated with the Maryland Psychiatric Research Center at the University of Maryland in Baltimore.

The study authors examined the association of trait depression with cognitive deficits, functional capacity impairment, and white matter integrity in 126 patients and 151 controls recruited from the Maryland Psychiatric Research Center. Participants completed the Maryland Trait and State Depression ( MTSD ) questionnaire, which asked 36 questions about the frequency of depressive symptoms over the past week (state questions) and over the course of adult life (trait questions). Cognition was assessed using the Digit Symbol Coding task of the Wechsler Adult Intelligence Scale and the Digital Sequencing task from the Brief Assessment of Cognition in Schizophrenia .

White matter integrity was determined by the measure of fractional anistropy (FA) on a diffusion MRI (Schizophr. Res. 2014;159:243-8).

Severity of both trait and state depression in schizophrenia patients was significantly and positively associated with scores on the Brief Psychiatric Rating Scale (rho = 0.246, P = .005; rho = 0.312, P <.001, respectivley). However, a higher MTSD score was not associated with severe cognitive deficits; in fact, severe trait depression was significantly associated with working memory, processing speed, and functional capacity (rho = 0.186, P = .044; rho=0.206, P = .024; rho = 0.220, P = .017, respectively).

Whole brain FA values were higher in controls than in patients with schizophrenia (FA = 11.86, P = .001). In addition, higher trait depression scores were significantly associated with higher FA values in schizophrenia patients.

“These findings appear paradoxical, especially when examined in comparison to major depressive disorder,” as severity is typically linked to worse cognition, the study authors wrote.

These findings “raise an interesting question on whether trait depression is a relatively separate clinical domain,” compared with major depressive symptoms, or other clinical measures in schizophrenia, the investigators added.

One limitation of the study was possible recall bias in the measure of trait depression, the authors said. In addition, patients who were on antidepressant medication had higher levels of trait depression.

The authors reported no relevant financial disclosures. The study was funded by a grant from the National Institutes of Health.