Prefrontal dysfunction in remitted depression at work reinstatement using near-infrared spectroscopy

A long-term and/or recurrent sickness absence from work due to depression has been an important health problem in industrial countries. In addition, previous sick leave is a risk factor of recurrence. However, many characteristics, especially biological aspects, have not been investigated in remitted depressive patients who were ready to return to work from sickness absence. Therefore, the purpose of this study is to clarify the pathophysiological characteristics of patients who were at risk for recurrence of sickness absence. We recruited 21 patients and 16 healthy control subjects. All patients were ready to return to work within one month from long-term sickness absence. All subjects were examined for prefrontal function represented by oxyHb changes during the verbal fluency task (VFT) and the Stroop task using near-infrared spectroscopy. Suppressed prefrontal reaction during the VFT and increased prefrontal reaction during the Stroop task were observed in the patient group compared with the control group. Significantly lengthened reaction time was observed in the incongruent condition in the patient group during the Stroop task. Depressive patients showed impaired executive function measured by the Stroop task and had prefrontal dysfunction despite clinical remission. Residual prefrontal dysfunction may be one biological reason for repetitive sickness absence.