Social withdrawal in major depressive disorder: a case-control study of hikikomori in japan

•This study is among the first to characterize prolonged social withdrawal (hikikomori) among patients with major depressive disorder in Japan.•Social withdrawal can be a major indicator of impairment in social functioning and social relationships among patients with hikikomori and major depressive disorder.•Clinical investigation and research examining the phenotype of social social withdrawal in major depressive disorder is needed. Social withdrawal is a feature of a number of psychiatric disorders including major depressive disorder (MDD), yet research examining social withdrawal as a feature of MDD is rare. This was a retrospective case-control study. Participants (N = 67) were recruited through an outpatient clinic at an academic medical center in Japan. Major depressive disorder (MDD) and social withdrawal were established with the Structured Clinical Interview for DSM-IV Axis I Disorders and a semi-structured psychiatric interview, respectively. Participants also completed self-report measures. We classified 24 participants as cases (MDD with social withdrawal) and 43 participants as controls (MDD without social withdrawal). Cases, on average, were more likely to have lower education level, prior episodes of depression, and higher suicidal ideation at baseline than controls. In unadjusted regression models, cases had significantly less social connection, less reward dependence, less self-directedness, and higher scores on scales of modern-type depression and hikikomori. In adjusted regression models, associations between social withdrawal and hikikomori (p