Background: As the number of internet users increases, problems related to internet overuse are becoming more and more serious. Adolescents and youth may be particularly attracted to and preoccupied with various online activities. In this study, we investigated the relationship of internet addiction, smartphone addiction, and the risk of hikikomori, severe social withdrawal, in Japanese young adult. Methods: The subjects were 478 college/university students in Japan. They were requested to complete the study questionnaire, which consisted of questions about demographics, internet use, the Internet Addiction Test (IAT), the Smartphone Addiction Scale (SAS)–Short Version (SV), the 25-item Hikikomori Questionnaire (HQ-25), etc. We investigated the difference and correlation of the results between two groups based on the purpose of internet use or the total score of each self-rating scale, such as screened positive or negative for the risk of internet addiction, smartphone addiction, or hikikomori. Results: There was a trend that males favored gaming in their internet use while females used the internet mainly for social networking via smartphone, and the mean SAS-SV score was higher in females. Two-group comparisons between gamers and social media users, according to the main purpose of internet use, showed that gamers used the internet longer and had significantly higher mean IAT and HQ-25 scores. Regarding hikikomori trait, the subjects at high risk for hikikomori on HQ-25 had longer internet usage time and higher scores on both IAT and SAS-SV. Correlation analyses revealed that HQ-25 and IAT scores had a relatively strong relationship, although HQ-25 and SAS-SV had a moderately weak one. Discussion: Internet technology has changed our daily lives dramatically and altered the way we communicate as well. As social media applications are becoming more popular, users are connected more tightly to the internet and their time spent with others in the real world continues to decrease. Males often isolate themselves from the social community in order to engage in online gaming while females use the internet as to not be excluded from their communications online. Mental health providers should be aware of the seriousness of internet addictions and hikikomori.

Aim Hikikomori, a form of severe social withdrawal, is an emerging issue in mental health, for which validated measurement tools are lacking. The object was to develop a self‐report scale of hikikomori, and assess its psychometric properties and diagnostic accuracy.MethodsA sample of 399 participants from clinical and community settings completed measures. Psychometric properties were assessed with factor analysis; diagnostic accuracy was compared against a semi‐structured diagnostic interview.ResultsThe Hikikomori Questionnaire contained 25 items across three subscales representing socialization, isolation, and emotional support. Internal consistency, test–retest reliability, and convergent validity were all satisfactory. The area under the curve was 0.86 (95% confidence interval, 0.80–0.92). A cut‐off score of 42 (out of 100) was associated with a sensitivity of 94%, specificity of 61%, and positive predictive value of 17%.ConclusionThe 25‐item Hikikomori Questionnaire (HQ‐25) possesses robust psychometric properties and diagnostic accuracy in an initial sample of Japanese adults. Additional research on its psychometric properties and ability to support clinical assessment of hikikomori is warranted.

Aim Understanding premorbid personality is important, especially when considering treatment selection. Historically, the premorbid personality of patients with major depression in Japan was described as Shuchaku‐kishitsu [similar to Typus melancholicus], as proposed by Shimoda in the 1930s. Since around 2000, there have been increased reports in Japan of young adults with depression who have had premorbid personality differing from the traditional type. In 2005, Tarumi termed this novel condition ‘dysthymic‐type depression,’ and more recently the condition has been called Shin‐gata/Gendai‐gata Utsu‐byo [modern‐type depression (MTD)]. We recently developed a semi‐structured diagnostic interview to evaluate MTD. Development of a tool that enables understanding of premorbid personality in a short time, especially at the early stage of treatment, is desirable. The object of this study was to develop a self‐report scale to evaluate the traits of MTD, and to assess the scale's psychometric properties, diagnostic accuracy, and biological validity. Methods A sample of 340 participants from clinical and community settings completed measures. Psychometric properties were assessed with factor analysis. Diagnostic accuracy of the MTD traits was compared against a semi‐structured interview. Results The questionnaire contained 22 items across three subscales, thus we termed it the 22‐item Tarumi's Modern‐Type Depression Trait Scale: Avoidance of Social Roles, Complaint, and Low Self‐Esteem (TACS‐22). Internal consistency, test–retest reliability, and convergent validity were all satisfactory. Among patients with major depression, the area under the curve was 0.757 (sensitivity of 63.1% and specificity of 82.9%) and the score was positively correlated with plasma tryptophan. Conclusion The TACS‐22 possessed adequate psychometric properties and diagnostic accuracy in an initial sample of Japanese adults. Additional research on its ability to support clinical assessment of MTD is warranted.

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Aim: Hikikomori, a form of pathological social withdrawal, has been suggested to have comorbidity with autism spectrum disorder (ASD). This study aimed to clarify how characteristics of hikikomori are associated with ASD, including undiagnosed autism spectrum conditions (ASC), in clinical settings. Methods: A total of 416 clinical patients were recruited through the Mood Disorder/Hikikomori Clinic at Kyushu University Hospital. A total of 103 hikikomori cases and 221 clinical controls without hikikomori conditions were extracted using a semi-structured interview, and completed a series of self-rated scales, including the Japanese version of the Autism-Spectrum Quotient (AQ-J). Results: Compared to non-hikikomori controls, hikikomori cases were more likely to have higher autistic tendency based on the AQ-J. The cases showed more severe subjective depressive symptoms based on the self-rated Beck Depression Inventory II, whereas no significant difference was found on interview-based severity evaluation using the Hamilton Depression Rating Scale. Comparison within hikikomori cases based on the AQ-J cutoff score revealed that hikikomori cases with high ASC were significantly more likely to have higher traits of modern-type depression, smaller social networks, and less social support. Conclusion: The present data suggest that hikikomori sufferers are more likely to have autistic tendency, and that hikikomori sufferers with high ASC may have much more difficulty in social communication and social interaction. In addition, those with high ASC may also have lower selfesteem and higher complaint tendencies as aspects of modern-type depression traits, which may relate to the occurrence of hikikomori. Thus, evaluating autistic tendencies is important for appropriate interventions in hikikomori. Further investigations should be conducted to validate our pilot findings using structured diagnostic systems of ASD.