Aim: When clinicians follow today's diagnostic trend which gives priority to mood disorders, they risk overlooking mild manifestations of schizophrenia-like symptoms. This study was aimed at investigating clinical features of patients with a prolonged depressive state for years, showing minute schizophrenia-like symptoms without any full-fledged psychotic symptoms.
 Method: The subjects were 170 male inpatients with depression or a depressive state who were admitted to Kyorin University Hospital between April 200X and March 200X+3. One of the reasons for their admission was to make a differential diagnosis. The diagnoses of fifteen patients (mean age at onset: 29.5±8.5 years, and mean age at their first visit to a psychiatrist: 34.3±10.0 years), who had been diagnosed with depression and treated with various kinds of antidepressants for years (mean period: 4.9±3.4 years) were changed to persistent depression with minute schizophrenia-like symptoms according to "pluridimensional assessment," which takes the following factors into consideration: a premorbid character, predicting situations or life events, clinical features, psychological tests, reactions to treatment, and the course and social outcome. The psychopathology of these fifteen patients was closely investigated.
 Results: The investigation revealed that: 1) All patients had a premorbid "schizoid tendency", which was defined as more than two of three character markers of "Schizothymie", described by E. Kretschmer. 2) Most of the patients clinically manifested after low-level psychosocial stress had activated hypersensitivity to the surroundings. 3) In addition to depressive symptoms delineated in Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR), clinical features included repeated physical complaints, which were poorly explained, suicidal behaviors without any understandable conflicts, unexpected arrogant attitudes toward medical staff and other patients, and superficial, simplistic, and monotonous speech and odd thoughts. They were regarded as minute symptoms of schizophrenia, which should not be overlooked. 4) They showed clear evidence of severe cognitive impairment in the Wechsler Adult Intelligence Scale third edition (WAIS-III) and in the Landscape Montage Technique (LMT). The results of these psychological tests, which should be assessed as reference materials in a clinical diagnosis, were low and bizarre when their remorbid social functioning was considered, which may be concordant with their latest defective social functioning. 5) Pharmacotherapy involving any kind of antidepressant had not been effective, and, in some patients switching to or adding antipsychotic drugs effectively reduced their minute schizophrenia-like symptoms, hypersensitivity, and loss of motivation. 6) Two patients committed suicide, three were demoted from regular to contractual employment, and the others are now undergoing rehabilitation together with schizophrenic patients in regional day-care and occupational therapy centers.
 Conclusions: Clinicians should explore the possibility that manifested mood changes conceal minute schizophrenia-like symptoms. Such patients should be pluridimensionally assessed. Therapeutic strategies for schizophrenic patients may be more appropriate for the patients investigated in this study.
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