Objective: While the Kraepelinian dichotomy explicitly distinguishes between schizophrenia and bipolar disorder, it remains unclear as to whether a deficit form of bipolar disorder exists. Method: We conducted a study to investigate the prevalence rate of the deficit form of bipolar disorder; the criteria of which were basically adopted by the original proposal for schizophrenia that described the predominance of negative symptoms for over a year. Moreover, we presented a series of cases with deficit bipolar disorder to characterize its clinical pictures in detail. Results: Consecutive outpatients who visited one psychiatric hospital in Tokyo, Japan in March 2007 were evaluated cross-sectionally. Additionally, medical charts of inpatients who were hospitalized in the same hospital between April 2006 and March 2007 were also thoroughly reviewed. Of 494 patients, 7 patients (1.4%; 10.9% of 64 bipolar cases) fulfilled the criteria for bipolar disorder with deficit syndrome. Seven deficit cases had a mean±SD age of 61±5 year-old with the age at onset being 25±8 year-old. In addition to pervasive negative symptoms, they exhibited evidence of cognitive impairments close to the magnitude of what is usually noted in schizophrenia (i.e. a mean±SD total IQ score of 80±9 in the Wechsler Adult Intelligence Scale and 0.4±0.5 in the Wisconsin Card Sorting Test, categories achieved). Conclusion: Although preliminary, the evidence on deficit status in patients with bipolar disorder that we found in this study appears more consistent with recent evidence and challenges the Kraepelinian dichotomy that reserves deficit status solely to schizophrenia patients.
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