Unclassified cases of behavioral variant of major frontotemporal neurocognitive disorder in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition.

AIM: In the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), the behavioral variant of major frontotemporal neurocognitive disorder (bvFT-NCD) is subclassified into "probable bvFT-NCD" or "possible bvFT-NCD." When genetic evidence is unavailable, cases without clinical neuroimaging are subclassified into "possible bvFT-NCD," whereas cases whose clinical images show the typical characteristics are subclassified into "probable bvFT-NCD." Thus, the cases that meet the diagnostic criteria of bvFT-NCD based on their symptoms, but lack the neuroimaging characteristics, fall between the two categories of probable and possible bvFT-NCD. These cases herein are defined as "unclassified bvFT-NCD," and the present study aims at considering an appropriate diagnostic approach to such cases, that is, whether unclassified bvFT-NCD should be included in bvFT-NCD as a third subcategory, or whether it should be classified into diseases other than bvFT-NCD.

METHODS: All patients who presented at the Department of Psychiatry of the National Center for Geriatrics and Gerontology with suspicion of the behavioral variant of frontotemporal dementia between 1 May 2011 and 30 April 2013 were retrospectively rediagnosed based on the DSM-5 criteria.

RESULTS: A total of 16 cases met the criteria of bvFT-NCD, and among them, eight cases corresponded to unclassified bvFT-NCD. From a cross-sectional and clinical perspective, all eight cases of unclassified bvFT-NCD fulfilled the symptomatic criteria for bvFT-NCD, although the possibilities of Alzheimer's disease and other mental disorders could not be ruled out completely.

CONCLUSIONS: To establish clinical diagnostic criteria for unclassified bvFT-NCD, accumulation of cases and evidence will be required along with longitudinal observation using various diagnostic technologies and post-mortem examination.