Background: Formal olfactory testing may be useful as a bedside tool to help differentiate between conditions such as atypical parkinsonism, dementia, and psychiatric conditions. However, the neural basis of olfactory dysfunction, the effect of concurrent cognitive deficits on olfactory testing results, and the exact prevalence of olfactory deficits in populations with corticobasal syndrome (CBS) and the frontal variant of frontotemporal dementia (FTD-FV) are to date unclear.
Objective: To assess the prevalence and the neural basis of olfactory recognition deficits in patients with a clinical diagnosis of CBS or FTD-FV.
Design: Retrospective study of clinical, neuropsychological, and imaging data.
Setting: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
Participants: Twenty-five patients with CBS, 22 with FTD-FV, and 12 age-matched control subjects.
Main outcome measures: Results of neuropsychological evaluation, formal olfactory recognition testing (University of Pennsylvania Smell Identification Test [UPSIT]), and voxel-based morphometry analysis of structural magnetic resonance images of the brain.
Results: Mean UPSIT percentile scores were 31.6% for the CBS group and 9.5% for the FTD-FV group. The voxel-based morphometry correlations between local gray matter and UPSIT scores showed a significant volume effect in the right midfrontal gyrus for the FTD-FV patients and in the right insula, right midfrontal gyrus, and bilateral inferior frontal gyrus for the patients with CBS. A linear regression analysis of the UPSIT scores revealed as significant predictors the general memory score of the Wechsler Memory Scale and the Boston Naming Test total score for the patients with FTD-FV and the Mattis Dementia Rating Scale total score for the patients with CBS.
Conclusions: Our data showed a more severe olfactory impairment for CBS patients than previously reported. We also showed a significant relationship between formal olfactory recognition testing scores and specific cognitive domains. These findings could be useful to clinically differentiate FTD-FV and CBS from other dementing illnesses and movement disorders.