Patients with neurodegenerative diseases affecting the frontal lobes have difficulties in categorization tasks, such as the similarity tasks. They give two types of unusual response to the question: “In what way are an orange and a banana alike?”, either a differentiation (“one is yellow, the other is orange”) or a concrete similarity (“they are sweet”).Objective:
To characterize the categorization deficit of frontal patients and develop a short diagnostic tool to assess the nature of these difficulties.Method:
We analyzed the responses provided by frontal and non-frontal neurodegenerative patients in a novel verbal similarity task (SimiCat). We included 40 frontal patients with behavioral variant fronto-temporal dementia (bvFTD) and progressive supranuclear palsy (PSP), 23 patients with Alzheimer's disease (AD) and 41 healthy matched controls. Responses that did not correspond to the expected taxonomic category (e.g.: fruits) were considered as errors.Results:
All patients groups were impaired at the SimiCat test compared to controls. Differentiation errors were specific to frontal patients. Receiver operating characteristic analyses showed that a cut-off of two differentiation errors or more achieved 85% sensitivity of 100% specificity to discriminate bvFTD from AD. A short version of the test (<5 min) showed similar discriminative validity as the full version.Conclusion:
Differentiation responses were specific to frontal patients. The SimiCat demonstrates good discriminative validity to differentiate between bvFTD and AD. The short version of the test is a promising diagnostic tool that will need validation in future studies.