Clinical usefulness of the Verbal Fluency Index (VFI) in amyotrophic lateral sclerosis

This study aimed at assessing the clinical utility of the Verbal Fluency Index (VFI) over a classical phonemic verbal fluency test in Italian-speaking amyotrophic lateral sclerosis (ALS) patients.

N = 343 non-demented ALS patients and N = 226 healthy controls (HCs) were administered the Verbal fluency - S task from the Edinburgh Cognitive and Behavioural ALS Screen (ECAS). The associations between the number of words produced (NoW), the time to read words aloud (TRW) and the VFI (computed as [(60"-TRW)/NoW]) on one hand and both bulbar/respiratory scores from the ALS Functional Rating Scale - Revised (ALSFRS-R) and the ECAS-Executive on the other were tested. Italian norms for the NoW and the VFI were derived in HCs via the Equivalent Score method. Patients were classified based on their impaired/unimpaired performances on the NoW and the VFI (NoW-VFI-; NoW-VFI+; NoW + VFI-; NoW + VFI+), with these groups being compared on ECAS-Executive scores.

The VFI, but neither the NoW nor the TRW, were related to ALSFRS-Bulbar/-Respiratory scores; VFI and NoW measures, but not the TRW, were related to the ECAS-Executive (p < .001). The NoW slightly overestimated the number of executively impaired patients when compared to the VFI (31.1% vs. 26.8%, respectively). Patients with a defective VFI score - regardless of whether they presented or not with a below-cutoff NoW - reported worse ECAS-Executive scores than NoW + VFI + ones.

The present reports support the use of the Italian VFI as a mean to validly assess ALS patients' executive status by limiting the effect of motor disabilities that might undermine their speech rate.