Optimising verbal fluency analysis in neurological patients with dysarthria: examples from Parkinson’s disease and hereditary ataxia

ABSTRACT

Background

Verbal fluency tests (VFTs) are widely used to assess cognitive-linguistic performance in neurological diseases. However, the influence of dysarthria on performance in tests requiring oral responses is unclear in ataxia and Parkinson’s disease.

Objectives

To determine the impact of dysarthria on VFT performance and evaluate the validity and reliability of alternative methods for analyzing VFT data.

Method

Trained raters evaluated dysarthria using VFT recordings in people with ataxia (N = 61) or Parkinson’s disease (PD; N = 69). Total Correct Items scores and qualitative parameters (intrusions, ambiguous verbalizations, perseverations, and interjections) were compared across semantic, phonemic, and alternating fluency tasks. Disease severity was considered as a covariate in the regression model.

Results

VFT dysarthria ratings correlated with the benchmark (ground truth) dysarthria scores derived from a monologue. Ambiguous responses resulting from unclear speech impeded the rater’s ability to determine if a response was correct. Regression analysis indicated that more severe dysarthria ratings predicted diminished scores in all three tasks (semantic fluency, phonemic fluency and alternating fluency) in the ataxia group. The contribution of disease severity to semantic, phonemic and alternating fluency was reduced substantially in the ataxia group after accounting for dysarthria severity in the model in both groups.

Conclusions

Dysarthria severity can be estimated based on speech samples derived from VFT. Dysarthria can lead to lower total correct items and is associated with more ambiguous verbalizations in VFT. Dysarthria severity should be considered when interpreting VFT performance in common movement disorders.

KEYWORDS:

• Verbal fluency
• dysarthria
• Parkinson’s disease
• hereditary ataxias
• semantic fluency
• phonemic fluency
• alternating fluency

Acknowledgments

We thank all participants of the study, the Royal Brisbane and Women's Hospital Foundation for funding the original PD-MCI project in Queensland, and the core research team of the PD-MCI project including Professor Gerard Byrne, Professor David Copland, Dr Leander Mitchell, A/Prof John O’Sullivan and Professor Katie McMahon. A/Prof Dissanayaka is supported by the National Health and Medical Research Boosting Dementia Research Leadership Fellowship.

Disclosure of interest

Dr Vogel is the Chief Science Officer of Redenlab Inc. Miss Li is a Project Manager of Redenlab Inc.

Compliance with ethical standards

The present study received institutional ethical approval from the University of Melbourne (1,339,394.2), and University Hospital Tübingen, Germany (Az. 003/2015BO2). The human research ethics committees of the University of Queensland (2,015,001,881) and the Royal Brisbane and Women’s Hospital (HREC/15/QRBW/446) approved the PD-MCI project titled “Markers and Mechanisms of Mild Cognitive Impairment in Parkinson’s disease” with provision for de-identified data sharing under data sharing agreement executed for this study.

Informed consent

Informed consent was obtained from all participants included in the study.

Disclosure statement

Dr Vogel is Chief Science Officer of Redenlab Inc. Miss Li is Project Manager of Redenlab Inc.

Additional information

Funding

Dr Vogel received salaried support from the National Health and Medical Research Council, Australia (1082910) and institutional support from The University of Melbourne. A/Prof Dissanayaka was supported by the National Health and Medical Research Boosting Dementia Research Leadership Fellowship(APP1137339). Dr Yang was supported by an Australian Government Research Training Program Scholarship.