title: A predictive model for diagnosing stroke-related apraxia of speech.
abstract: Diagnosis of the speech motor planning/programming disorder, apraxia of speech (AOS), has proven challenging, largely due to its common co-occurrence with the language-based impairment of aphasia. Currently, diagnosis is based on perceptually identifying and rating the severity of several speech features. It is not known whether all, or a subset of the features, are required for a positive diagnosis. The purpose of this study was to assess predictor variables for the presence of AOS after left-hemisphere stroke, with the goal of increasing diagnostic objectivity and efficiency. This population-based case-control study involved a sample of 72 cases, using the outcome measure of expert judgment on presence of AOS and including a large number of independently collected candidate predictors representing behavioral measures of linguistic, cognitive, nonspeech oral motor, and speech motor ability. We constructed a predictive model using multiple imputation to deal with missing data; the Least Absolute Shrinkage and Selection Operator (Lasso) technique for variable selection to define the most relevant predictors, and bootstrapping to check the model stability and quantify the optimism of the developed model. Two measures were sufficient to distinguish between participants with AOS plus aphasia and those with aphasia alone, (1) a measure of speech errors with words of increasing length and (2) a measure of relative vowel duration in three-syllable words with weak-strong stress pattern (e.g., banana, potato). The model has high discriminative ability to distinguish between cases with and without AOS (c-index=0.93) and good agreement between observed and predicted probabilities (calibration slope=0.94). Some caution is warranted, given the relatively small sample specific to left-hemisphere stroke, and the limitations of imputing missing data. These two speech measures are straightforward to collect and analyse, facilitating use in research and clinical settings.
authors.affiliation: Faculty of Health Sciences, University of Sydney, NSW, Australia.
authors.forename: Kirrie J
authors.initials: KJ
authors.lastname: Ballard
authors.affiliation: School of Public Health, Screening & Test Evaluation Program, University of Sydney, NSW, Australia.
authors.forename: Lamiae
authors.initials: L
authors.lastname: Azizi
authors.affiliation: Division of Speech Pathology, Department of Neurology, Mayo Clinic Rochester, MN, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Duffy
authors.affiliation: Department of Communication Sciences & Disorders, University of Pittsburgh, PA, USA; Veterans Administration, Pittsburgh Healthcare System, Pittsburgh, PA, USA.
authors.forename: Malcolm R
authors.initials: MR
authors.lastname: McNeil
authors.affiliation: Faculty of Health Sciences, University of Sydney, NSW, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Halaki
authors.affiliation: Faculty of Health Sciences, University of Sydney, NSW, Australia.
authors.forename: Nicholas
authors.initials: N
authors.lastname: O'Dwyer
authors.affiliation: Faculty of Health Sciences, University of Sydney, NSW, Australia.
authors.forename: Claire
authors.initials: C
authors.lastname: Layfield
authors.affiliation: Faculty of Health Sciences, University of Sydney, NSW, Australia.
authors.forename: Dominique I
authors.initials: DI
authors.lastname: Scholl
authors.affiliation: Centre for Neuroscience of Speech, The University of Melbourne, Australia; Department of Neurodegeneration, Hertie Institute for Clinical Brain Research, Eberhard Karls Universidad Tübingen, Germany.
authors.forename: Adam P
authors.initials: AP
authors.lastname: Vogel
authors.affiliation: Research Imaging Institute, Department of Neurology, and Joint Program in Biomedical Engineering, University of Texas Health Science Center San Antonio, TX, USA; Honors College, University of Texas, San Antonio, TX, USA.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Robin
mesh_terms: D000328:Adult; D000368:Aged; D001072:Apraxias / Q000175:diagnosis* / Q000209:etiology*; D001315:Australia; D015331:Cohort Studies; D005133:Eye Movements / Q000502:physiology; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009483:Neuropsychological Tests; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D020521:Stroke / Q000150:complications*
keywords: Aphasia; Apraxia of speech; Diagnosis; Lexical stress; Speech motor control; Stroke