Assessment of orofacial strength in patients with dysarthria

Assessment of orofacial weakness is common during the evaluation of patients with suspected dysarthria. This study addressed the validity of clinical assessments of orofacial weakness by comparing clinical (subjective) ratings to instrumental (objective) measures. Fortyfour adults referred to a speech pathology clinic for dysarthria evaluation were tested for strength of the tongue during elevation, lateralization, and protrusion, and for the strength of the muscles of the lower face during buccodental and interlabial compression. Subjective assessment of weakness involved rating maximum resistance against a firmly held tongue depressor, using a 5-point scale. Objective assessment involved the Iowa Oral Performance Instrument (IOPI), measured as the maximal pressure generated against an air-filled bulb. A recent adaptation to the IOPI permitted testing of tongue and cheek strength using tasks that are comparable to the subjective tasks. Moderate correlations were found between the objective and subjective evaluations, with the strongest correlations for tongue lateralization. Lower pressure values were associated with higher subjective ratings of weakness for each task, although there was substantial overlap in the data. These results, combined with the notion that examiner bias is inherent to clinical assessment, support the use of instrumentation to improve objectivity and precision of measurement in the clinic.