A Systematic Review and Meta-analysis of Iowa Oral Performance Instrument Measures in Persons with Parkinson's Disease Compared to Healthy Adults.

Measures of tongue strength and endurance using the Iowa Oral Performance Instrument (IOPI) may have diagnostic utility during clinical swallowing evaluations for persons with Parkinson's disease (PwPD). Thus, the objective was to systematically analyze the existing literature comparing IOPI values of tongue strength and endurance between age- and sex-match pairs of PwPD and healthy adults as well as across disease stages. A systematic review of 12 databases and Google Scholar identified five peer-reviewed articles published in English (1990-2019) that compared tongue strength and/or endurance between PwPD and controls. Individual-level data were published in two studies and provided by authors for three studies. Study appraisal included the NIH Quality Assessment Tool and STROBE checklists. Limited data for posterior tongue pressures restricted meta-analyses to anterior pressures. Meta-analyses of group means indicated reduced tongue strength across 106 matched pairs (p < .001, I2 = 0%) and a trend for reduced endurance across 41 matched pairs (p = .07, I2 = 54%). Participant-level analyses found reduced strength (96 pairs, p < .001) and endurance (41 pairs, p = .011) secondary to PD. Tongue strength (n = 68), but not endurance (n = 41), inversely correlated with disease stage when controlling for age (p ≤ .018). Overall, clinicians should be aware that reduced anterior tongue strength and endurance are as follows : expected in approximately one-third and one-fourth of PwPD, respectively, and reduced anterior tongue strength may manifest as early as Hoehn and Yahr stage 2 with continual decline as disease progresses. Further investigation is warranted regarding the relation among tongue strength, tongue endurance, and swallowing physiology as well as applications of tongue pressure training within dysphagia rehabilitation for PwPD.