Minimal Detectable Change of Cough and Lingual Strength Outcomes in Neurodegenerative Disease.

OBJECTIVE

Minimal detectable change (MDC) represents the smallest amount of change required for an outcome to be considered real and not merely due to measurement error or task variability. This study aimed to examine MDC for cough and lingual strength outcomes among individuals with neurodegenerative disease.

METHODS

In a single session, individuals diagnosed with Parkinson's disease (PD), progressive supranuclear palsy (PSP), and cerebellar ataxia completed repeated measurements of voluntary sequential cough via spirometry (n = 143) and lingual isometric and swallowing pressure with the Iowa Oral Performance Instrument (n = 231). The MDC at the 95% confidence level was calculated with the following formula: MDC = 1.96 × √2 × SEM.

RESULTS

MDC for cough strength was 0.52 L/s (PD), 0.57 L/s (PSP), and 0.20 L/s (ataxia). On trials with the same number of coughs, MDC for cough strength was 0.18 L/s in PD and 0.24 L/s in ataxia. MDC for lingual isometric pressure was 5.44 kPa (PD), 2.35 kPa (PSP), and 3.41 kPa (ataxia), whereas swallowing pressure was 5.60 kPa (PD), 2.97 kPa (PSP), and 7.34 kPa (ataxia).

CONCLUSIONS

These findings elucidate MDC for cough and lingual strength outcomes and expand our understanding of change that can be considered "real" and not merely due to task variability. MDC facilitates valid interpretations of changes following treatment, as well as power analyses to determine the smallest effect size of interest before data collection. To illustrate the application of MDC, we situate these findings in the context of hypothetical case studies and research studies.

LEVEL OF EVIDENCE: 3 Laryngoscope, 134:5034-5040, 2024.