The reliability of the modified Manual Muscle Test for persons with MS

Background Multiple sclerosis (MS) presents various symptoms, such as weakness, spasticity, ataxia, and reduction in sensory function. Traditional manual muscle strength tests may be biased due to the influence of spasticity. The modified Manual Muscle Test (mMMT) for people with MS (pwMS) was developed to take spasticity into consideration. This study aimed to evaluate the intra- and interrater reliability of the mMMT, as well as the influence of fatigue and spasticity on test results. Methods Six raters examined 28 pwMS in this single-centre, prospective, cross-sectional, and longitudinal study with a test-retest design. The muscle strength tests for dorsal foot flexion, hip flexion, and elbow flexion were used. Testing and retesting were conducted within 4 hours. Fatigue was assessed using the Fatigue Scale for Motor and Cognitive Functions and a numeric rating scale. Spasticity was evaluated using the Modified Tardieu Scale. The interrater reliability of the mMMT was evaluated by the intraclass correlation coefficient using one-way random effects ANOVA models. The intrarater reliability was estimated using two-way random effects ANOVA models. Models were adjusted for spasticity and rating order as a proxy for fatigue. Results The interrater reliability of the mMMT was poor. The results varied between raters and muscle groups. However, the intrarater reliability was good (overall intraclass correlation coefficient, 0.77). Fatigue or spasticity did not affect the test results. Conclusion The mMMT may be a reliable measure of muscle function in MS when applied by the same healthcare professional. We cautiously conclude that it may be possible to test selective muscle function in the presence of spasticity, reducing its influence on muscle strength testing in pwMS. This study also highlights the importance of rater training and the development of test protocols for each muscle group separately. Trial Registration ClinicalTrials.gov ID NCT03603691. Initial registration date 06/19/2018.