Jenny Lin, Durga Shah, Courtney McCracken, Sumit Verma
Multi-motor unit analysis (MMA) to study myopathy in DMD.
Six-Minute Walk Test (6MWT) and North Star Ambulatory Assessment (NSAA) in DMD are limited by patient motivation. Quantitative EMG (MMA) is a sensitive marker of muscle disease severity and has been used in inclusion body myositis to study disease progression. We hypothesized that MMA would be sensitive to study disease progression in DMD.
Prospective study of 17 ambulatory Duchenne boys enrolled from MDA clinic over one year. IRB approval and written consent obtained. 6MWT, NSAA, Vignos, and EMG data were collected at enrollment and 6 months. Twenty motor unit potentials (MUP) were analyzed using MMA software (Synergy, Natus) in the right biceps brachii (BB) and tibialis anterior (TA) muscles respectively. Correlation coefficients were measured between EMG measurements and functional scores. Wilcoxon signed-rank tests were used to compare change of measurements over time.
Mean age was 8.5+2.6 years (range 5-14). Baseline average 6MWT (255+152m), NSAA (18.9+9.0), Vignos (1.8+0.7) and MMA MUP (duration BB 4.5ms, TA 6ms; area/amplitude ratio BB 0.9, TA 1.1; phases/turns BB 2.7/2.8, TA 3/3.6) was obtained. Eleven Duchenne boys had repeat evaluations after six months. Follow-up average 6MWT (298+179m), NSAA (18.1+12.8), Vignos (2.9+3.1) and MMA MUP (duration BB 4.8ms, TA 6.7ms; area/amplitude ratio BB 0.9, TA 1.2; phases/turns BB 2.5/2.9, TA 3.2/3.6) showed no significant interval change. MUP duration of BB and TA were below two standard deviations of the normal mean. Phases and turns on MMA (BB) correlated strongly with NSAA (>0.5).
Quantitative EMG (MMA) was abnormal in DMD boys, and the results correlated significantly with functional scores (NSAA). Interval change in MUP parameters at six months follow-up was not statistically significant; however the study is limited by the short time frame for a chronic disease.
Rehabilitation Children's Healthcare of Atlanta, USA; Emory University School of Medicine, USA