Serial manual muscle testing in Duchenne muscular dystrophy

Serial measurements of muscle strength of 34 muscle groups were obtained for up to a seven-year period using manual muscle testing (MMT) in a group of 63 boys (mean age = 11.5 years) with Duchenne muscular dystrophy (DMD) not using lower extremity bracing or corrective surgery for ambulation, in order to define the natural course of strength loss and its relation to anthropometric variables and ambulatory status. When correlating the first MMT assessment of each patient with age, strength was found to decrease linearly (-0.26 +/- 0.30 MMT units/year) with time until approximately age 14 when a marked decrease in progression was noted (-0.06 +/- 0.03 MMT units/year). Analyzing individual patients longitudinally yielded a similar rate of strength loss. The average muscle score was 3.0 MMT units at the point of full-time wheelchair use. The marked decline in MMT deterioration around age 14 may be an important consideration when assessing the efficacy of therapeutic interventions in adolescent boys with DMD.