A longitudinal physical profile assessment of skeletal muscle manifestations in myotonic dystrophy

To develop an assessment that describes the skeletal muscle manifestations in myotonic dystrophy subjects and then use it to quantify the presentation of skeletal muscle disability and to show change over time.

A quantified skeletal muscle assessment was developed and applied three times over a two-year period at intervals around 12 months. Thirty-six subjects with myotonic dystrophy and 20 subjects without neuromuscular disability were evaluated. The assessment comprised manual muscle testing of five pairs of muscles, measuring neck flexor strength with a strain gauge, respiratory function tests, power and lateral pinch grip strength, all tests of impairment. Assessment of the ability to move from sitting to standing and fasten buttons tested disability.

Results from subjects with myotonic dystrophy were compared to the normal data. The subjects with myotonic dystrophy were significantly weaker in proximal upper limb muscles, quadriceps, tibialis anterior muscles and neck flexor muscles as well as power and lateral pinch grips. There was also significant reduction in forced expiratory volume at one second (FEV1) and forced vital capacity (FVC). Significant disability was seen in the myotonics in moving from sitting to standing and in fastening buttons. Over the two-year study period proximal upper limb and lower limb muscle strength, FVC and sit-to-stand ability declined significantly. Power grip declined but lateral pinch grip and FEV1 improved significantly. Button fastening ability improved significantly.

The test developed was shown to be reliable and sensitive to the change in skeletal muscle manifestations in subjects with myotonic dystrophy who were shown to be significantly weaker than normal subjects.