Functional Ability in Non-ambulatory People with Duchenne Muscular Dystrophy or Spinal Muscular Atrophy
Abstract af Birgit Steffensen
Duchenne muscular dystrophy (DMD) and spinal muscular atrophy (SMA) are neuromuscular diseases charachterised by profound global skeletal muscle weakness leading to severe physical disability. The EK scale was developed to assess functional ability in non-ambulatory individuals with DMD or SMA.
This study aimed at examining the properties of the EK scale with respect to reliability, validity and the ability to predict the need for assisted ventilation.
Reliability: Different healthcare professionals assessed six video recorded individuals with DMD who were tested with the EK scale. A reliability coefficient of 0.98 was found of both inter- and intrarater reliability and a variation of ± 1.5 EK sum units when the same evaluators repeated the assessments a second time and of ± 1.9 when different evaluators measured once.
Since no gold standard existed construct validity was tested by examining the relationship between measures of muscle strength, Forced Vital Capacity in % of normal (FVC%), sum of contractures and years of wheelchair dependence and the EK scale. A close relationship was found between muscle strength and EK sum in both diagnoses when the subjects were assessed only once. Over time there was a similarly close relationship between these variables among subjects with DMD but a weak relationship in subjects with SMA. Among subjects with DMD there was a significant change of EK sum over five years in contrast to subjects with SMA. EK sum changed due to intervention with spinal bracing or surgery in subjects with DMD after one year whereas in subjects with SMA EK sum did not change. Among subjects with DMD all categories had deteriorated whereas among subjects with SMA only five categories had deteriorated and one category had improved.
Examination of content validity showed that approximately all categories were used for scoring in both diagnostic groups. The sequence in which the individual categories changed over time was characteristic for each diagnosis and similar when examined in a cross sectional design and a longitudinal design.
Six different respiratory measures, EK sum and a clinical assessment instrument: EAMDA sum were examined with respect to their ability to predict the need for assisted ventilation in subjects with DMD. A combination of EK sum >20 and FVC% < 30 were the only measures which identified the individuals with DMD.
It was concluded that the EK scale was able to discriminate between individuals with DMD or SMA of different functional ability. EK sum was less sensitive to assess changes due to the natural history over shorter than one year, however, it was able to assess changes due to treatment of scoliosis and the EK sum could together with FVC% predict the need for assisted ventilation in subjects with DMD.
Key words: Duchenne muscular dystrophy, spinal muscular atrophy, non-ambulatory stage, EK scale, reliability, validity, natural history, functional ability, scoliosis, treatment.