Myotonic dystrophy severity with respect to the outcome measures

Progressive multisystem disorders of Myotonic dystrophy (MD) due to high number of repeats of Cytosine-Thymine-Guanine (CTG) or Cellular nucleic acid-binding protein (CCTG) in CNBP gene are one-dimensional measure of intensity of MD1, MD2 respectively. Manifestations of MD by multidimensional effects require appropriate aggregation method and validation with CTG/CCTG repeats. Management of symptoms by physical and occupational therapies and outcome measures are important for monitoring and treatment of MD. Outcome measures in ordinal scales containing K-point items like muscle impairment rating scale (MIRS) and other performance based measures in clinical trials suffer from methodological limitations. The paper suggests a method to convert ordinal item scores to continuous, equidistant scores following normal distribution and scale score (S-scores) as sum of such item scores. S-scores can be added to get battery scores (B-scores) reflecting MD severity with respect to the outcome measures. Normally distributed S-scores and B-scores satisfy desired properties, help to undertake parametric analysis to compare status and progression of patients and group of patients including assessment of effectiveness of treatment plans, equivalent scores of two scales and better estimates of reliability, validity and their relationships. The suggested B-scores reflecting MD severity with respect to the outcome measures is recommended.