The Effect of Creatine Supplementation on Muscle Function in Childhood Myositis

This project will bring together a multidisciplinary team of pediatric rheumatologists, neurologists, metabolic geneticists and exercise physiologists to determine the effect of creatine (CR) supplementation on muscle function and muscle metabolism in children with Dermatomyositis (DM). The investigators propose using well-established exercise testing techniques as well as new, powerful exercise imaging protocols in order to better delineate the effects of CR on muscle pathophysiology in a non-invasive way. Evidence from this study will provide information regarding the effect of creatine supplementation on muscle function in DM. Improvements in muscle function and fatigue through CR use may also contribute to an improvement in quality of life and have significant clinical implications for the treatment of children with DM.

Patients will be prescribed a creapure supplement by weight, to be taken 3x/day for the duration of the trial. They will be randomized to an active product start time using a multiple baseline design.

Patients will be prescribed the placebo supplement by weight, to be taken 3x/day for the duration of the trial. They will be randomized to an active product start time using a multiple baseline design.

The effects of creatine supplementation on key metabolites responsible for proper energy shuttling in healthy muscle will be measured at rest and using exercise protocols in subjects with P-MRS.

Both overall and health-related quality of life will be measured at each study visit with the Quality of My Life scale.

Will be measured using the International Myositis Assessment and Clinical Studies Group (IMACS) before and after creatine supplementation

Will be determined using the PedsQL fatigue module which has been validated for use in children with fibromyalgia and rheumatic disease.

This will be assessed based on a positive blood plasma and urine tests for creatine use over the course of the study period, amount of medication remaining and through self-reports using study diaries.

Inclusion Criteria: Ages 7 to 18 years Diagnosis of probable JDM (onset <16 years) according to Bohan and Peter criteria Subjects on a stable course of medication (unlikely to change over study treatment period as determined by the treating physician) Minimum height of 132.5cm Exclusion Criteria: Subjects newly diagnosed with JDM within the previous 6 months Subjects unable to cooperate with study procedures, or too weak to participate in the exercise testing Subjects with impaired kidney function as determined from baseline visit screening lab values Subjects who are currently pregnant or planning to become pregnant within the study period Subjects who are shorter than 132.5cm