Reply

We appreciate the interest of Dr. Takken and colleagues in our recent publication, and we also appreciate the opportunity to respond to their comments. Takken et al first comment on the importance of distinguishing between CMAS results and the assessment of muscle strength. We agree that the CMAS is not solely a measure of muscle strength, and it is for this reason that we have recommended that it be used in conjunction with more direct measures of muscle strength, such as manual muscle testing (MMT). The CMAS is intended for the assessment of overall muscle function, and as such, the construct addresses not only muscle strength, but also functional performance and endurance. However, the high correlation between CMAS scores and results of MMT that we observed in our study indicates a substantial relationship between these 2 measures. As stated in our report, we believe the 2 measures complement one another when used together in the assessment of children with idiopathic inflammatory myopathy. With regard to Takken and colleagues' second comment, we agree that age and maximal oxygen uptake are likely to be important predictors of CMAS score. As previously reported by Hicks et al, CMAS scores correlate strongly with peak oxygen uptake during aerobic exercise (Hicks JE, Drinkard B, Summers RM, Rider LG. Decreased aerobic capacity in children with juvenile dermatomyositis. Arthritis Rheum 2002;47:118–23). However, we disagree with the statement that muscle strength is not a predictor of CMAS score. Our data showed a Spearman's rank correlation of 0.73 between muscle strength (as measured by MMT) and the CMAS score. This represents a substantial and important relationship between the 2 measures. Finally, Takken et al indicate that our data should have been corrected for age. We agree that age influences the ability to perform some items in the CMAS, as has recently been shown by Rennebohm et al (Rennebohm RM, Jones K, Huber AM, Ballinger SH, Bowyer SL, Feldman BM, et al. Normal scores for nine maneuvers of the Childhood Myositis Assessment Scale. Arthritis Rheum 2004;51:365–70). Unfortunately, at this time there are no age-matched normal values for the CMAS. We used data from the report by Rennebohm et al to compare scores on 9 items of the CMAS in 4–9-year-old juvenile dermatomyositis patients and age- and sex-matched healthy control children. Our study showed that children with juvenile dermatomyositis who had abnormal scores on the 9-item CMAS had worse physical function, muscle strength, and global disease assessments. Future work will be needed to determine what constitutes a normal CMAS score in children of varying ages, particularly in younger children. The notion that older children have a greater reserve of muscle strength to lose before they will develop a detectable loss in physical function is unproven. Adam M. Huber MD*, Frederick W. Miller MD, PhD , Lisa G. Rider MD , * IWK Health Centre and Dalhousie University Halifax, Nova Scotia, Canada, National Institutes of Health Bethesda, MD.

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