Dr. Targoff has received consulting fees (more than $10,000) from the Oklahoma Medical Research Foundation Clinical Immunology Laboratory.
Clinical and Laboratory Features Distinguishing Juvenile Polymyositis and Muscular Dystrophy
Article first published online: 27 NOV 2013
Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Arthritis Care & Research
Volume 65, Issue 12, pages 1969–1975, December 2013
How to Cite
Mamyrova, G., Katz, J. D., Jones, R. V., Targoff, I. N., Lachenbruch, P. A., Jones, O. Y., Miller, F. W., Rider, L. G. and the Childhood Myositis Heterogeneity Collaborative Study Group (2013), Clinical and Laboratory Features Distinguishing Juvenile Polymyositis and Muscular Dystrophy. Arthritis Care Res, 65: 1969–1975. doi: 10.1002/acr.22088
- Issue published online: 27 NOV 2013
- Article first published online: 27 NOV 2013
- Accepted manuscript online: 7 AUG 2013 12:42PM EST
- Manuscript Accepted: 26 JUL 2013
- Manuscript Received: 23 FEB 2013
- Intramural Research Program of the NIH
- National Institute of Environmental Health Sciences. Grant Number: Project ES101074
- Cure JM Foundation
To differentiate juvenile polymyositis (PM) and muscular dystrophy, both of which may present with chronic muscle weakness and inflammation.
We studied 39 patients with probable or definite juvenile PM and 9 patients with muscular dystrophies who were initially misdiagnosed as having juvenile PM. Differences in demographic, clinical, and laboratory results; outcomes; and treatment responses were evaluated by Fisher's exact and rank sum tests. Random forests classification analysis and logistic regression were performed to examine significant differences in multivariable models.
Clinical features and serum muscle enzyme levels were similar between juvenile PM and dystrophy patients, except 89% of dystrophy patients had muscle atrophy compared with 46% of juvenile PM patients. Dystrophy patients had a longer delay to diagnosis (median 12 versus 4 months) and were less frequently hospitalized than juvenile PM patients (22% versus 74%). No dystrophy patients, but 54% of juvenile PM patients, had a myositis autoantibody. Dystrophy patients more frequently had myopathic features on muscle biopsy, including diffuse variation of myofiber size, fiber hypertrophy, and myofiber fibrosis (44–100% versus 8–53%). Juvenile PM patients more frequently had complex repetitive discharges on electromyography and a complete response to treatment with prednisone or other immunosuppressive agents than dystrophy patients (44% versus 0%). Random forests analysis revealed that the most important features in distinguishing juvenile PM from dystrophies were myositis autoantibodies, clinical muscle atrophy, and myofiber size variation on biopsy. Logistic regression confirmed muscle atrophy, myofiber fibrosis, and hospitalization as significant predictors.
Muscular dystrophy can present similarly to juvenile PM. Selected clinical and laboratory features are helpful in combination in distinguishing these conditions.