Inflammatory myopathy with cytochrome oxidase negative muscle fibers: methotrexate treatment.
Inflammatory myopathy with cytochrome oxidase negative muscle fibers (IM/COX-) is characterized by slowly progressive weakness, most prominent in the quadriceps, muscle fibers with reduced COX staining and mitochondrial DNA mutations, and a poor response to corticosteroid treatment. We reviewed records of quantitative measurements of muscle strength in 7 IM/COX- patients to evaluate the outcomes after treatment with oral, once weekly, methotrexate for an average of 15 months. We compared the results to 6 patients with IM/COX- who received no long-term immunosuppression, and to 4 with inclusion body myositis (IBM) who received methotrexate during the same period. Methotrexate treatment of IM/ COX- was followed by improved muscle strength in 5 of 7 patients, averaging 17+/-5%. In contrast, there was no improvement in the strength of 6 untreated IM/COX- patients (-6+/-4%; P=0.003), or 4 methotrexate-treated IBM patients (1+/-2%; P=0.03). We conclude that, despite clinical similarities to inclusion body myositis, which is usually refractory to immunosuppressive therapy, strength in IM/COX- appears to improve with methotrexate treatment. Biopsy studies of inflammatory myopathies with evaluation of muscle for mitochondrial changes and vacuoles can help to direct the choice of appropriate immunomodulating treatments.
Levine
T D
TD
Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Pestronk
A
A
D000368:Aged; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use*; D008297:Male; D008727:Methotrexate / Q000627:therapeutic use*; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000503:physiopathology; D009220:Myositis / Q000188:drug therapy* / Q000201:enzymology* / Q000503:physiopathology; D018979:Myositis, Inclusion Body / Q000188:drug therapy / Q000503:physiopathology; D016896:Treatment Outcome
D007166:Immunosuppressive Agents; D003576:Electron Transport Complex IV; D008727:Methotrexate