Steroid-responsive myopathy: immune-mediated necrotizing myopathy or polymyositis without inflammation?

To describe the clinical course and steroid responsiveness of a patient with subacute proximal symmetric weakness, very high serum creatine kinase activity, and myopathic pattern with fibrillations in the electromyogram, whose muscle biopsy showed necrotizing myopathy, with practically no inflammation.

Case report.

Academic research.

Diagnosis of muscular dystrophy was suggested; nevertheless, steroid treatment was initiated, and the patient recovered and gained normal strength. However, after a few years he stopped treatment, and all symptoms recurred. He developed severe proximal weakness of all limbs. Another biopsy showed similar findings, with no inflammation; still, he responded favorably to steroids and immunosuppressive medications. Currently on a low dose of prednisone and methotrexate, he has no neurological deficit.

The absence of inflammation in muscle biopsy may lead to misdiagnosis of muscular dystrophy; however, if the clinical impression is that of inflammatory myopathy, an immunomodulatory treatment should be initiated. During the past century, there has been much controversy about the diagnosis of polymyositis (PM). The debate is still ongoing. We present hereby a patient with typical course and clinical features of PM who underwent two muscle biopsies, several years apart, which showed necrotizing myopathy, practically without inflammation, leading to misdiagnosis of muscular dystrophy. This report brings up the dispute regarding the role of muscle biopsy in the diagnosis of PM.