Differentiating Necrotizing Myositis from Polymyositis
April 1, 2012 3 minutes read
Differentiating Necrotizing Myositis from Polymyositis
Abstract & Commentary
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Necrotizing myositis is a newly described inflammatory myopathy that has an autoimmune etiology and may be associated with anti-signal recognition particle autoantibodies.
Source: Ellis E, et al. Necrotizing myopathy: Clinicoserologic associations. Muscle Nerve 2012;45:189-194.
Necrotizing myopathy (NM) lacks the mononuclear inflammatory cell infiltrates seen histologically on muscle biopsy in idiopathic inflammatory myopathy (IIM), including polymyositis, dermatomyositis, and inclusion body myositis. Both groups, however, present with proximal weakness, elevated serum creatine kinase levels, and similar electromyographic abnormalities comprising positive waves, fibrillation potentials, and small amplitude, short duration, myopathic motor unit potentials. Are there particular clinical and serological features or comorbidities associated with NM that set it apart from IIM?
All muscle histopathology reports from 1992-2009, from the Neuropathology Laboratory, Institute of Medical and Veterinary Science, Adelaide, South Australia, were reviewed to identify cases of NM. Record review of their clinical features, including symptoms, signs, and comorbidities, was then compared to those of patients with histologically confirmed IIM, based on Hohlfeld criteria. Statistical analysis comprised Fisher's exact two-tailed test and the chi square test, with significance set at P < 0.05.
Among 86 patients initially identified as NM, 64 were confirmed (based on review of biopsy specimens), demonstrating muscle fiber necrosis, macrophage myophagia, and basophilic fiber regeneration in the absence of lymphocytic infiltrates, infrequent immunostain positivity for CD45 lymphocytes or CD68 mononuclear cells. Only 15% demonstrated major histocompatibility complex (MHC) class I and II up-regulation, a feature usually seen with IIM. Males comprised 61% of the cases (39/64), significantly higher than the female predominance seen in IIM (P = 0.0004), and myalgia was more frequent in NM than IIM, 81% vs 41% (P = 0.0005). Distal weakness was not seen in any NM patient, compared to 27% of the IIM group. Among various comorbidities, including hypertension, diabetes mellitus, thyroid disease, cerebrovascular or ischemic cardiovascular disease, only systemic lupus erythematosus was found to be significantly more common in NM compared to IIM (21% vs 1%, P = 0.004), but hypertension and diabetes mellitus were found in 65% and 23% of NM cases, respectively. Anti-signal recognition particle (anti-SRP) antibodies, reportedly a marker for NM, were not found in any patient, but anti-PMScl75, anti-Ro-52, anti-anti-Ku were found in 5, 2, and 1 patients, respectively. No association with malignancy was detected in this cohort of NM. Comprehensive cardiovascular evaluation is warranted in patients diagnosed with NM.
Commentary
NM appears to be a newly emerging, immune-mediated myopathy, associated with the presence of anti-SRP autoantibodies, statins, malignancy, and viral infection.1 Clinically similar to polymyositis, it has been differentiated histologically based on the presence of profound muscle fiber necrosis, regeneration, and an absence of inflammatory cells. Response to immunosuppressive therapy may be good, and includes a prolonged course of high-dose oral prednisone, followed, where necessary, by steroid-sparing agents such as mycophenolate mofetil, methotrexate, azathioprine, intravenous immunoglobulin, or plasma exchange. One case of paraneoplastic NM responded to cetuximab, an anti-epidermal growth factor receptor monoclonal antibody. The role of anti-SRP autoantibodies in NM remains uncertain, but their levels appear to correlate with disease activity, suggesting that they may both play a role in pathogenesis and be a useful marker in monitoring patients undergoing treatment.
Reference
1. Liang C, Needham M. Necrotizing autoimmune myopathy. Curr Opin Rheumatol 2011;23:612-619.
Necrotizing myositis is a newly described inflammatory myopathy that has an autoimmune etiology and may be associated with anti-signal recognition particle autoantibodies.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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