Intravenous human immunoglobulin and/or methylprednisolone pulse therapies as a possible treat-to-target strategy in immune-mediated necrotizing myopathies

To evaluate the relevance of immunoglobulin (IVIg) and/or methylprednisolone pulse therapies in immune-mediated necrotizing myopathy (IMNM). Secondarily, to analyze the muscle damage measured by late magnetic resonance images (MRI). This retrospective study included 13 patients with defined IMNM (nine patients positive for the anti-signal recognition particle and four patients positive for hydroxyl-methyl-glutaryl coenzyme A reductase) who were followed from 2012 to 2018. International Myositis Assessment and Clinical Studies Group (IMACS) scoring assessed the response to a standardized treat-to-target protocol with disease activity core-set measures and late magnetic resonance imaging (MRI). The patients had a mean age of 53.5 years and were predominantly female and of white ethnicity. Median symptom and mean follow-up durations were 4 and 39 months, respectively. All patients received IVIg and/or methylprednisolone pulse therapies. All IMACS core-set measurements improved significantly after initial treatment. Nine patients achieved complete clinical response and among them 2 had complete remission. Eleven patients had discontinued glucocorticoid use by the end of the study. Only 2 patients had moderate muscle atrophy or fat replacement observed by MRI, with the remainder presenting normal or mild findings. Our patients with IMNM treated with an aggressive immunosuppressant therapy had a marked improvement in all IMACS core-set domains. Moreover, the MRI findings suggest that an early treat-to-target approach could reduce the odds of long-term muscle disability. Methylprednisolone and/or IVIg pulse therapies aiming at a target of complete clinical response are potential treatment strategies for IMNM that should be studied in future prospective studies.