Necrotizing autoimmune myopathy (NAM) is a group of acquired myopathies characterized by prominent myofiber necrosis with little or no muscle inflammation. Recently, researchers identified autoantibodies (aAb) against 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) in patients with NAM, especially in statin-exposed patients. Here we report what is to our knowledge the first European cohort of patients with NAM.The serum of 206 patients with suspicion of NAM was tested for detection of anti-HMGCR aAb using an addressable laser bead immunoassay. Forty-five patients were found to be anti-HMGCR positive. Their mean age was 48.9 ± 21.9 years and the group was predominantly female (73.3%). Statin exposure was recorded in 44.4% of patients. Almost all patients had a muscular deficit (97.7%), frequently severe (Medical Research Council [MRC] 5 ≤3 in 75.5%). Subacute onset (<6 mo) was noted for most of them (64.4%). Nevertheless, 3 patients (6.6%) had a slowly progressive course over more than 10 years. Except for weight loss (20%), no extramuscular sign was observed. The mean CK level was high (6941 ± 8802 IU/L) and correlated with muscle strength evaluated by manual muscle testing (r = −0.37, p = 0.03). Similarly, anti-HMGCR aAb titers were correlated with muscular strength (r = −0.31; p = 0.03) and CK level (r = 0.45; p = 0.01). Mean duration of treatment was 34.1 ± 40.8 months, and by the end of the study no patient had been able to stop treatment.This study confirms the observation and description of anti-HMGCR aAb associated with NAM. The majority of patients were statin naive and needed prolonged treatments. Some patients had a dystrophic-like presentation. Anti-HMGR aAb titers correlated with CK levels and muscle strength, suggesting their pathogenic role.

Objective. Anti-signal recognition particle (anti-SRP) autoantibodies are associated with severe acquired necrotizing myopathies. The role of these autoantibodies remains elusive, and the evolution of anti-SRP levels over time is unknown. In this study, we developed an addressable laser bead immunoassay (ALBIA) technique to investigate a correlation between anti-SRP levels, serum creatine kinase (CK) levels, and muscle strength in patients with necrotizing myopathy.Methods. The diagnostic value of the ALBIA assay was determined by comparing serum levels of anti-SRP autoantibodies in 31 anti-SRP immunodotpositive patients to those in 190 healthy blood donors and 199 control patients with different inflammatory/ autoimmune conditions or polyclonal hypergammaglobulinemia. Among the 31 anti-SRP-positive patients, serum samples from 8 patients were monitored over time for levels of anti-SRP autoantibodies and levels of CK (determined at least 3 times, consecutively, over a mean followup period of 783 days). The relationship between levels of anti-SRP autoantibodies and levels of CK was tested using a linear mixed model.Results. The assay yielded positive results for anti-SRP in all anti-SRP immunodot-positive serum samples tested, while all control sera tested negative. The 8 anti-SRP-positive patients who were followed up longitudinally were found to have normalized CK levels and improved muscle strength. There was a striking correlation between the degree of myolysis, as measured by CK levels, in patients receiving therapy and the anti-SRP54 autoantibody levels in these same patients (P ‫؍‬ 0.002).Conclusion. Anti-SRP-positive myositis appears to be one of the few autoimmune diseases in which specific autoantibody levels are correlated with surrogate disease activity markers. These results reveal the usefulness of monitoring anti-SRP autoantibody levels in patients receiving therapy, and may also suggest a possible pathogenic role for anti-SRP autoantibodies in the necrotizing myopathies.Autoantibodies directed against signal recognition particles (anti-SRP) are present in a minority (4-6%) of patients with acquired inflammatory and/or necrotizing myopathies (1-5). Anti-SRP autoantibodies are generally associated with severe clinical forms of the disease, particularly those with heart and lung involvement (6,7) and resistance to steroid therapy (8-10).

Cancer can occur in patients with inflammatory myopathies. This association is mainly observed in dermatomyositis, and myositis-specific antibodies have allowed us to delineate patients at an increased risk. Malignancy is also reported in patients with necrotizing autoimmune myopathies, but the risk remains elusive. Anti-signal recognition particle or anti-HMGCR antibodies have been specifically associated with necrotizing autoimmune myopathies. We aimed at screening the incidence of cancer in necrotizing autoimmune myopathies. A group of patients (n = 115) with necrotizing autoimmune myopathies with or without myositis-specific antibodies was analysed. Malignancy occurred more frequently in seronegative necrotizing autoimmune myopathies patients and in HMGCR-positive patients compared to anti-signal recognition particle positive patients. Synchronous malignancy was diagnosed in 21.4% and 11.5% of cases, respectively, and incidence of cancer was higher compared to the general population in both groups. No specific type of cancer was predominant. Patients suffering from a synchronous cancer had a decreased median survival time. Cancer screening is necessary in seronegative necrotizing autoimmune myopathies and in HMGCR-positive patients but not in anti-signal recognition particle-positive patients.