VP.43 Immune-mediated necrotizing myopathies: clinical-serological features of a large Italian cohort of patients

Abstract

Immune-mediated necrotizing myopathies (IMNMs) represent a heterogeneous group of muscle disorders recently identified within the spectrum of idiopathic inflammatory myopathies (IIMs) by distinctive clinical, pathological, serological, and therapeutic features. Currently, three different IMNM entities have been defined: 1) anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) myopathy; 2) anti-signal recognition particle (SRP) myopathy; 3) antibody negative IMNM. An accurate diagnosis of IMNMs is relevant for prognostic purposes and to provide the best chance of treatment for patient subtypes and prevent long-term disability. We aimed to investigate clinical and histological features of different serological subgroups within an Italian cohort of IMNM patients. We included 128 patients diagnosed with IMNM in 12 neuromuscular referral centers in Italy, relying on the 2017 European Neuromuscular Centre criteria. The study population was composed by 57 males and 71 females, with an overlapping median age at disease onset equal to 65 years old for men and 64 for women. Forty-five patients (35,2%) were positive for HMGCR autoantibodies (Abs), of whom 30 had a history of statin exposure (13 males, 17 females). Among anti-HMGCR Ab–positive IMNM patients naïve to statin therapy, females were more represented (61,5%). Furthermore, 35 patients (27,3%) had anti-signal recognition particle (SRP) Abs, 27 patients (21,1%) resulted seronegative, and 21 patients (16,4%) did not have a complete Ab assessment. Malignancies were reported in 17 patients. Onset muscle weakness distribution, muscle biopsy pathological features, clinical outcome after therapy, CPK levels and extra-muscular manifestations according to serological type were evaluated. This study provides new insights about IMNM characteristics in a large Italian cohort.