Background Autoimmune myositis (AIM) is a syndrome characterized by proximal muscle weakness, involvement of the cellular and humoral immune systems in skeletal muscle pathology, and presence of autoantibodies (Abs) (myositis-specific (MSAs) and myositis-associated (MAAs)) in the serum of some patients.¹ Myositis Abs are collectively referred to overlap Abs. Although it has been suggested that myositis Abs may identified distinct disease entities, in practice these Abs often segregate with different overlap clinical manifestations. The discovery of myositis Abs and association with different clinical features lead to create a Troyanov's classification, complemented the original Bohan&Peter classification. The original Bohan and Peter classification should be abandoned as it leads to misclassification of patients. Much of myosites are composed of ovelap myositis (OM).² The question is: Which classification to use - Troyanov's classification or a new approach?

Objectives The objectives of the study were to analyze association between overlap Abs and different clinical manifestations, to compare Bohan&Peter's classification and Troyanov classification, and to determine the most common myostis in a group of patients with AIM in Bulgarian population.

Methods We collected sera from 93 patients with myositis in the prospective study. The diagnosis was determined using Bohan and Peter classification and Troyanov's classification. Sera were tested by Immunoblot test and enzyme linked immunosorbent assay. Association between clinical features and Abs were analyzed by Chi-square analysis, Fisher's exact test. Positive predictive value (PPV) and negative predictive value (NPV), and likelihood ratio (LR) were calculated using SPSS 13.0 for Windows. The frequency comparisons among groups were analyse by Chi-square method.

Results Overlap Abs (MSAa and MAAs) were expressed in 70% of patients with AIM. It was found that the presence of overlap Abs was strongly associated with overlap clinical features at AIM diagnosis, respectively it was determined specifity 75%, PPV 89.5%, positive LR 3.37. The sensitivity of Abs for overlap features was 84%, as NPV was 65%. Polymyositis was the most common AIM according to the classification Bohan&Peter, accounting for 32% of the patients at diagnosis, whereas its frequency fell to 11.25% with Troyanov clinicoserologic classification. The frequency of myositis associated with other connective tissue diseases was 30% according to the original classification, when using clincoserelogic classification the frequency of overlap myositis was 70%. In the study, systemic lupus erythematodes was the most common connective tissue disease associated with myositis, in 34.3% of patients with overlap myositis.

Conclusions It has been suggested that much of AIM aren't an independent nosologic entity. They are composed of overlap myositis. It is necessary to use a novel approach to the classification of AIM, approach, which based on the clinical features and immunological profile of the patients.

References

1. Nagaraju K, et al. Inflammatory muscle diseases: etiology and pathogenesis. In Rheumatology, Elsevier, Canada; 2011:1523-1535.

2. Troyanov Y., et al. Novel classification of idiopathic inflammatory myopathies based on overlap syndrome features and autoantibodies. Medecine, 2005, 84:231-249.

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.1921