FRI0449 Overlap myositis and primary myositis: clinical outcomes and prognosis

Background Among the subtypes of idiopathic inflammatory myopathy (IIM), it has been recognised that primary polymyositis (PM) and primary dermatomyositis (DM) have a worse prognosis than overlap syndrome (OM). However, the benign course of OM has not been confirmed in other studies. The identification of specific characteristics that could allow a correct classification may be important for its prognosis. Objectives To analyse clinical characteristics and survival of patients diagnosed with OM, and to compare if there are differences with other IIM subgroups in a multicentric cohort. Methods Retrospective, multicentric longitudinal observational study of a cohort of patients followed between January 1980 and December 2014, with a diagnosis of MII. The patients were divided into 2 groups: OM and primary idiopathic inflammatory myositis (PIIM), which included PM and DM. Patients classified as OM had to meet IIM criteria and criteria for rheumatoid arthritis (RA), systemic sclerosis (SSc), systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD) or primary Sjogren’s syndrome (SS). Results The present study included a total of 348 patients (98 OM, 250 PIIM). The connective tissue diseases associated with OM were: MCTD in 32 (32.7%), SSc in 29 (29.6%), SLE in 21 (21.4%), RA in 8 (8.2%) and SS in 8 (8.2%). Patients with OM showed remarkable differences compared to PIIM. In general, OM exhibited more extramuscular involvement and more complications, with more serious infections (41% vs. 24%, p Conclusions In the REMICAM registry of 348 inflammatory myopathies, 98 cases of myositis with overlap syndrome have been included, presenting with more extramuscular complications, more severe infections and higher mortality than other myopathies. It would be important to identify these patients at the onset of the disease, in order to closely monitor for development of possible complications. Disclosure of Interest None declared