Background: Idiopathic inflammatory myopathies (IIM) are characterised by chronic muscle inflammation, various organ involvements and the presence of certain specific autoantibodies.
Objectives: We assessed survival and characterized subsets based on muscle biopsy and myositis specific autoantibodies (MSAs).
Methods: Eighty-two patients with muscle biopsy proven IIM were included in the study. All cases had MSA and myositis associated antibody (MAA) tests (Jo-1, PL-7, PL-12, Mi-2, SRP, Pm-Scl, Ku, ribosomal, AMA-M2) using Western-blot kits. Survival analysis was performed by Kaplan Meier test.
Results: Fift y-nine women and 23 men with a mean age of 49.3 ± 14.6 years and with 7.5 ± 4.5 years of mean
follow-up time were included. Interstitial lung disease (ILD) (51.2%), arthritis (51.2%), Raynaud’s phenomenon
(42.7%), skin symptoms (45.1%), dysphagia (24.4%) and significant cardiac involvement (15.9%) were the most prevalent disease manifestations. 15 cases were associated with malignancies. Myositis subsets were as follow: 26.8% (n=22) polymyositis /PM/, 30.5% (n=25) dermatomyositis/DM/, 1.2% (n=1) juvenile PM/DM, 8.5% (n=7) inclusion body myositis /IBM/, 22% (n=18) overlap myositis /OM/, and 11% (n=9) immune mediated necrotizing myopathy /IMNM/. Malignancy was most frequently associated with IMNM (7 out of 9 patients). Altogether 18 patients died from which 15 deaths can be connected to myositis related events. Eight patients died of malignancies, 5 patients due to cardiac events (heart failure, arrythmia), 2 due to lung fibrosis and 3 by unknown causes. The worst prognosis with a 10-year survival of 31 % was in the IMNM subgroup (p<0.01), followed by patients with PM (68%), IBM (84%) OM (85.1%) and DM (85.3%). Mi-2 positive patients had a favourable prognosis with a 10-year survival of 100%. Patients with IMNM had the worst prognosis (10-year survival of 31.1%), followed by PM (76%), DM and IBM (85.7% each). Patients with antisynthetase antibody-positivity had worse prognosis compared to patients with other antibodies or no identifiable antibodies (10-year survival of 55%, n=16) (p<0.05).
Conclusions: Th e worst survivals were seen in the IMNM and PM groups, due to the high frequency of the underlying malignancies and cardiac manifestations. Although ILD was the most frequent involvement, it was not the main cause of death
