Clinical and laboratory features of overlap syndromes of idiopathic inflammatory myopathies associated with systemic lupus erythematosus, systemic sclerosis, or rheumatoid arthritis.

Because overlap syndromes (OSs) are rarely described, we analyzed retrospectively their frequencies and correlations in Brazilian series of 31 patients with dermatomyositis (DM)/polymyositis (PM) associated with systemic lupus erythematosus (SLE), systemic sclerosis (SSc), or rheumatoid arthritis (RA) attended at a referral single center. Myositis-specific autoantibodies (MSAs: anti-Jo-1, anti-PL-7, anti-PL-12, anti-EJ, anti-OJ, anti-SRP, anti-Mi-2) and myositis-associated autoantibodies (MAAs: anti-PM-Scl75, anti-PM-Scl100, anti-Ku) as well as specific autoantibodies related to SLE, SSc, and RA were investigated. The mean age of the OS patients (9 DM and 22 PM) was 44.6 ± 15.4 years, with a predominance of women (83.9 %) and white ethnicity (58.1 %). PM was the most frequent inflammatory myopathy, and the clinical presentation of DM/PM was significantly different among the OS groups. Overlap was found with SSc (48.4 %), SLE (29.0 %), and RA (22.6 %). The clinical manifestations of DM/PM were identified simultaneously with SSc and RA in the majority of cases, in contrast to identification in the SLE group (p < 0.05). All patients were positive for antinuclear antibodies, and the prevalence of MSA and MAA was 38.8 % in all OS groups, mutually exclusive, and more frequent in the SSc group. Comparing the clinical and laboratory features, there was a higher frequency of vascular (skin ulcers, Raynaud's phenomenon) and pulmonary (interstitial lung disease) involvement in the SSc group (p < 0.05). Moreover, there were no differences among the groups in relation to disease relapse and deaths. Concluding, this is the first study to show the different characteristics of a series of patients with connective tissue disease (CTD)-OS in the heterogeneous Brazilian population.