Compared with patients with systemic sclerosis (SSc), patients with SSc-systemic lupus erythematosus (SLE) overlap syndrome were significantly younger at diagnosis, had higher rates of pulmonary arterial hypertension (PAH), and less frequently had SSc cutaneous manifestations, according to findings published in The Journal of Rheumatology.

The prevalence of SSc-SLE overlap syndrome ranges from 8.4% to 14.7%, but there is relatively little information in the literature about its clinical or epidemiologic characteristics. Investigators sought to fill this knowledge gap by better defining SSc-SLE in terms of prevalence, SSc characteristics, and survival.

A total of 1252 patients from the Toronto Scleroderma Program were enrolled between 1970 and 2017, including 1166 patients with SSc and 86 diagnosed with SSc-SLE. The primary end point was median survival time between diagnosis and mortality from any cause, and secondary end points included various demographic, clinical, and serologic disease characteristics.

The prevalence of SSc-SLE was 6.8%. These patients had longer median survival times compared with those with SSc only (26.1 vs 22.4 years), although the difference was not significant (log-rank P =.06). When adjusted for diffuse subtype and female sex, between-group survival differences were attenuated (hazard ratio, 1.07; 95% CI, 0.67-1.67). Participants with SSc-SLE also tended to be younger at diagnosis compared with patients with SSc (37.9 vs 47.9 years; P <.001), and more often of East Asian (20% vs 5.5%) or South Asian (12% vs 5.1%) descent, with a higher proportion of women (92% vs 81%; P =.02).

Patients with SSc-SLE more frequently had lupus anticoagulant (6% vs 0.3%; standardized mean difference [SMD], 32%; P <.001), anticardiolipin antibody positivity (6% vs 0.9%; SMD, 27%; P <.001), and PAH (52% vs 31%; SMD, 44%; P <.001). However, compared with patients with SSc, individuals with SSc-SLE had lower rates of diffuse subtype (12% vs 35%; P <.001), calcinosis (13% vs 27%; SMD, 35%; P =.007), and telangiectasia (49% vs 75%; SMD, 56%; P <.001). Differences between SSc-SLE and SSc were equivocal or not significant for renal crisis (7% vs 7%; SMD, 2%), digital ulcers (38% vs 32%; SMD, 12%), and interstitial lung disease (41% vs 34%; SMD, 14%).

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Study strengths included a large sample size, extended follow-up, and thorough mortality data. Study limitations included a potentially conservative prevalence estimate, possible survival bias, low proportion of SSc antibody positivity, and possible artificially high PAH prevalence.

The authors observed, “It appears that having an overlap with SLE does not confer either an increased risk or protective effect for mortality.” They recommended that all patients with SSc-SLE be carefully monitored for development of digital ulcers, interstitial lung disease, and renal crisis as part of their routine management.

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Reference

Alharbi S, Ahmad Z, Bookman AA, et al. Epidemiology and survival of systemic sclerosis-systemic lupus erythematosus overlap syndrome [published online July 15, 2018]. J Rheumatol. doi:10.3899/jrheum.170953