Systemic sclerosis and prevalence of monoclonal immunoglobulin

Introduction: The purpose of this study was to estimate the prevalence of monoclonal immunoglobulin (MIg) among patients with systemic sclerosis (SSc) according to the capillary electrophoresis or immunofixation method of detection and to search for any related clinical correlations.

Patients and methods: Retrospective multicenter comparison of capillary electrophoresis and immunofixation results in SSc patients and of the characteristics of patients with and without MIg.

Results: The study included 244 SSc patients (216 women and 28 men, mean age: 55±14 years). Median time since SSc diagnosis was 51 months [0-320]; disease was diffuse in 48% of cases. Ten percent of patients had cancer, including Waldenström macroglobulinemia (n=1) and multiple myeloma (n=3). Capillary electrophoresis showed a γ-globulin anomaly in 41% of cases, and immunofixation in 18%: MIg (13.5%) and restriction of heterogeneity (4.5%). Capillary electrophoresis failed to detect 60% of the 33 MIg patients. Measurable MIg concentrations were obtained from 7 patients. MIg patients were significantly older at SSc diagnosis than those without MIg (p=0.002), had a lower diffusing capacity (p=0.002), a higher prevalence of pulmonary hypertension and cancer (p=0.002) and were more frequently positive for anti-mitochondrial and anti-beta2-glycoprotein-I antibodies (p=0.03 and p=0.02, respectively). Multivariate analyses showed that only age at test [hazard ratio 1.03 (95% CI, 1.00-1.07, p=0.04)] and presence of cancer [hazard ratio 4.46 (95% CI, 1.6-12.4, p=0.004)] were associated with MIg.

Conclusion: Immunofixation detected a high prevalence of MIg among SSc patients especially in patients aged 50-years or older. MIg was not detected by the standard capillary electrophoresis in 60% of cases and was significantly associated with cancer.