Prevalence of monoclonal gammopathy of undetermined significance (MGUS) in systemic sclerosis: report from two italian centers

Background: Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic premalignant clonal plasma cell disorder. It is defined by the presence of serum levels of a monoclonal paraprotein lower than 3 g/dl, and a clonal plasma cell infiltration of the bone marrow less than 10%, in the absence of end-organ damage related to the lymphoproliferative process (1). The prevalence of MGUS in patients with chronic inflammatory and autoimmune disorders, commonly associated to an immune system impairment, has been found to be similar to that found in otherwise healthy individuals over the age of 50 (2,3). Objectives: To assess the prevalence of MGUS in a cohort of systemic sclerosis (SSc) patients from two Italian centers. Methods: Two-hundred-thirty-six SSc patients consecutively enrolled at the Rheumatology Unit of Naples and at the Division of Rheumatology of Milan from 2008 to 2011 were investigated. MGUS was suspected in case of the incidental finding of a monoclonal band in the gammaglobulin region at serum protein gel electrophoresis in two different tests taken 6 to 1 year apart. Patients with present or past diagnosis of a lymphoproliferative disorder/whatever malignancy were excluded from the analysis. Selected patients underwent further investigation to confirm and stage MGUS (bone marrow biopsy, etc). Results: Five out of 236 (2%) SSc patient (215 females and 21 males, aged 14-85 years, median 40.5), 39 (16.5%) patients with diffuse SSc, 189 (80%) with limited SSc, and 8 (3%) with SSc overlap syndrome had evidence of MGUS. One out of 236 SSc patients, with limited disease, had multiple myeloma; 24 patients out of 236 (10%) had polyclonal hypergammaglobulinemia but had no evidence of either MGUS or any other hematological disorders. The occurrence of MGUS was not associated to SSc features such as disease duration, severity or activity. Conclusions: To our knowledge, this is the first large cohort report on the prevalence of MGUS and its associations with SSc. Our data show that SSc patients have an MGUS prevalence similar to the the general population under the age of 60 (4-5). Two previous case series (6,7) are in line with our findings. In addition, we did not find any possible association with clinical features, in particular with disease duration, activity, severity, and medications. We concluded that SSc is not likely to be associated with pre-malignant clonal plasma cell disorders, although prospective studies are needed to confirm this hypothesis. References: Hillengass J, Moehler T, Hundemer M. Recent Results Cancer Res 2011;183:113-31. Gravitz L. Nature 480: S36-S37 Graber C. Nature 480: S54-S55 Crawford J, Eye MK, Cohen HJ. Am J Med 1987;82:39-45. Kyle RA, Therneau TM, Rajkumar SV, Larson DR, Plevak MF, Offord JR, et al. N Engl J Med 2006;354:1362-9. Morris Brown L. et al. Blood 2008;111:3388-3394 Broggini M et al. Rec Prog Med 1990; 81(5):306-309