Background Monoclonal gammapathy of undetermined significance (MGUS) is premalignant plasma-cell disorder. Its prevalence is about 3.2% of the general population older than 50 years. In patients with rheumatoid Arthritis (RA), little is known about the prevalence of MGUS and its evolution under biologics.

Objectives To assess the prevalence of MGUS in longstanding RA, the characteristics of patients with MGUS, and the evolution of MGUS under abatacept.

Methods ORA (Orencia and Rheumatoid arthritis) is a French prospective 7-year registry which included 1017 RA patients at abatacept initiation. Data on disease characteristics, biologic abnormalities including the presence of a monoclonal gammapathy, and the occurrence of severe adverse events, including cancers such as lymphomas, myelomas are collected at enrollment and every 6 months.

Results Among the 1017 RA patients included in ORA registry, 38 had a MGUS (3.7%). Baseline disease characteristics (gender, age, RA duration, positivity for anti-CCP and rheumatoid factors, DAS28ESR) were not significantly different between patients with or without MGUS.

In RA patients with MGUS, mean age and RA duration were 58.2±13.6 and 13.8±9.5 years, respectively. 76.3% were women 52.6% and 55.2% had anti-cyclic citrullinated peptide (anti-CCP) and rheumatoid factors (RF), respectively. 92.1% of patients previously received biological treatments (with a mean of 2.5±1.3 biologics): 89.5% previously received anti-TNFs and 42.1% receive rituximab As concomitant treatment, 47.3% received methotrexate and 84.2% corticosteroids.

During the follow-up of 1.50±1.10 years, no significant change in the blood level of the monoclonal component was observed. Two patients developed a multiple myeloma;. For the first patient, Immunoglobulin G Kappa stade 3 myeloma was diagnosed only 83 days after abatacept initiation. For the second patient, immunoglobuline G myeloma stade 1 was diagnosed 1 year after abatacept initiation. No lymphoma nor amyloidosis occurred.

Conclusions The prevalence of MGUS in this population with longstanding RA was similar to that observed in the general population (∼3%). No significant effect of abatacept on the blood level of the monoclonal component was observed after 2 years of prospective follow-up. Although no signal has been observed, a longer follow-up is needed to evaluate the effect of abatacept on the risk of malignant transformation of MGUS.

References

1. Kyle RA et al. Prevalence of MGUS, N Engl J Med 2006;354:1362-9.

2. Smale SW et al. Scand J Rheumatol. 2007;36: 405-6.

Disclosure of Interest None declared