Background/Purpose: Monoclonal gammopathy of undetermined significance (MGUS) is an asymptomatic premalignant clonal plasma disorder, defined by the presence of a serum monoclonal protein (M-protein) at a concentration < 30 g/L, a bone marrow (BM) plasma cell percentage < 10%, and absence signs and symptoms related to multiple myeloma (MM). The prevalence of MGUS in psoriatic arthritis (PsA) has been reported to be higher than the general population. However, no follow-up is available to determine whether these patients progress to MM.

Purpose

To determine the current prevalence of MGUS in the PsA cohort, evaluate the outcome of patients PsA – MGUS and determine any association of MGUS development and TNF inhibitors.

Methods: Included were patients followed at the PsA Clinic between January 2008 to January 2018. All patients fulfilled the CLASsification for Psoriatic Arthritis (CASPAR). MGUS was defined as the presence of a discrete band in the gamma- globulin region on at least 2 separate serum protein electrophoresis tests, performed 6 months apart. MM was the outcome of interest. Data extracted from our database included demographic variables, ESR level, use of conventional disease modifying antirheumatic drugs (cDMARD) and Biologic DMARDs (bDMARDs).  

Analyses included descriptive statistics [mean (SD) for continuous variables and frequency (percent) for categorical values]. Patients with MGUS were compared to those without using t -test, Wilcoxon test and Fisher test.

Results: Of the 883 patients assessed, 46 (5.3%) had evidence of MGUS on at least 2 separate blood tests. At the time of diagnosis 55.5% of patients were already on bDMARDs. Patients with MGUS had mean PsA duration of 14 years, were less likely to use DMARDs (30%), had more damage joints (24%), higher ESR levels (p=0.0001), but equal number of actively inflamed joints compared to the control group. 1 patient evolved to MM.  Both groups were similar in gender, race (Caucasian) and ages of PsA and PsO diagnosis.

Conclusion: The prevalence of MGUS among our cohort of patients with PsA was 5.2%, higher than the prevalence in whites (1.5% – 3%), but lower than the 9.7% reported by Eder et al.

Only 1 patient progressed and died of MM, less than that expected in the general population. The presence MGUS was associated with measures of disease activity/severity (higher ESR levels and more damaged joints). There was no relationship to bDMARDs.

Table 1.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/monoclonal-gammopathy-in-psoriatic-arthritis/