Prevalence of monoclonal gammopathy among patients with psoriatic arthritis

The occurrence of monoclonal gammopathy is common in chronic inflammatory disorders such as chronic infections and autoimmune disorders. There is limited information about the prevalence of monoclonal gammopathy in psoriatic arthritis (PsA). We investigated the prevalence, type, and associated features of monoclonal gammopathy in patients with PsA.

We performed a cross-sectional analysis of patients followed from 2008 to 2011 at the University of Toronto PsA clinic. The presence of monoclonal gammopathy was defined as the occurrence of a discrete band in the gammaglobulin region on at least 2 separate serum protein electrophoresis tests performed 6 months apart. Comparisons between patients with and those without monoclonal gammopathy were performed using t tests for continuous variables and chi-square tests for categorical variables.

Of the 361 patients with PsA, 35 (9.7%) had evidence of monoclonal gammopathy in at least 2 separate blood tests. Seven (24%) of the 29 patients who were tested for Bence Jones protein were found to be positive. One patient was diagnosed as having multiple myeloma. Patients with monoclonal gammopathy were older (p = 0.001), had a longer duration of psoriasis (p = 0.02) and PsA (p = 0.006), were less likely to use disease-modifying antirheumatic drugs (p = 0.05), and had higher sedimentation rate (p = 0.01) and lower hemoglobin levels (p = 0.02). Patients with monoclonal gammopathy also trended toward having more active disease, with a higher active joint count (p = 0.07).

Monoclonal gammopathy occurs in patients with PsA more commonly than in the general population. Its prevalence is associated with measures of disease activity and duration.