Increasing evidence suggests common genetic associations across a variety of autoimmune disorders, reflecting genuine susceptibility effects.1 Shadaskhari and colleagues (ACR 2013: Abstract 575) assessed whether there are overlaps in prevalence between systemic lupus erythematosus (SLE) and other rheumatologic autoimmune diseases, specifically psoriasis and psoriatic arthritis, and whether patients with SLE who have multiple autoimmune disorders represent a distinct clinical entity.
The authors examined the prevalence of psoriasis and psoriatic arthritis in 445 patients with SLE based on the history, physical examination, laboratory measures, and radiological studies. A diagnosis of psoriasis was made by a dermatologist or a rheumatologist, and the diagnosis of psoriatic arthritis was made on the basis of the Classification Criteria for Psoriatic Arthritis (CASPAR).2 The diagnosis of SLE was based on American College of Rheumatology criteria.3 Among 445 patients with SLE, 23 (5.1%) were diagnosed as having psoriasis, of which 20 (4.5%) were found to have psoriatic arthritis. These percentages are significantly higher than the prevalence of psoriasis and psoriatic arthritis in the general population, which have been reported to be approximately 2%.4
These results indicate that the prevalence of psoriatic arthritis in patients with SLE is significantly higher than that found in the general population (P <.0001). The prevalence of common clinical indicia of SLE—malar rash, discoid rash, photosensitivity, and arthritis—were increased in patients with SLE and concomitant psoriatic arthritis, whereas antiphospholipid antibodies were less common in these patients compared with patients who have SLE and no concurrent psoriatic arthritis. There was no significant association of psoriatic arthritis in patients with SLE who had other clinical signs and symptoms of SLE, including seizures, psychosis, oral ulcers, serositis, proteinuria, anemia, leukopenia, thrombocytopenia, hemolytic anemia, or anti-Sm or anti-DNA antibodies.
Although the authors concluded that psoriatic arthritis has an increased prevalence in patients with SLE, and that patients with overlapping disorders may represent a distinct clinical entity within SLE, these data also lend further support to the increasing body of evidence suggesting a common, genetically determined pathophysiology among autoimmune disorders. Moreover, this unique subgroup of patients with concomitant SLE and psoriatic arthritis pose significant diagnostic and therapeutic challenges. For example, the diagnosis of SLE versus psoriatic arthritis in patients presenting with polyarthritis and overlapping clinical indicia is difficult. Similarly, the management of patients with concurrent SLE and psoriatic arthritis is a challenge, because therapies that are used for one disorder may worsen the other (eg, hydroxychloroquine for SLE may worsen symptoms of psoriatic arthritis, and TNF antagonists that are used in treating psoriatic arthritis have been known to cause or worsen lupus-like symptoms).
References
1. The Wellcome Trust Care Control Consortium. Nature. 2007;447:661-678.
2. Taylor W, et al. Arthritis Rheum. 2006;54:2665-2673.
3. Hochberg MC. Arthritis Rheum. 1997;40:1725.
4. Ruiz DG, et al. Rev Bras Reumatol. 2012;58:630-638.
5. Goldenstein-Schainberg C, et al. Rev Bras Reumatol. 2012;52:98-106.