Psoriatic Arthritis

by Grant Louie, M.D., M.H.S.

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis in the setting of skin or nail psoriasis. It encompasses a heterogenous group of arthritides, ranging from a peripheral symmetric polyarthritis sometimes clinically indistinguishable from rheumatoid arthritis (RA) to an asymmetric oligoarthritis of mostly the lower extremities to an axial spondyloarthritis with enthesitis and dactylitis.  The latter clinical presentation explains the frequent classification of PsA in the group of rheumatic diseases known as the seronegative spondyloarthropathies.

*Images within this article are from the American College of Rheumatology Slide Collection.


The incidence of PsA in the United States is estimated to be 6-7 per 100,000 per year.  The prevalence of PsA is approximately 0.04-0.1% of the U.S. adult population.  PsA occurs in 20-30% (range 6-42%) of patients with psoriasis.  Peak incidence occurs at ages 30-55 years, and both sexes are equally affected.  PsA usually develops concurrently or within 7 years of onset of psoriasis, although 15-20% of patients with PsA will present before development of psoriasis.


The precise etiology of PsA remains elusive, though heritability, infection, and physical trauma are frequently cited potential causes. Major histocompatibility alleles HLA-B27, -B7, -B13, -B17, -B57, and –Cw*0602 have been discovered to be associated with PsA in genetic susceptibility studies.  Genome wide association studies (GWAS) of patients with psoriasis and PsA have recently identified other susceptibility loci, including IL23A, IL23R, IL12B, TNFAIP3, TNIP1, IL4, IL13, and TRAF3IP2.  Group A streptococcus has been associated with development of guttate psoriasis, and ribosomal RNA of this bacterium has been detected in peripheral blood and synovial fluid of patients with PsA.  HIV is associated with the development of psoriasis and PsA.  Physical trauma, the so-called Koebner phenomenon, has been reported to induce the onset of psoriasis.


The severity of arthritis at the time of presentation of PsA and the subsequent disease course may be correlated.  Polyarthritis in the presence of elevated acute phase reactants, radiographic evidence of joint erosions, and inadequate response to initial pharmacotherapy predict a more severe disease course.  As seen in RA, PsA can significantly impact physical functioning and health-related quality of life.  Without prompt therapeutic  intervention, joint destruction may occur rapidly.

Other factors that are associated with a worse prognosis include extensive cutaneous involvement, young age at disease onset, and a strong family history of psoriasis.


  1. Mease PJ.  Psoriatic arthritis: update on pathophysiology, assessment and management. Ann Rheum Dis 2011;70(Suppl 1):i77-84.
  2. Castelino M, Barton A. Genetic susceptibility factors for psoriatic arthritis. Curr Opin Rheumatol 2010;22(2):152-15
  3. Gottlieb A, Menter A, Mendelsohn A, Shen YK, Li S, Guzzo C, et al. Ustekinumab, a human interleukin 12/23 monoclonal antibody, for psoriatic arthritis: randomised, double-blind, placebo-controlled, crossover trial. Lancet 2009;373(9664):633-640.
  4. Mease PJ. Psoriatic arthritis assessment and treatment update. Curr Opin Rheumatol 2009;21(4):348-355.
  5. Ritchlin CT, Kavanaugh A, Gladman DD, Mease PJ, Helliwell P, Boehncke WH, et al. Treatment recommendations for psoriatic arthritis. Ann Rheum Dis 2009;68(9):1387-1394.
  6. Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P, Mielants H, CASPAR Study Group. Classification criteria for psoriatic arthritis: development of new criteria from a large international study. Arthritis Rheum 2006;54(8):2665-2673.

*Images within this article are from the American College of Rheumatology Slide Collection.

Updated: October 3, 2012

Grant Louie, M.D., M.H.S.

About Grant Louie, M.D., M.H.S.

Assistant Professor of Medicine
Johns Hopkins University