Causes of psoriasis are still unknown, so the subsequent development of psoriatic arthritis is poorly understood as well. Researchers believe that genetic, environmental, and immunologic factors all contribute to development of the disease as follows:

  • Genetics. Support for genetic and environmental hypotheses has been generated through studies of families, specifically identical twins. One study found that if one twin develops psoriasis, 70% of the time the other twin would develop it as well.4 The 30% discrepancy suggests that outside environmental factors are also at work. Studies have shown that patients with close relatives with psoriasis have more than a 40% risk of developing psoriatic arthritis.5
  • Environmental. Nothing has been proven to suggest a specific environmental factor is to blame, although researchers believe infectious agents such as Streptococci and Staphylococci, as well as physical trauma, are the most likely culprits. Psoriasis can appear where there is skin trauma. In some patients, arthritis can develop in an injured joint.
  • Immunologic. Psoriatic arthritis has been known to occur in patients with immune system abnormalities as well as human immunodeficiency virus (HIV).

Having a risk factor for psoriasis does not guarantee that psoriatic arthritis will develop.

References:

  1. Krueger G, Ellis CN. "Psoriasis--recent advances in understanding its pathogenesis and treatment," Journal of the American Acadamy of Dermatology. 53 (1 Suppl 1): S94–100 (2005).
  2. Karason A, Love TJ, Gudbjornsson B. "A strong heritability of psoriatic arthritis over four generations — the Reykjavik Psoriatic Arthritis Study," Rheumatology (Oxford) 48(11):1424-1428, 2009
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Written by Judith Frank, MD
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