Psoriatic arthritis seems to be caused by a combination of genetic, environmental, health and lifestyle factors. Risk factors for psoriatic arthritis include:

Psoriasis
Having psoriasis is the biggest risk factor for developing psoriatic arthritis. People who have severe psoriasis are at an even greater risk of developing psoriatic arthritis than those who have mild psoriasis symptoms.1,2 Some researchers suggest that treating severe psoriasis can decrease the chances of developing psoriatic arthritis.2

Family history and genes
Studies have shown that patients with close relatives with psoriasis have more than a 40% risk of developing psoriatic arthritis.3 Several genes may contribute to psoriasis and psoriatic arthritis. For example, HLA-B08, HLA-B27, HLA-B38 and HLA-B39, are linked to psoriatic arthritis.4 Another gene, called HLA-C06, increases the risk of developing psoriasis but not psoriatic arthritis.

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Many people have the HLA-B genes listed above and never develop psoriasis or psoriatic arthritis. Likewise, a person who has none of those genes can still develop psoriatic arthritis.

Immune system abnormalities and HIV
Psoriatic arthritis has been known to occur in patients with immune system abnormalities as well as human immunodeficiency virus (HIV). A doctor may order an HIV test, particularly if the patient is a young adult who has new and severe symptoms.

Age
While people of any age can get psoriatic arthritis—including children—most people develop it in their 30s and 40s.

Smoking
Smoking increases the risk of developing psoriatic arthritis as well as many other autoimmune diseases.

Obesity
People who are overweight and obese have an increased risk of developing psoriatic arthritis, particularly if they already have psoriasis and/or genes that predispose them to psoriatic arthritis.

An imbalance of the gut microbiome (dysbiosis)
Microbes—bacteria and other microorganisms—live along the digestive tract. Normally, a person’s gut contains approximately 10,000 species of microbes. In general, the greater number of microbial species in the gut, the more resistant a person is to diseases.6 If the normal diversity of microbes decreases or becomes imbalanced, it is called dysbiosis. Dysbiosis increases the risk of developing psoriatic arthritis and other conditions, such as rheumatoid arthritis and irritable bowel disease.5,6

See Gut Microbiome Health and Diversity

Previous infection
People who are predisposed to psoriatic arthritis may notice symptoms appear shortly after getting a viral or bacterial infection. Psoriatic arthritis is an autoimmune disease, and the psoriatic arthritis may be triggered when the immune system actively fights off an infection.

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Physical trauma
In some patients, psoriatic arthritis develops develop in an injured joint. Trauma may trigger psoriatic arthritis similarly to infections: the injury occurs; the immune system is activated to facilitate healing; and psoriatic arthritis symptoms appear shortly afterwards.

Certain medical conditions
In addition to the above risk factors, psoriatic arthritis is associated with other medical conditions, such as cardiovascular diseases, chronic kidney disease, inflammation of the eyes (conjunctivitis and uveitis), mental health disorders, and certain metabolic disorders, such as type 2 diabetes.

Male or female sex does not seem to influence the risk of developing psoriatic arthritis (though it may influence their subtype). Having a risk factor for psoriasis does not guarantee that psoriatic arthritis will develop.

References:

  1. Ogdie A, Gelfand JM. Identification of risk factors for psoriatic arthritis: scientific opportunity meets clinical need. Arch Dermatol. 2010;146(7):785–788. doi:10.1001/archdermatol.2010.136. As cited in Ritchlin, CT, Colbert, RA, and Gladman, DD. “Psoriatic arthritis.” New England Journal of Medicine. March 9, 2017. DOI: 10.1056/NEJMra1505557.
  2. Scher JU, Ogdie A, Merola JF, Ritchlin CT, Preventing psoriatic arthritis: focusing on patients with psoriasis as increased risk of transition. Nature Reviews: Rheumatology. 2019; 15, 153-166. https://www.nature.com/articles/s41584-019-0175-0 Accessed July 22, 2019.
  3. 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.
  4. Ritchlin, CT, Colbert, RA, and Gladman, DD. “Psoriatic arthritis.” New England Journal of Medicine. March 9, 2017. DOI: 10.1056/NEJMra1505557.
  5. Yan D, Issa N, Afifi L, Jeon C, Chang HW, Liao W. The Role of the Skin and Gut Microbiome in Psoriatic Disease. Curr Dermatol Rep. 2017;6(2):94–103. doi:10.1007/s13671-017-0178-5
  6. Scher JU, Ubeda C, Artacho A, et al. Decreased bacterial diversity characterizes the altered gut microbiota in patients with psoriatic arthritis, resembling dysbiosis in inflammatory bowel disease. Arthritis Rheumatol. 2015;67(1):128–139. doi:10.1002/art.38892
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