Psoriatic Arthritis — Basic Facts

Epidemiology of psoriatic arthritis

Estimates vary on how many people with psoriasis develop psoriatic arthritis (PsA), in part because the disease presents with a wide variety of symptoms among patients and diagnosis may be missed or delayed.1,2 A recent epidemiological survey found that 11% of patients with psoriasis had PsA; however, this survey only counted patients as having PsA if they had received an official diagnosis.1 Other reports of the incidence of psoriatic arthritis vary between 6% and 42%, noting that the lower estimates may reflect a missed diagnosis or misdiagnosis (receiving the wrong diagnosis, such as rheumatoid arthritis).2,3

In one study that assessed the prevalence of PsA in 1,511 patients with psoriasis, 21% had existing PsA and 85% of those cases had been diagnosed for the first time during the course of the study.4 Psoriasis patients who were routinely treated at a dermatology clinic were evaluated by a rheumatologist in another study where 30% were diagnosed with PsA and 41% of those cases had not been aware of the diagnosis previously.2

Psoriatic arthritis is thought to occur in up to 1% of the general population, with survey results indicating that approximately 1 million adults in the U.S. have PsA. 3,5 While the distribution of the disease across ethnicities has not been studied, whites are known to be more commonly affected than are persons of other racial groups. Men and women are equally affected. PsA generally develops in people aged 35-55 years, but it can occur at any age. In the juvenile form of the disease, PsA develops at 9-11 years of age.5

Statistics on symptoms of psoriatic arthritis

  • Nail lesions occur in about 87% of people diagnosed with psoriatic arthritis. 3
  • Inflammation causing a sausage-shape to the fingers or toes (dactylitis) occurs in up to 50% of patients with PsA and is a marker for disease progression. 2
  • Inflammation at attachment sites for tendons, ligaments, or joint fiber capsules (enthesitis) occurs in up to 50% of people living with PsA. 6
  • PsA affecting the neck and back (cervical spondylitis) occurs in 35%-75% of people with the disease. 7
  • Spinal involvement, including inflammation between the vertebrae in the spine (spondylitis) and/or between the spine and the pelvis (sacroiliitis), occurs in up to 40% of people with PsA.10

Statistics on the progression of psoriatic arthritis

  • PsA is a progressive disease, and 55% of those living with the disease will develop five or more deformed joints in 10 years or more.3
  • Skin psoriasis precedes the onset of psoriatic arthritis (PsA) in 84% of patients with psoriasis.8
  • In about 10-15% of cases, PsA will develop before psoriasis.2
  • It has been reported that there is a subset of patients with PsA who may achieve remission for at least 12 months. These cases tend to be men with a lower number of actively inflamed joints at diagnosis. However, after an average of 2.6 years, 52% of these patients had flares, and only 6% sustained a complete, prolonged remission without medications.3
  • PsA is severe in at least 20% of people living with the disease. Cases with severe disease are defined by the number of joints affected, usually four or more.3,9
Written by: Emily Downward | Last reviewed: October 2016.
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