Psoriatic Arthritis

 

• Pathophysiology and epidemiology

  • A type of peripheral spondyloarthritis. Spondyloarthritis (SpA) is a group of autoimmune conditions involving arthritis (primarily enthesitis, where tendon meets bone) and extra-articular manifestations. SpA can be axial – primarily affecting the spine – or peripheral (psoriatic, reactive, or enteropathic), though both may have features of the other.
  • Affects around 15% of people with psoriasis, and may present before skin signs.

• Presentation

  5 patterns:

  • Asymmetric oligoarthritis: commonest pattern.
  • Symmetrical polyarthritis, similar to RA. Also common.
  • Sacroiliitis, similar to ankylosing spondylitis.
  • DIP joint disease.
  • Arthritis mutilans: joint deformity and destruction.

  Signs:

  • Dactylitis: sausage fingers or toes.
  • Onycholysis: distal nail detachment, preceded by yellow/brown discolouration.
  • Nail pitting. Usually on same finger as DIP swelling; DIP swelling without nail changes is more characteristic of nodal osteoarthritis.

• Risk factors

  • Family history of psoriasis and/or SpA.
  • Association with other autoimmune diseases: psoriasis, IBD, uveitis.

• Investigations

  • X-ray: DIP erosion leading to 'pencil-in-cup' appearance. If X-ray normal, consider US and/or MRI of affected sites.
  • ↑ESR, ↑CRP.
  • HLA-B27 (60-90% sensitive) may help support the diagnosis.

• Management

  • Oligo- or polyarthritis is managed essentially like rheumatoid arthritis (RA): cDMARDs → combination cDMARDs → bDMARDs (anti-TNFα then ustekinumab [anti-IL12 and IL-23]). NSAIDs can be used as an adjunct.
  • Monoarthritis can initially be treated with local steroid injections.