Psoriatic arthritis

• Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. It can vary in severity from mild stiffening and soreness in the joints to complete joint destruction in arthritis mutilans.
• 10-20% of patients with psoriasis will develop psoriatic arthritis
• The pattern of joint inflammation differs:

  • Asymmetrical oligoarthritis
  • Symmetrical polyarthritis (similar to RA)
• Arthritis mutilans:

  • Most severe form of psoriatic arthritis
  • Affects the phalanges
  • Osteolysis (destruction) of the bones around the joints
  • Progressive shortening of the digits
  • Skin folds as the digit shortens - "telescopic" digit
• Psoriatic arthritis tends to affect the distal interphalangeal (DIP) joints and axial skeleton, whereas rheumatoid arthritis tends not to affect these joints. This can help you distinguish them.
• Signs:

  • Plaques of psoriasis on the skin
  • Nail pitting
  • Onycholysis (separation of the nail from the nail bed)
  • Dactylitis (inflammation of the entire finger)
  • Enthesitis (inflammation of the entheses which are the points of insertion of tendons into bone)
• The NICE guidelines on psoriasis (2017) suggest the Psoriasis Epidemiological Screening Tool (PEST) as a way of screening for psoriatic arthritis in patients with psoriasis. 
• X-ray changes - characteristic "pencil-in-cup" appearance

  • Periostitis (inflammation of the periosteum, causing a thickened and irregular outline of the bone)
  • Ankylosis (fixation or fusion of the bones at the joint)
  • Osteolysis (destruction of bone)
  • Dactylitis (inflammation of the whole digit, seen as soft tissue swelling)
• The classic x-ray finding in the digits is a “pencil-in-cup” appearance. There is erosion of the bones at the joint. There is central erosion on one side of the joint, giving a cup-like appearance. The other bone becomes pointed and looks like a pencil in the cup. This appearance is associated with arthritis mutilans.
• Management depends on severity:

  • NSAIDs
  • Steroids
  • DMARDs
• Psoriatic arthritis is part of the seronegative spondyloarthropathy group of conditions. It may be associated with extra-articular manifestations, particularly uveitis and inflammatory bowel disease.