Psoriatic Arthritis



Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. This can vary in severity. Patients may have a mild stiffening and soreness in the joint or the joint can be completely destroyed in a condition called arthritis mutilans.

It occurs in 10-20% of patients with psoriasis and usually occurs within 10 years of developing the skin changes. It typically affects people in middle age but can occur at any age.

It is part of the “seronegative spondyloarthropathy” group of conditions.

 

Patterns

The condition does not have a single pattern of affected joints in the same way as osteoarthritis or rheumatoid. There are several recognised patterns:

Symmetrical polyarthritis presents similarly to rheumatoid arthritis and is more common in women. The hands, wrists, ankles and DIP joints are affected. The MCP joints are less commonly affected (unlike rheumatoid).

Asymmetrical pauciarthritis affecting mainly the digits (fingers and toes) and feet. Pauciarthritis describes when the arthritis only affects a few joints.

Spondylitic pattern is more common in men. It presents with:

  • Back stiffness
  • Sacroiliitis
  • Atlanto-axial joint involvement

Other areas can be affected:

  • Spine
  • Achilles tendon
  • Plantar fascia

 

Signs

  • Plaques of psoriasis on the skin
  • Pitting of the nails
  • Onycholysis (separation of the nail from the nail bed)
  • Dactylitis (inflammation of the full finger)
  • Enthesitis (inflammation of the entheses, which are the points of insertion of tendons into bone)

 

Other Associations

  • Eye disease (conjunctivitis and anterior uveitis)
  • Aortitis (inflammation of the aorta)
  • Amyloidosis

 

Psoriasis Epidemiological Screening Tool (PEST)

NICE recommend patients with psoriasis complete the PEST tool to screen for psoriatic arthritis. This involves several questions asking about joint pain, swelling, a history of arthritis and nail pitting. A high score triggers a referral to a rheumatologist.

 

Xray Changes

  • Periostitis is inflammation of the periosteum causing a thickened and irregular outline of the bone
  • Ankylosis is where bones joining together causing joint stiffening
  • Osteolysis is destruction of bone
  • Dactylitis is inflammation of the whole digit and appears on the xray as soft tissue swelling
  • Pencil-in-cup appearance

The classic xray change to the digits is the “pencil-in-cup appearance”. This is where there are central erosions of the bone beside the joints and this causes the appearance of one bone in the joint being hollow and looking like a cup whilst the other is narrow and sits in the cup.

 

Arthritis Mutilans

This is the most severe form of psoriatic arthritis. This occurs in the phalanxes. There is osteolysis (destruction) of the bones around the joints in the digits. This leads to progressive shortening of the digit. The skin then folds as the digit shortens giving an appearance that is often called a “telescopic finger”.

 

Management

Management is similar to rheumatoid arthritis. There is a crossover between the systemic treatments of psoriasis and treatment of psoriatic arthritis. Treatment is often coordinated between dermatologists and rheumatologists.

Depending on the severity the patient might require:

  • NSAIDs for pain
  • DMARDS (methotrexate, leflunomide or sulfasalazine)
  • Anti-TNF medications (etanercept, infliximab or adalimumab)
  • Ustekinumab is last line (after anti-TNF medications) and is a monoclonal antibody that targets interleukin 12 and 23

 

Last updated April 2019
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