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.
Psoriatic arthritis occurs in 10-20% of patients with psoriasis, usually within 10 years of developing the skin condition. Arthritis can occur before the skin changes. It is most common in middle age but can occur at any age.
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.
Patterns
There are 5 recognised patterns. Asymmetrical oligoarthritis and symmetrical polyarthritis are the most common.
Asymmetrical oligoarthritis affects 1-4 joints at any given time, often on only one side of the body.
Symmetrical polyarthritis presents similarly to rheumatoid arthritis. More than four joints are affected, such as the hands, wrists and ankles.
Distal interphalangeal predominant pattern primarily affects the DIP joints. However, the DIP joints can be affected across all types of psoriatic arthritis.
Spondylitis presents with back stiffness and pain. It involves the axial skeleton (spine and sacroiliac joints).
Arthritis mutilans is the most severe form of psoriatic arthritis. It affects the phalanges (the bones of the fingers and toes). There is osteolysis (destruction) of the bones around the joints, leading to progressive shortening of the digits. The skin folds as the digit shortens, giving an appearance described as a telescoping digit.
TOM TIP: 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 (tiny indents in the fingernails and toenails)
- 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)
Psoriasis Epidemiological Screening Tool
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. It involves questions about joint pain, swelling, a history of arthritis and nail pitting. A high score triggers a referral to a rheumatologist.
X-ray Changes
Characteristic x-ray changes in psoriatic arthritis include:
- 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
There is a crossover between the systemic treatments used to treat the skin condition and psoriatic arthritis. Treatment is coordinated between dermatologists, rheumatologists and other multidisciplinary team members.
Depending on the severity, treatment may involve:
- Non-steroidal anti-inflammatory drugs (NSAIDs)
- Steroids
- DMARDs (e.g., methotrexate, leflunomide or sulfasalazine)
- Anti-TNF medications (etanercept, infliximab or adalimumab)
- Ustekinumab is a monoclonal antibody that targets interleukin 12 and 23
Last updated August 2023