Characteristics

• Affects 5%–10% patients with psoriasis.

• This is a proliferative synovitis.

• Early fibrosis is common.

• Classified as a seronegative spondyloarthropathy.

• HLA B27 is positive in the majority of patients.

• May mimic rheumatoid arthritis.

Clinical features

• Skin rash commonly precedes arthritis.

• Nail changes include pitting, hyperkeratosis, ridging and subungal separation.

• Joint changes are similar to rheumatoid arthritis although rheumatoid nodules are absent.

• Characteristically a mild asymmetrical polyarthritis typically affecting the distal interphalageal joints of the hands and feet.

• Bone destruction may be severe (arthritis mutilans).

• Sacroiliitis may mimic ankylosing spondylitis.

Radiological features

• Within the large joints, changes are similar to rheumatoid arthritis.

• Bone density tends to be preserved.

• Psoriatic dactylitis = soft-tissue swelling of entire digit – ‘sausage digit’.

• Interphalangeal joint destruction secondary to erosions and periosteal new bone formation results in ‘pencil in cup’ deformity.

• Sacroiliac erosions are common.

Management

• Specialised care under the guidance of a rheumatologist.

• Treatment aimed at symptom control. NSAIDS are the mainstay of treatment.

• Immunosuppressant drugs (e.g. methotrexate) for resistant disease – current research therapies include anti-tumour necrosis factor.

• Physiotherapy and the use of splintage can help prevent deformity and functional loss.

• Most psoriatic arthropathy is burnt out in 10 years.

• Surgery for pain, instability and to improve function (arthrodesis/arthroplasty).