Definition
Inflammatory arthritis associated with psoriasis and one of the Spondyloarthropathies, involving peripheral joints, entheses and the axial skeleton.
Aetiology
- HLA-B27 linked to axial disease
- IL-23 and IL-17 pathway drives inflammation
- Trauma may trigger joint flares, the deep Koebner phenomenon
Epidemiology
- Up to 30% of people with psoriasis
- Skin disease precedes arthritis in most cases
- Men and women affected equally
Classification
- Moll and Wright asymmetric oligoarthritis
- Moll and Wright symmetric polyarthritis resembling rheumatoid arthritis
- Moll and Wright DIP joint predominant disease
- Moll and Wright spondylitis and sacroiliitis
- Moll and Wright arthritis mutilans
- CASPAR needs inflammatory articular disease and 3 or more points
- CASPAR current psoriasis scores 2, or a personal or family history scores 1
- CASPAR nail dystrophy, dactylitis and negative rheumatoid factor score 1 each
- CASPAR juxta-articular new bone formation on radiographs scores 1
- CASPAR specificity 98.7% and sensitivity 91.4%
Clinical Features
- Dactylitis, the sausage digit
- Enthesitis, often at the Achilles and plantar fascia
- Nail pitting and onycholysis
- Uveitis
Investigations
- Rheumatoid factor and anti-CCP negative in most
- CRP raised in active disease
- Radiographs show pencil in cup deformity, periostitis and asymmetric sacroiliitis
Differential Diagnosis
- Rheumatoid arthritis
- Ankylosing spondylitis
- Reactive arthritis
- Gout
- Erosive osteoarthritis of the DIP joints
Management
- NSAIDs. Mild peripheral and axial symptoms
- Conventional DMARDs. Methotrexate for peripheral arthritis
- Biologics. TNF, IL-17 or IL-23 inhibitors for refractory or axial disease
- Arthroplasty or fusion. Destroyed joints, avoiding incisions through active plaques
- Perioperative drugs. Biologic timing around surgery, see Perioperative Rheumatological Medications
References
- Taylor W, Gladman D, Helliwell P, Marchesoni A, Mease P, Mielants H, CASPAR Study Group. Classification criteria for psoriatic arthritis. Development of new criteria from a large international study. Arthritis Rheum. 2006, 54(8), 2665-73. PubMed
- Ritchlin CT, Colbert RA, Gladman DD. Psoriatic arthritis. N Engl J Med. 2017, 376(10), 957-70. PubMed
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 19 October 2026.