Psoriatic arthritis (PsA) is a chronic, inflammatory condition associated with psoriasis, an inflammatory skin disorder characterized by a red, scaly rash most often occurring on the extensor surfaces of the skin and scalp. Up to 6-48% of patients with psoriasis may develop PsA, presenting with pain and stiffness of the affected joints.4 Sometimes patients develop arthritis before the psoriatic skin changes. PsA was distinguished from rheumatoid arthritis (RA) with the discovery of rheumatoid factor (RF). Eighty-five percent of RA patients are RF-positive; PsA patients are usually seronegative for RF. PsA affects primarily fingers and toes, occasionally sacroiliac joints, and may progress to spondylitis. Other clinical signs of psoriatic arthritis include fingernail deformities, fusiform, digital swelling (psoriatic dactylitis), autofusion of finger joints or wrist joints, MP joint hyperextension and digital shortening (opera glass hand deformity).
Pathophysiology
Structural changes observed with PsA include a pattern of increased vascularity of the synovial membrane distinguishable from that observed with RA, infiltration by a variety of leukocytes, and development of destructive pannus. Early inflammatory processes may be a result of the innate immune response, involving several cytokines including tumor necrosis factor alpha (TNF-a) and interleukins IL-1, IL-8, and IL-15. The acquired immune response may also play a role, with CD8+ T lymphocytes implicated.
Related Anatomy
- Nalebuff described three types of psoriatic arthritis in the Hand:
- Ankylosing
- Osteolytic
- Rheumatoid arthritis-like deformities with stiffness
Related X-ray Changes
- Soft tissue swelling and osteoporosis
- Joint narrowing and marginal erosions which later widen and produce pencil-in cup joint deformities
Incidence and Related Conditions
- Prevalent in 1−2% of population (up to 40% of people diagnosed with psoriasis)
- PsA affects young adults of either gender
- Higher risk of gout as co-morbidity
- Called psoriatic juvenile idiopathic arthritis (JIA) when presenting with psoriasis in children
Differential Diagnosis
- Rheumatoid arthritis
- Osteoarthritis
- Fibromyalgia
- Gout
- Arthritis mutilans