Psoriatic arthropathy is a chronic inflammatory, seronegative spondyloarthopathy associated with psoriasis. It occurs in 10-40% of patients with psoriasis and can present without skin changes.
Classification of Psoriatic Arthropathy
| Classification | Description |
|---|---|
| Oligoarthritis | Affects less than 5 joints and tends to be asymmetrical. This is the most common pattern. |
| Symmetrical polyarthritis (’Rheumatoid pattern’) | Affects distal interphalangeal joints (DIPs) more than metacarpophalangeal joints (MCPs) as in Rheumatoid arthritis. |
| DIP predominant | Mostly affects the DIP joints. More often in men |
| Spondyloarthritis | Back pain due to inflammation fo the vertebrae (spondylitis) +/- inflammation of the sacroiliac joint (sacroiliitis) |
| Arthritis mutilans | A rare form causing severe deformity of the hands. Fingers appear ‘telescopic’ since the terminal phalanges are destroyed. |
Classification Criteria for Psoriatic Arthritis (CASPAR): ≥ 3 points are needed to classify the patient as having psoriatic arthritis. This criterion has a sensitivity of ~ 91% and specificity of ~ 98%
- Evidence of psoriasis
- Psoriatic nail changes – 1 point
- Negative rheumatoid factor – 1 point
- Dactylitis – 1 point
- Plain radiograph showing juxta-articular new bone formation (excluding osteophytes) – 1 point
- Risk factors
- Family history of psoriatic arthritis
- HLA-B27 and HLA-B39 alleles
- Trauma to joints or tendons
- Infection e.g. HIV
- Pathophysiology
- Inflammation → hypervascularization of the synovium
- Signs and symptoms
- Psoriatic rash or nail changes
- Acneiform rashes and palmo-plantar pustulosis
- Joint pain
- Worse after long periods of rest
- Morning stiffness > 30 minutes
- Improves with activity
- Tenderness and swelling of joints
- Dacylitis
- Enthesitis (elbow, heel, or lateral hip pain)
- Differentials
- Rheumatoid arthritis
- Reactive arthritis
- Gout
- Investigations
- ESR/CRP
- Raised in active disease
- Normal ESR/CRP does not exclude psoriatic arthritis
- Rheumatoid factor: non-specific for rheumatoid arthritis
- Negative
- Positive in 10% of patients
- Anti-CCP: more specific for rheumatoid arthritis
- Negative
- Positive in 8 – 16% of patients
- HLA-B27
- Positive
- A negative test does not exclude psoriatic arthritis
- X-ray of the hands, feet +/- sacroiliac joint
- DIP joint erosion with ‘pencil-in-cup’ deformity in advanced disease/arthritis mutilans
- Periarticular new-bone formation
- Ultrasound
- Tendon swelling
- Increased blood flow and erosions
- MRI
- ESR/CRP
- Treatment
- NSAIDs may be used alone
- DMARDs can be combined if necessary (first line)
- Methotrexate, leflunomide, or sulfasalazine (first line)
- Biological agents (etanercept, infliximab, apremilast) are second-line
- Short course of oral corticosteroids to bridge DMARD therapy
- Physiotherapy and occupational therapy
- Complications
- Joint deformity
- Functional limitation
- Cardiovascular complications
- Hypertension and ischaemic heart disease
- Diabetes
- Obesity
- Increased risk of skin cancer due to treatment with DMARDs
