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Psoriatic Arthritis

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Overview

Psoriatic arthritis (PsA) is a seronegative inflammatory arthritis affecting joints and connective tissue and is associated with psoriasis of the skin or nails. PsA can occur without the presence of skin disease, or the rash may be difficult to notice.

PsA may affect the tendons surrounding the joints as well as the joints themselves. This can lead to swelling of the whole digit (dactylitis) or enthesitis (inflammation of the entheses, the sites where tendons or ligaments insert into the bone).

It is a progressive disorder ranging from mild synovitis to severe progressive arthropathy. Around 40-60% of patients with psoriatic arthritis develop erosive and deforming joint complications.

Epidemiology

  • Affects 20-30% of people with psoriasis
  • There isn’t a strong correlation between the severity of psoriasis and the development of arthritis
  • More common in 35-55 years of age, but can happen to anyone of any age

Risk Factors & Associations

  • Psoriasis
  • Family history of psoriatic arthritis
  • HLA-B27
  • Obesity
  • Smoking

Presentation

Suspect PsA in a patient with inflammatory-type joint pain with dactylitis. Other features include:

  • Psoriatic nail disease:
    • Pitting of nails
    • Onycholysis
  • Dactylitis – swelling of a digit (sausage-like swelling)
  • Inflammatory joint pain:
    • Prolonged morning stiffness >30 minutes
    • Improvement with use
    • Recurrence with prolonged rest
  • Monoarticular or oligoarticular joint involvement
  • Spinal stiffness and sacroiliitis

Signs on examination

  • Swelling and tenderness (synovitis) of joints
  • No rheumatoid nodules present
  • Psoriatic skin lesions present
  • Nail changes such as pitting and onycholysis present
  • Enthesitis may be seen
  • Spinal stiffness may be seen

Patterns of presentation

Psoriatic arthritis can be difficult to diagnose, as it has multiple disease patterns. 

  • Symmetrical polyarthritis – similar to rheumatoid arthritis
    • More common in women
    • Distal interphalangeal joints (DIPs) are more involved than metacarpophalangeal joints (MCP)
    • Absence of skin nodules and negative serology (no rheumatoid factor/anti-CCP)
  • Asymmetric oligoarticular arthritis
    • Usually, the hands and feet are affected initially
    • This affects up to 5 joints
  • Lone DIP disease
    • The nail and surrounding skin can be involved
  • Arthritis mutilans
    • This is relatively rare
    • Radiology shows a “pencil-in-cup” appearance
  • Spondylitis pattern with or without sacroiliitis
  • Juvenile onset
    • Usually starts as a monoarthritis, but a DIP pattern can be seen
    • Tenosynovitis and nail changes can be present
    • If the epiphyses are involved, it can affect growth

Differential Diagnoses

Rheumatoid arthritis (RA)

  • RA generally presents with a symmetrical polyarthritis affecting small joints of the hands and feet
  • RA does not have dactylitis, skin, or nail changes
  • RA does not affect the lumbar spine or sacroiliac joints

Osteoarthritis (OA)

  • The joint pain in osteoarthritis is non-inflammatory (worsens with exertion and improves with rest)
  • OA tends to present in older patients
  • OA does not have dactylitis, skin, or nail changes 

Reactive arthritis

  • There is usually a history of a recent sexually-transmitted infection or gastroenteritis
  • Reactive arthritis is generally an oligoarthritis affecting weight-bearing joints
  • Extra-articular features such as conjunctivitis and urethritis are present 

Gout

  • In gout, there may be a history of an acute and relapsing course of synovitis
  • In gout, the onset is much more acute
  • In gout, gouty tophi may be present
  • In gout, the pattern is usually monoarticular or oligoarticular

Investigations

  • X-ray of hands and feet:
    • Shows erosions in DIP and periarticular new bone formation
    • In advanced disease – “pencil in cup” deformity seen
  • Rheumatoid factor and anti-CCP:
    • Rheumatoid factor may be positive or negative
    • Anti-CCP is negative
  • If monoarthritis, synovial fluid aspiration and analysis:
  • ESR/CRP:
    • May be normal or elevated
  • Tests for metabolic syndrome:
    • Patients with psoriatic arthritis have a higher risk of metabolic syndrome

Management

Overview

Treatment is initiated by a rheumatology specialist. The management of PsA is similar to rheumatoid arthritis except for the following difference:

  • Limited peripheral joint disease: NSAID only, instead of offering all patients a disease-modifying antirheumatic drug (DMARD) as with rheumatoid arthritis
  • As well as the DMARDs available for rheumatoid arthritis, monoclonal antibodies including ustekinumab and secukinumab are possible treatment options

Patient Advice

  • Patients should be educated about the risks and reduction of metabolic syndrome and its associated cardiovascular risk
  • Patients should be educated about the risks of NSAID use and GIT bleeding
  • Patients should be educated about recognising signs of infection and seeking immediate help when using immunosuppressive therapy

Complications

  • Cardiovascular disease
  • Joint destruction and disability
  • Atlantoaxial subluxation and neurological sequelae

Prognosis

  • Aggressive treatment of early-stage progressive psoriatic arthritis can help to improve the prognosis

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