Psoriatic Arthritis

An inflammatory arthritis associated with psoriasis, usually seronegative for rheumatoid factor, sharing many clinical aspects with the other seronegative arthropathies.

Although generally not thought to be as severe as rheumatoid arthritis, patients with PsA are at risk of deformity and significant loss of function.

Epidemiology

  • Prevalence of psoriasis in the general population is around 2-3%
    • Prevalence amongst those with arthritis is around 7%
    • Prevalence or arthritis amongst those with psoriasis is reported between 6-42% (wide due to lack of definition); 30% is the estimated value
  • The exact prevalence of psoriatic arthritis is not known but reports vary from 0.04%-0.1%. (incidence around 3.4-8 per 100,000)
  • Age of onset is between 30-55 years; equal sex distribution
  • Majority (70%) of patients will present with psoriasis before arthritis; Around 15% will present with arthritis before psoriasis and 15% will develop the conditions together.

Pathophysiology/Aetiology

  • Genetic factors
    • Strong hereditary component
    • Linked the HLA-B38/B39 (peripheral PsA) and HLA-B27 (spondylitis PsA)
  • Viral/infective role is possible but no specific viruses have been identified
  • Immune factors
    • PsA is associated with lymphocytic infiltration of the skin, joints and entheses.  This is mainly involves T-cells (CD4+ T cells) and their inflammatory cytokines e.g. TNF, IL-1, IL-6, IL-1B, IL-10 etc).

Presentation

Musculoskeletal

  • Inflammatory arthritis- i.e. painful, hot, swollen, erythematous joints
    • NB joints are usually less painful/tender than in rheumatoid
    • Joints are also more likely to present in a ‘ray’ distribution i.e. all the joints of one digits affected rather than the same joints of both hands (more typical of RA)
    • However, like RA, symptoms do worsen at rest/night and improve with movement
  • Can be classified as
    • Asymmetrical oligoarticular arthritis
      • Most common presentation, affecting the hands and feet first
        • Asymmetrical knee involvement is also seen
      • Inflammation may involve the tendons, tendon sheaths and entheses, causing a dactylitis appearance (sausage-fingers)
    • Symmetrical Polyarthritis
      • Rheumatoid like in presentation but
        • more commonly DIP>PIP joint involvement; relatively asymmetrical; no nodules
    • DIP arthritis
      • Isolated DIP involvement is less common but can occur
      • Often associated with dactylitis and nail dystrophy (paronychia)
    • Spondylitis +/- sacroiliitis (+/- peripheral arthritis)
      • Occurs in 5-36% of patients with PsA
      • Unlike ankylosing spondylitis, spinal involvement can be asymmetrical and features of sacroiliitis may be minimal or absent
      • Radiological features, too, are less obvious in PsA and are more likely to show discrete foci of affected spine rather than the caudo-cranial progression seen in Ank Spon
    • Arthritis mutilans
      • Rare, rapidly deforming form of arthritis (1-5% of patients)
      • Caused by resorption of the bone- giving a ‘pencil in cup’ appearance on x-ray and a telescopic movement of the digit
  • Enthesitis is a major feature of PsA
    • Achilles tendonitis and plantar fasciitis are common manifestations

Extra-articular features

  • By definition- PsA should be associated with psoriasis (a diagnosis, however, can still be made based on family history and presentation of symptoms)
  • Anterior uveitis
  • SAPHO syndrome
    • synovitis
    • acne
    • pustulosis
    • hyperostosis
    • osteitis

Investigations

  • There are no specific investigations for PsA- diagnosis is primarily clinical
  • Inflammatory markers can be elevated
  • X-ray changes
    • bony erosions at the edge of cartilage, often asymmetrical
    • bony ankylosis/joint subluxation may also be seen
  • MRI may be useful in evaluating the soft tissue changes

Management

  • NSAIDs are recommended for symptomatic treatment
  • Intra-articular steroids may be used second line.  NB Oral corticosteroids should be avoided as psoriasis rash may rebound upon treatment withdrawal.
  • DMARDS
    • Early treatment with DMARDS should be considered for peripheral arthritis and enthesitis, +/- skin/nail disease.
    • Ideally treat both the skin and musculoskeletal symptoms (if both are present)
      • Methotrexate is often the best treatment for this reason
    • Antimalarial DMARDs e.g. hydrochloroquine should be avoided as these can cause skin reactions (exfoliative dermatitis) that may worsen psoriasis
    • If just arthritis symptoms are present- leflunomide may be a better option for active peripheral arthritis
  • Physiotherapy plays a role in axial disease
  • Biologic agents (only anti-TNF agents for psoriatic arthritis) may be offered to patients
    • with active arthritis (>=3 tender/swollen joints) which has not responded to at least 2 DMARDs (alone or in combination), one usually being methotrexate
      • OR after 1 DMARD if there is one of:
        • >=5 joints; elevated CRP >3 months; or structural bone damage due to disease
    • with active enthesitis and/or dactylitis which has not responded to NSAIDs or local steroid injection
    • with predominantly axial disease that is active and has not responded to NSAIDs
      • NB treatment should be stopped if there is an inadequate response
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s