Introduction

Psoriasis is an autoimmune condition which affects the skin and joints. It is sometimes referred to as one of the spondyloarthritides (inflammatory arthritis that is seronegative for rheumatoid factor (and/or does not fit the criteria for diagnosis as RA)).

Definitions

  • Psoriasis – umbrella term for the condition, but often used to describe the disease when only skin lesions are present. Affects 1-3% of the population
  • Psoriatic arthritis – describes the joint involvement of the condition

Skin changes

  • Inflammation and production of excess skin, causes characteristic erythematous lesions, with silvery ‘plaques’.
  • Plaques are common at the knees and elbows, but can occur anywhere
    • Unlike eczema, they tend to occur on extensor surfaces, and around pressure points.

Nail changes

  • Psoriatic nail dystrophy – particularly associated with psoriatic arthritis, and rarer in patients who suffer only skin changes.
  • The nails will often be discoloured (a yellow/brown patchy colour)
  • May also be onycholysis
  • May be ‘pitting’ – small (needle sixed) little pits in the nail surface
  • Subungal hyperkeratosis – where there is proliferation of the deeper keratine layers of the nail – causing the smooth nail surface to be raised, whilst a mesh of keratin grows underneath.
  • ridging

Psoriatic Arthritis

Epidemiology and Aetiology

  • Genetic component
    • Often a family history – which can aid the diagnosis
    • HLA-B27 – present in 50% of those with spinal signs
  • Cause basically unknown
  • Smoking and excessive alcohol intake may increase the risk of getting the condition
  • Often associated with:

Clinical features

  • Can essentially present with any variation of arthritic symptoms!
    • Often indistinguishable from RA, but is seronegative, and in association with skin signs, should be considered a separate condition.
    • Usually an oligoarthritis (2-5 joints, usually asyymetrical), usually weight bearing joints.
  • Check for psoriatic skin lesions, may not be obvious, and patients themselves may not even know they have them. Check specifically the
    • Natal Clef
    • Scalp
    • Umbilicus
  • Check for nail changes
  • In a minority of cases, the arthritis presents before skin and nail changes. In which case, you may be able to identify typical features of spondyloarthritides:
    • Dactylitis – literally – sausage shaped digit – results from inflammation of the whole finger
    • Enthesopathy – involvement of the enthesis. Can include enthesitis.
  • Osteolysis – perhaps the most characteristic sign. As the bone in the fingers is lost, there may be telescoping of the fingers
  • Spinal involvement – typically at the sacrum

Investigations

  • Synovial biopsy – not routinely performed, but will show pathological differences from rheumatic conditions, even when the disease closely resembles RA.
  • Radiographs – may show osteolysis, which appears as a ‘pencil-in-cup’

Treatment

  • Essentially follows that of the condition of which features are most prominent…
  • Treat as if RA – if RA signs are prominent
    • Methotrexate and leflunomide are the DMARD’s of choice. Hydrochlorequine is avoided as it exacerbates skin disease
    • Evidence for the efficacy of DMARD’s in PsA is not very conclusive
    • Anti-TNF-α treatments have not been used for very long, but look very promising!
  • o   Treat as if AS – if AS signs are prominent

Prognosis

  • PsA patients score slightly worse on QOL scores than the general population:
    • 1.0 is average value for general population
    • 0.9 is Psa
    • 0.8 in RA
  • Slight increased mortality (1.6x normal risk)
    • Mainly due to increased risk of cardiovascular disease

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