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)).
- 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
- 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.
- 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.
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:
- 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
- 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
- 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’
- 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