Psoriatic skin disease is a relatively common condition for which the treatments are somewhat unpleasant and not entirely effective. It is known that an arthritic syndrome is associated with this skin disorder but even then the diagnosis may be missed when patients with psoriasis present with joint signs. There are many effects from psoriatic arthritis on the joints and the arthritic damage can lead to disability and compromised quality of life. In the United Kingdom the prevalence of psoriasis itself is around 2%, with 14% of this number exhibiting some signs of involvement in their joints.
Even before the skin condition becomes obvious there can be signs of joint involvement in around fifteen percent of sufferers and even without joint involvement soft tissues can show changes which are typical in the arthritis. Rheumatoid arthritis sufferers typically have a greater number of joints affected than in psoriatic arthritis, with perhaps a similar pattern presentation and in some examples only one or two joints are involved. The most involved anatomical areas are the entheses, which are the connections between the bones and the ligaments and tendons. The Achilles tendon is the largest enthesis in the body and commonly affected by inflammatory changes and pain.
There are a large number of entheses in the body and these may be responsible for the more widely spread symptoms which can occur without joints being involved. There can be individual finger swelling with or without changes in other joints and this is a negative indication for disease progression. Back pain or inflammatory spondylitis can be similar to that of ankylosing spondylitis and the symptoms are worse with resting and better with exercising, significant stiffness in the early mornings, a slow and gradual onset and pain worse at night. About 30% of patients can have anatomical back changes without pain or problems and involvement of the nails and distal finger joints in the disease occurs also.
As people get older they increasingly complain of joint problems so it is easy to miss the signs in a person with psoriasis. A clinician should always be suspicious of the possibility of psoriatic arthritis in any patient with psoriasis who presents with a musculoskeletal complain, particularly if it involves the end finger joints or they have back pain which appears inflammatory. The ESR (erythrocyte sedimentation rate) and the CRP (C-reactive protein) blood tests are routine investigations and both can be elevated in inflammatory conditions. If a joint condition is suspected and there are no signs of psoriasis it is wise to carefully check the person’s body for hidden signs of psoriatic skin lesions to exclude this highly genetic condition.
Typically 30% of people diagnosed with this condition will suffer with non-progressive disease in a few affected joints. This presentation is usually effectively treated with steroid injections into the joints as required and by symptomatic management. Identifying this group initially is important to exclude those with worse disease who are likely to show increased inflammatory blood markers, to be male, to have a larger number of affected joints and to have used steroids previously. If showing these negative factors they are more likely to develop damaging disease to the joints with increased disability and a reduction in their quality of life.
Psoriatic arthritis sufferers have benefited less from research and development that those who have other major arthritic conditions but over the last ten years there has been a large increase in investigations concerning this disease. Development of the recent biological treatment agents has stimulated new treatment methods. Despite this there is still a lack of evidence for treatments and when to apply them.
Research and development in rheumatoid arthritis has historically been well ahead of that for psoriatic arthritis but this picture is changing quickly with large numbers of published papers over the last ten years. The instigation of the biological treatment drugs has also encouraged new diagnostic and treatment options. We have however not achieved clear treatment protocols or good evidence for some treatments.