Psoriatic arthritis

It is thought that between 6% and 10% of those with psoriasis suffer from inflammatory arthritis known as PSA or psoriatic arthropathy (Figure 8.8). However, it is also thought that the number who suffer from general joint stiffness is more like 33% (Osborn and Wilke, 2004). The pathogenic mechanisms which cause PSA include, like those in the skin, chemical mediators for inflammation and the interaction of T-cells and macrophages. Clinically it may appear as rheumatoid arthritis, although crucially the patient remains seronegative. Those people who have PSA are also very likely to have nail involvement (80%) and that nail involvement is often very destructive. The majority (66%) find that the joint involvement occurs after the lesions appear on the skin; however, for 15% it is around the same time as the cutaneous signs appear and for 15% it is before there are any cutaneous lesions. The different clinical presentations of PSA are outlined in Box 8.1.

Box 8.1 Clinical presentations of PSA Symmetric polyarthritis Looks and behaves almost exactly like rheumatoid arthritis; Generally affects the proximal joints of the fingers, but can affect any joint; Is the most common form of PSA. Asymmetric oligoarticular arthritis Oligo means few, thus this type of arthritis by definition must affect five or fewer joints; Dactylis may be seen, this describes the ‘sausage’ shape of fingers or toes when the distal interphalangeal joint is affected; Later onset of oligoarticular arthritis in large joints has the best prognosis. Distal interphalangeal joint arthritis This could be described as the ‘classic’ appearance of PSA, where only the distal interphalangeal joints are affected. It affects around 5% of those with PSA. Arthritis mutilans A highly destructive form of PSA, there is osteolysis (dissolution of the bone) in the small joints of the hands; Occurs in 1–2% of those with PSA; Seems to be linked to early onset disease and has a poor prognosis. Spondylitis and sacroiliitis On X-ray, changes seem to be consistent with ankylosing spondylitis and sacroiliitis; however symptoms may be absent.

Mild to moderate arthritis may be successfully managed using non-steroidal anti-inflammatory drugs. More severe disease is likely to need to be managed by a rheumatologist and will involve systemic treatments similar to those used to treat cutaneous disease.