Psoriasic arthritis

Psoriasis is a common skin disease in which scaly patches of erythema form. The areas where they most frequently appear are the scalp, elbows, knees and lower back. Some cases are so mild that they can go unnoticed. In other cases, psoriasis can be very extensive, affecting large areas of the skin.

Despite the fact that psoriasis is basically a skin disease, up to a third of patients who are affected by this disease can suffer from involvement of various joints. When this happens the patient is said to have psoriatic arthritis.

How is it produced?

While patients with psoriasis generally present skin manifestations already during childhood or adolescence, the joint involvement associated with this disease does not usually appear until later, between the ages of 20 and 40. Joint involvement probably has an immunological origin.

It appears that there is a family genetic predisposition to psoriatic arthritis. It has been seen that there is an association with a marker, HLA B27, in patients with psoriatic arthritis with sacroiliitis, be it unilateral or bilateral.

Symptoms

Psoriatic arthritis has several forms of manifesting itself. In all cases, skin involvement precedes arthritis in time. The forms of presentation are:

• Asymmetric oligoarthritis: it is the most frequent form (50%) and affects men and women in equal proportions. Both the upper and lower extremities can be affected in this way. Unlike rheumatoid arthritis, the distal interphalangeal joints are affected as well as the proximal ones. If both joints have arthritis, dactylitis occurs, commonly known as sausage finger. In general there is usually an associated onychopathy, also unlike rheumatoid arthritis.
• Symmetric polyarthritis: affects 25% of patients, predominantly among women. There is a symmetrical involvement in several joints of the upper and lower extremities. Similar in its presentation to rheumatoid arthritis, it differs from it by the existence of onychopathy, the involvement of the distal interphalangeal joints and the absence of subcutaneous nodules.
• Spondylitis: occurs in 25% of patients, mainly in men. It is characterized by involvement of the spine, especially at the lumbar and sacroileal level, associated or not with alterations in peripheral joints. Achilles tendonitis can occur, as in ankylopoietic spondylitis, and there is onychopathy. One third of patients with this form of psoriatic arthritis have intestinal disorders.
• Isolated involvement of the distal interphalangeal: represents 5% of the forms of psoriatic arthritis and in general it tends to evolve into other forms with involvement of more joints.
• Mutilating: 5% of patients present this aggressive form in which destructive arthritis occurs with resorption of the interphalangeal, metacarpal and metatarsal joints. It can appear isolated or associated with other joint alterations.

Diagnosis

The diagnosis should be suspected in all patients with psoriasis who also present alterations of arthritic characteristics in the different forms discussed above.

In the blood analysis, no significant change will be appreciated except the elevation of the acute phase reactants, such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Rheumatoid factor is found in the blood in a quarter of patients with psoriatic arthritis in its symmetric polyarthritis form.

Erosions and decreased joint space will be seen on radiographs of affected joints. Unlike rheumatoid arthritis, there will be no osteoporosis. When there is a resorption of the distal or proximal interphalangeal joints, a characteristic radiological image is created that is called a “pencil-cup”.

Treatment

The treatment of psoriatic arthritis will initially be based on pain control, through the use of non-steroidal anti-inflammatory drugs (NSAIDs) or low-dose corticosteroids.

In cases of severe joint involvement, disease modulating drugs will be used, especially methotrexate. Drugs such as hydroxychloroquine, which may improve joint involvement, are not used in patients with psoriatic arthritis because their use can worsen skin lesions.

If, despite everything, the involvement progresses, immunosuppressants will be used, such as etanercept, infliximab or adalimumab.

Precautionary measures

There are no preventive measures to avoid psoriatic arthritis. However, it is important to remind patients with psoriasis that it is important that they be attentive to possible joint involvement in order to see their specialist as soon as possible.