Psoriatic Arthritis

Overview

Psoriatic arthritis is an inflammatory joint condition that occurs in some people who have the skin disease psoriasis. It belongs to the spondyloarthritis family and, like the others in that group, can inflame the joints, the tendon attachments, the fingers and toes, and sometimes the spine. It is a long-term condition that tends to flare and settle.

In most people the skin psoriasis appears first, sometimes years before the joints become involved, but in a minority the arthritis comes first or the psoriasis is so mild — hidden in the scalp, behind the ears, or in the nails — that it has gone unnoticed. The severity of the skin disease does not predict the severity of the joint disease; someone with only a small patch of psoriasis can still develop significant arthritis.

Psoriatic arthritis varies more than most types of arthritis in how it presents, from a single swollen finger to widespread joint involvement. Recognising and treating it early protects the joints, because uncontrolled inflammation can, over time, cause lasting damage.

Symptoms

The joint symptoms are pain, swelling and stiffness, which may affect a few joints or many, and may be on one side of the body or both. Stiffness is typically worse in the morning and after rest and eases with movement, reflecting its inflammatory nature.

Two features are especially characteristic. Dactylitis is the swelling of an entire finger or toe so that it resembles a sausage, caused by inflammation of the whole digit. Enthesitis is inflammation where tendons and ligaments attach to bone, most often felt as pain at the back or underside of the heel. Nail changes are common and useful clues — small pits in the nail, or lifting of the nail from its bed.

Some people have inflammatory back and buttock pain from involvement of the spine and sacroiliac joints. The skin psoriasis itself, fatigue, and occasionally eye inflammation can also be part of the picture.

Causes and risk factors

Psoriatic arthritis develops from an overactive immune response, on a background of an inherited tendency. Having psoriasis is the main risk factor, and a family history of psoriasis or psoriatic arthritis increases the likelihood further. Genetic and immune pathways shared with the rest of the spondyloarthritis family underlie the condition.

It is not caused by anything a person did, and it is not contagious. Only a minority of people with psoriasis go on to develop the arthritis, and there is no certain way to predict who will, which is why anyone with psoriasis who develops joint symptoms is worth assessing.

Diagnosis

The diagnosis is made by a rheumatologist from the combination of joint symptoms with the skin and nail findings and a careful examination. There is no single test that confirms it, so the pattern is what matters: the distribution of affected joints, the presence of dactylitis or enthesitis, nail changes, and a personal or family history of psoriasis.

Because psoriatic arthritis can resemble other kinds of arthritis, distinguishing it is important — its treatment and course differ. Where the skin disease is subtle, examining the scalp, nails, and skin folds can reveal the psoriasis that ties the picture together.

Investigations

Blood tests are used mainly to support the picture and to exclude other conditions. Inflammation markers (ESR and CRP) may be raised but are often normal, and the rheumatoid factor test is usually negative — a helpful point in telling psoriatic arthritis apart from rheumatoid arthritis. There is no blood test specific to psoriatic arthritis.

Imaging helps assess the joints and tendon attachments: ultrasound and MRI can show inflammation early, and X-rays reveal any established joint damage. The skin and nails are assessed as part of the whole picture, and where the spine is involved, imaging of the sacroiliac joints may be added.

Treatment

Treatment aims to control inflammation in the joints and, wherever possible, the skin, and to prevent joint damage. For milder joint disease, anti-inflammatory medicines (NSAIDs) may be enough. When more joints are involved, disease-modifying medicines such as methotrexate are used, and these can help the skin as well.

Where the disease remains active, or affects the spine or tendon attachments, biologic and targeted medicines are highly effective. Several act on the same pathways that drive psoriasis — including TNF, IL-17 and IL-23 — so they can treat skin and joints together, which is a real advantage. The choice depends on the pattern of disease, the severity of the skin involvement, and other health factors, and treatment is often coordinated between the rheumatologist and a dermatologist.

Living with psoriatic arthritis

Staying active with regular exercise keeps joints moving and supports the tendons and muscles around them. Keeping to a healthy weight is particularly helpful in psoriatic arthritis — excess weight worsens both the joint and skin disease and can reduce how well some medicines work. Not smoking and caring for the skin are also part of good long-term management.

Because the condition affects skin and joints together, and can involve the eyes and spine, regular review allows the whole picture to be watched and treatment adjusted as needed. With early diagnosis and modern treatment, most people with psoriatic arthritis control both their skin and their joints and lead full, active lives.