Psoriatic arthritis (PsA) is a type of inflammatory arthritis that occurs in people who also have the skin condition psoriasis.
Psoriasis is a common auto-immune skin disease which affects around 5% of the population. It can present in many different ways but most often is a red, scaly rash on the elbows and knees. Sometimes it is on the trunk or scalp, or may be accompanied by nail changes.
Psoriatic arthritis (PsA) is similarly an auto-immune disease, meaning it occurs when the body’s immune system becomes unable to recognise its own tissues (self from non-self) and starts to attack healthy tissue.
In PsA, this causes joint pain, swelling and other symptoms relating to inflammation.
Psoriatic arthritis occurs in up to 30% of people who have psoriasis. Usually, the psoriasis precedes the arthritis but in about 15% of cases the arthritis starts first.
Psoriasis can occur at any age but Psoriatic Arthritis (PsA) typically starts in the 30 – 50+ age group, affecting men and women equally.
The most common presentation of Psoriatic Arthritis is pain, stiffness and swelling in and around the joints in a person with known psoriasis. If the person does not yet have psoriasis, the diagnosis may be harder and sometimes the only clue is a family history of psoriasis.
Like other types of inflammatory arthritis, Psoriatic Arthritis is ‘systemic’ meaning it can affect many joints and involve other parts of the body. The disease pattern is very variable with exacerbations (increases in disease activity called flares) and quieter periods. It may affect just one, two or many joints and may be mild or severe.
Symptoms and Signs
Psoriatic skin plaques are usually red, itchy and scaly and may be very small or widespread. Nail abnormalities including pitting, flaking and discolouration are strongly associated with arthritis.
Arthritis may affect one or many joints:
Spondylitis – Pain and stiffness in neck, back or buttocks is caused by spinal inflammation. Other features include morning stiffness and difficulty with prolonged sitting.
Enthesitis – describes inflammation where tendons attach to bones. Common sites are the heels, elbows, knees and hips.
Dactylitis – means a swollen finger or toe (‘sausage finger’) and is caused by inflammation affecting joints and tendons in the digit.
An underappreciated (and common) symptom of inflammatory arthritis is not well understood but activity of the disease, chronic pain and emotional effects all contribute.
Infrequent inflammation of the eye tissues causes redness and pain (uveitis or iritis). Early treatment prevents long term damage. Bloody diarrhoea or bowel symptoms could indicate associated colitis (inflammation in the bowel).
Other Associations (co-morbidities)
People with psoriatic arthritis may be at increased risk of heart disease or stroke; medications and lifestyle changes can decrease this risk.
What causes Psoriatic Arthritis?
The exact cause of psoriatic arthritis is unknown. However, a combination of genetic, immunologic and environmental factors all play a part.
Research suggests that something, perhaps an infection, may trigger psoriatic arthritis. No specific infection has been identified but it has been suggested that bacteria in patches of psoriasis may trigger the arthritis.
There is a strong genetic association and often other members of the family may have psoriasis or psoriatic arthritis. People who are overweight are more at risk of developing both psoriasis and psoriatic arthritis.
Psoriatic arthritis is diagnosed by a combination of clinical examination, medical history, blood and other tests such as x-rays. Sometimes the diagnosis is clear but it may be confused with other forms of arthritis, such as rheumatoid or osteoarthritis. It is advisable to be seen by a rheumatologist who can diagnose, manage and coordinate treatment with a dermatologist, GP and other members of the health care team.
Psoriatic arthritis is treated according to severity, with medications and lifestyle changes to help both skin and joints. This may include treatment of pain and stiffness with medication to control inflammation.
The skin and joint conditions arise independently but drug treatment for the arthritis often helps psoriasis.
Becoming involved in your health care will help you manage your condition. Simple exercises such as daily walking can help stiffness and promote weight loss.
Recent advances in the treatment of Psoriasis and PsA have greatly improved the outcome for people with either or both of these conditions. Early diagnosis and specialist assessment to discuss options is strongly recommended.
by Dr Nicola Cook MRCP FRACP (Rheumatologist)