What is psoriatic arthritis?
Psoriasis is a common, chronic inflammatory skin disease, most often appearing in the form of well demarcated, scaly plaques. It is associated with multiple coexisting conditions. The most prevalent coexisting condition, psoriatic arthritis, develops in up to 30% of patients with psoriasis and is characterised by diverse clinical features often resulting in delayed diagnosis and treatment.
The cause of the psoriasis and the associated arthritis is thought to be a complex interaction of genes and the immune system. Environmental triggers may also play a role, but are difficult to characterise, e.g. stress or viral illness.
Psoriatic arthritis is more common in those with psoriatic involvement of the nails. There is an increased incidence of tendonitis in those with psoriasis. In some, the joint symptoms may be intermittent and in others more persistent.
There are five types of psoriatic arthritis (PsA):
- Symmetric PsA, which may be difficult to differentiate from rheumatoid arthritis
- Asymmetric PsA
- Distal interphalangeal predominant (DIP) PsA, which behave more like osteoarthritis
- Psoriatic spondylitis with involvement of the neck and back
- Arthritis mutilans, which is very rare
What are the symptoms?
Some common symptoms of the condition include swollen joints; stiffness; pain in the muscles and tendons; patches of scaly skin; and swollen fingers and toes. In some cases, patients may experience fatigue, conjunctivitis and uveitis.
Patients who have been diagnosed with spondylitis PsA may feel pain in the spine and experience swelling in the hips, knees, feet, hands, wrists and ankles.
Distal PsA is characterised by swelling in the ends of the fingers and toes, which can cause considerable pain.
How is it diagnosed?
It is necessary to differentiate psoriatic arthritis from rheumatoid arthritis, osteoarthritis, gout, pseudogout, systemic lupus erythematosus, and other forms of spondyloarthritis.
Blood tests may be required to exclude other types of arthritis and to assess any inflammation in the body. Radiology may be helpful in making the diagnosis or excluding other problems.
How can it be treated?
For those with mild disease, anti-inflammatories or joint injections may be adequate, but those with more severe disease require more aggressive therapy.
Significant progress in the last decade or two has resulted in a much better outcome for those with psoriatic arthritis, most notably with the introduction of biologic therapy. Methotrexate or other disease modifying drugs would be used before biologics are considered. The goal is to achieve disease control as soon as possible in order to limit joint damage and to improve quality of life. The advantage of this type of therapy is that both skin and joints tend to improve and quality of life is significantly better in terms of energy and reduced joint damage.