Psoriatic arthritis and psoriasis: What's the connection?
What is the connection between psoriasis and psoriatic arthritis? Both are thought to be caused primarily by the immune system. However, not everyone who has psoriasis, which causes patches or plaques of scaly and inflamed skin, develops psoriatic arthritis. This form of inflammatory arthritis causes joint swelling and pain, and may lead to permanent deformity and damage if not treated.
Symptoms of psoriatic arthritis
Some of the most common psoriatic arthritis symptoms include:
- Painful, swollen joints. Psoriatic arthritis can be symmetrical (meaning it affects the same joints on both sides of the body) or asymmetrical. With asymmetrical psoriatic arthritis your left fingers and right toes might be affected, for example.
- Sausage-like swelling of fingers and toes.
- Nail changes. Psoriatic arthritis often affects the joints closest to the nail bed. It can cause pitting or ridging of the nails or nails that peel away from the fingers and toes.
- Back and neck pain. For about 5% of people with psoriatic arthritis the main symptom is an inflamed spinal column, which makes movement very difficult.
- Stiffness, especially after sitting or sleeping.
How psoriasis and psoriatic arthritis are connected
Psoriasis affects between 2% and 3% of the UK population, and approximately 10% of people with psoriasis will develop psoriatic arthritis. In most cases the skin symptoms of psoriasis appear before psoriatic arthritis develops. However it is possible for psoriatic arthritis symptoms to appear months, or even years, before any skin lesions develop.
Both psoriasis and psoriatic arthritis are thought to be caused primarily by your immune system. In the case of your skin it causes cells to grow too quickly without sloughing off. Layers of skin build up, resulting in the skin plaques of psoriasis. With psoriatic arthritis the immune system targets joints and connective tissue, causing destructive, painful, swollen joints.
There does not seem to be a connection between where the scaly skin patches from psoriasis are located and which joints are affected by psoriatic arthritis. For example you can have skin lesions on both your elbows, but your elbow joints can be unaffected by psoriatic arthritis. In the same way psoriatic arthritis can cause sausage-like swelling of the toes without any redness or scaling on the feet.
Psoriasis skin lesions can flare up and then subside, and psoriatic arthritis symptoms may also wax and wane. However, while psoriasis does not cause scarring or any other permanent damage to the skin, psoriatic arthritis can cause permanent deformity and damage to the joints if not treated. That is why it is very important to work with your doctor even if your psoriatic arthritis symptoms subside. Don't decrease or change your medications without talking to your doctor first.
Both psoriasis and psoriatic arthritis seem to have a strong genetic component. About 40% of people who develop psoriatic arthritis have relatives with either psoriasis or psoriatic arthritis. Family members of people with psoriatic arthritis are 55 times more likely to develop the disease than those without a family history of the disease. While scientists don't yet know which genes are responsible for psoriasis and psoriatic arthritis, research is underway to find the genetic markers. Discovering which genes are involved in psoriatic arthritis may help scientists develop future treatments.
Genetics is not the only factor in determining whether someone develops psoriasis and psoriatic arthritis. Environmental factors are also believed to be very important.