Psoriasis and psoriatic arthritis are different diseases, but they are related. Some people may have both at the same time. Some of their causes, symptoms, and treatments are similar.
What Are Psoriasis and Psoriatic Arthritis?
Psoriasis is a skin disease that causes your body to make new skin cells much faster than normal. These cells build up on your skin’s surface. They form thick, scaly, flaky patches called plaques.
Psoriasis plaques can form anywhere on your body. The most common spots are your elbows, knees, lower back, and scalp. Plaques can be large or small, itchy, or even painful.
Psoriasis can also affect your nails. They can become thick, pitted, and crumbly.
Psoriatic arthritis is a type of arthritis that causes pain, swelling, and damage in the joints.
In both conditions, symptoms can flare up and then go away for a while.
Up to 30% of people with psoriasis will get psoriatic arthritis. Most people with psoriatic arthritis have psoriasis for about 10 years before they have joint symptoms. But some people have psoriatic arthritis alone without ever developing the skin symptoms of psoriasis.
Having a severe form of one disease doesn’t mean you’re more likely to get the other disease. You can have severe psoriasis on your skin but never develop psoriatic arthritis. People with severe joint pain from psoriatic arthritis may have only mild skin rashes or none at all.
Overactive Immune System
Psoriasis and psoriatic arthritis are autoimmune diseases. In these conditions, your immune system goes into overdrive. It attacks your tissues instead of only harmful things like bacteria, and viruses. Inflammation, a normal process that your body uses to protect itself, rages out of control.
In psoriasis, that inflammation affects your skin and nails. In psoriatic arthritis, it targets your joints. It can also make you very tired.
Similar Biology
Psoriasis and psoriatic arthritis affect your body in different ways. But deep inside your inflamed tissues, some of the same cells play roles in both diseases.
White blood cells. Inflamed skin, nails, and joints in both diseases may have higher levels of a type of white blood cell called lymphocytes. These include B cells and T cells.
Lymphocytes may also play a role in inflammation in the places where ligaments and tendons attach to your bones. That can happen to people with psoriatic arthritis.
Cytokines. These proteins trigger inflammation. People with both diseases can have high levels of them in their blood and tissues.
In both psoriasis and psoriatic arthritis, a cytokine called tumor necrosis factor alpha, or TNF-alpha, plays a major role. High levels of TNF-alpha can drive inflammation in both your skin and joints.
People with psoriasis or psoriatic arthritis may also have high levels of other cytokines called interleukins (IL).
Blood vessel changes. Another link between these two diseases is that tiny blood vessels in the inflamed skin, nails, or joints may not grow to their normal shape and size. Levels of proteins called growth factors that play a role in how blood vessels grow are high in psoriasis and psoriatic arthritis.
Treatments
Doctors may prescribe some of the same medicines to treat psoriasis and psoriatic arthritis. Drugs that treat both conditions are called systemic treatments. They work throughout your body to treat symptoms in your skin, nails, and joints. You might take these medicines along with other treatments.
Newer treatments called biologics work on an overactive immune system to control inflammation and ease symptoms. There are biologics that treat both psoriasis and psoriatic arthritis.