Up to 30% of people with psoriasis will develop psoriatic arthritis, an autoimmune disease that can lead to pain, swelling, and stiffness in the joints. Psoriatic arthritis is generally divided into five subtypes, depending on which joints are affected and how many. But the system isn’t perfect. For instance, the five types don't take into account symptoms such as dactylitis (when the fingers and toes swell into sausages) and enthesitis (inflammation of areas near the tendons and ligaments). You can also have one type of psoriatic arthritis initially only to develop a different type later on. Still, says Namrata Singh, MD, clinical assistant professor of medicine at the University of Iowa Carver School of Medicine, the types provide a good "bird’s eye view" of the condition and can also help guide therapy. Here, the five forms of psoriatic arthritis patients should know about.
RELATED: 10 Psoriatic Arthritis Symptoms
Asymmetric oligoarticular psoriatic arthritis (sometimes referred to as simply asymmetric psoriatic arthritis) affects about a third of people with the condition. It’s "asymmetric" because a joint on one side of the body can be affected while the mirror-image joint on the other side remains healthy. Although this type can affect any part of the body, it usually impacts no more than four or five joints.
Also known as symmetric psoriatic arthritis, this is the most common form of the condition and accounts for about half of all cases. This type is "symmetric" because it affects the same joint on both sides of the body, much like rheumatoid arthritis. It usually impacts five or more joints which, again, can be anywhere on the body.
Distal interphalangeal predominant
About 20% of psoriatic arthritis cases involve the body’s distal interphalangeal joints, meaning those at the ends of the toes and fingers. Because these joints are closest to the nails, symptoms can include nail changes such as spotting, pitting, or separating from the nail bed.
In spondylitis, inflammation reaches the spine, causing stiffness as well as pain and difficulty moving the neck, lower back, and sacroiliac joints, which are the joints between the sacrum (the bone that supports the spine and is connected to your tailbone) and the pelvis. This type can also affect joints in the arms, legs, hands, and feet.
The most severe form of psoriatic arthritis, arthritis mutilans accounts for about 5% of cases and can seriously damage the joints in the hands and feet. Over time, it can lead to "telescoping" of the digits, when the fingers and toes become shorter, and can also contribute to bone loss. "Hopefully, we are seeing less and less [arthritis mutilans] because therapies are working well," says Dr. Singh.