Psoriatic arthritis, or PsA, is an inflammatory type of arthritis, which sets it apart from the more traditional and well-known osteoarthritis. PsA is a chronic and autoimmune disease, meaning it’s caused by an overactive immune system that attacks healthy, normal cells in the body.
With PsA, “your joints get enlarged and restricted and stiff, and there’s inflammation in the joint space, as opposed to a bone-on-bone arthritis, or osteoarthritis, where you lose the joint space,” says Nicola Kim Berman, MD, a rheumatologist based in New York. (Learn more about symptoms of psoriatic arthritis here.)
PsA can be categorized into different types based on which joints are affected, but the types aren’t necessarily distinct. “It is possible to have multiple types of psoriatic arthritis,” says Dr. Berman. “At different points in time, you could have swelling of your knee, and then you could have back pain, and then, later on, you could develop some pain in your hands—or it could present similarly at the same time.”
There are seven main types of psoriatic arthritis:
Distal psoriatic arthritis primarily affects the distal joints, which are the last joints at the ends of fingers and toes. People with this type of PsA are likely to experience nail changes in their fingernails and toenails.
Dactylitis is the swelling of small joints and tendons that affect individual fingers or toes.
Symmetric psoriatic arthritis affects joints on both sides of the body. For example, if you are having joint pain in your right wrist, you probably have it in your left wrist, too. This is the most common type of PsA and accounts for about half of PsA diagnoses.
Asymmetric psoriatic arthritis (also called oligoarticular PsA) does not equally affect both sides of the body. You might have joint pain in your right wrist but not your left wrist. This is another common type of PsA and accounts for about 35 percent of PsA diagnoses.
Enthesis causes inflammation in ligaments and tendons, most commonly the Achilles tendon.
Spondylitis causes pain and stiffness in the spinal column: the spine, neck, lower back, and sacroiliac joints (which connect the spine to the hips). Spondylitis affects 20 percent of people with PsA. If inflammation goes untreated, psoriatic spondylitis can progress to ankylosing spondylitis—when the vertebrae fuse together and the spnie becomes immobile.
Arthritis mutilans is the most severe type of PsA, but it’s also less common: It accounts for just 5 percent of PsA diagnoses. This type of PsA causes damage and deformities to the joints, especially the fingers and toes. “That’s a rapidly destructive form of arthritis that leads to deformities quite quickly,” says Dr. Berman.
Treating PsA takes several factors into account, including the type of PsA. For example, since some types are more severe—such as arthritis mutilans—they may require more aggressive treatment options.
“There’s been a lot of advances in psoriatic arthritis, and our ability to treat these conditions has very much so changed for the better in the last couple of years,” says Dr. Berman. “There’s a very promising trajectory for our treatments for psoriatic arthritis.”