Enthesitis in Psoriatic Arthritis

By Timothy Gower | Updated Aug. 28, 2024

Although you may not have heard of enthesitis, the structures in the body affected by the condition are involved in every move you make. Bones and muscles are held together by tendons and ligaments, which allow them to work together and help all types of movement. The site where a tendon or ligament inserts into a bone is called an enthesis. You have more than 100 entheses in your body.

Enthesitis occurs when an enthesis becomes inflamed. While this painful problem can affect anyone, enthesitis is far more prevalent, and more likely to become chronic, among people with psoriatic arthritis (PsA) and forms of spondyloarthritis, or arthritis that affects the spine. It also occurs with certain types of juvenile idiopathic arthritis.

One in three people with psoriatic arthritis will develop enthesitis. In fact, rheumatologists often look for the presence of enthesitis to help confirm that a patient with joint symptoms has PsA and not another type of arthritis, such as rheumatoid arthritis.

Understanding Enthesitis

Overuse and injury can both cause localized enthesitis. With inflammatory forms of arthritis, the inflammation that drives the disease can cause enthesitis in multiple sites.

Symptoms include pain and stiffness, especially when you move that part of the body. Constant inflammation may promote abnormal bone growth, producing uncomfortable bone spurs (growths that develop on the edge of a bone). And although it isn’t clear why, enthesitis is closely linked to changes in fingernails and toenails, such as pitting and separation from the nail bed, that affect many people with PsA.

Enthesitis is at the root of some common orthopedic problems brought on by overuse, such as tennis elbow.

“However, a person without PsA can apply ice and the enthesitis goes away over time,” says rheumatologist Samantha Shapiro, MD, of UT (University of Texas) Health, Austin. “But in a person with PsA, you have a runaway immune system that continues to inflame the enthesis without normal healing.” That means having psoriatic arthritis sets the stage for the inflammation to become chronic and requires more than ice and time for relief.

Enthesitis often emerges early in the disease process, although it can develop at any stage, says rheumatologist Vivian Bykerk, MD, of Hospital for Special Surgery in New York City. When the condition arises in people with PsA it can affect the elbows, shoulders, hips and knees, among other areas. But one of the most common targets in PsA is where the Achilles tendon attaches to the back of the heel, which can make every footstep a painful experience.

About 40% of people with psoriatic arthritis develop puffy, “sausage-like” fingers and toes, known as dactylitis. This hallmark of PsA “is really a form of enthesitis,” says Dr. Bykerk, because inflammation in the connective tissue of the digits contributes to the swelling.

Diagnosing and Treating Enthesitis

There are no standard lab tests to detect enthesitis. Your doctor may use medical imaging, such as ultrasound, to help determine if you have the condition, but a physical exam along with your medical history and symptoms provide enough information in most cases, says Dr. Shapiro. For example, if you have pain in back of the heel just above the sole of the foot, swollen joints and finger- and toenail pitting, “then that’s enthesitis,” says Dr. Shapiro. “There’s no need for fancy imaging tests.”

Other conditions, such as fibromyalgia, can produce pain in and around the joints, but a simple test of resistance can help identify enthesitis, says Dr. Bykerk. If a patient describes discomfort in the elbow, for instance, she will ask them to raise that arm to test range of motion. If pushing against their palm causes the pain to increase, enthesitis is likely the cause.

“Fibromyalgia tender points won’t have the same level of pain,” says Dr. Bykerk. If your doctor determines you have enthesitis, a change in your treatment plan might be in order.

Disease-modifying drugs like methotrexate and leflunomide are mainstay medications in the treatment of PsA, but they aren’t especially effective at relieving enthesitis, says Dr. Shapiro. As initial therapy for suspected enthesitis, she may try treating a patient with high doses of nonsteroidal anti-inflammatory drugs (NSAIDs), such as naproxen or indomethacin, for up to a month. But NSAIDs are not an option if you have chronic kidney disease and should be limited or avoided if you have a history of gastrointestinal ulcers or bleeding.

If a patient has enthesitis in just one location, Dr. Bykerk will consider injecting a corticosteroid to bring down the inflammation. But if symptoms persist or if enthesitis affects several locations in a person with multiple tender joints, then Drs. Shapiro and Bykerk both agree a biologic drug is likely needed.

The first-choice biologic drug for most patients who need one to manage enthesitis or other PsA symptoms will be a tumor necrosis factor (TNF) inhibitor or interleukin (IL) inhibitor. Janus kinase (JAK) inhibitors and PDE4 blockers may also be the first line of treatment where enthesitis is involved.

If you suspect you have enthesitis, tell your doctor right away. They can help properly diagnose you and come up with a treatment plan to suit your needs.