Enthesitis and Enthesopathy Explained

Enthesitis Is a Primary Feature of Spondyloarthritis

Enthesopathy on MRI
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If you have seen the words entheses, enthesitis, or enthesopathy in your x-ray or medical reports, the terminology may have been unfamiliar to you. Let's look at the meaning and also how it relates to various types of arthritis and rheumatic diseases.

  • Enthesis (plural: entheses) typically refers to the connective tissue where tendons, ligaments, or joint capsules attach to bone. Two types of entheses exist: fibrous entheses and fibrocartilaginous entheses. While that is the classic definition, a newer, broader definition suggests that enthesis is more than a simple attachment or insertion site—enthesis functions as a unit which includes adjacent tissues (for example, bone and fibrocartilage connected to synovium). The unit is referred to as the "enthesis organ complex".
  • Enthesopathy is any abnormal condition that affects the entheses (e.g., inflammation of the entheses). Enthesopathy may be due to an inflammatory condition, such as psoriatic arthritis, or a condition related to injury or overload, such as plantar fasciitis.
  • Enthesitis refers to inflammation of the entheses.

Symptoms Associated With Enthesitis

Enthesitis is typically associated with pain, stiffness, and tenderness at the insertion site, sometimes without much swelling. However, where there is involvement of the large insertions of lower limbs, swelling can be significant and prominent. If swelling is absent, enthesitis can be difficult to recognize or suspect during a physical examination. 

Enthesitis is common at the following sites:

  • Achilles tendon
  • Patellar tendon
  • Plantar fascia
  • Elbow epicondyles
  • Knees
  • Vertebrae
  • Iliac crest

Conditions Associated With Enthesitis

Enthesitis may be linked to inflammatory conditions or it may be mechanically induced by injury.

Peripheral enthesitis is characteristic of all of the spondyloarthropathies, including undifferentiated spondyloarthritis, ankylosing spondylitis, psoriatic arthritis, and reactive arthritis

Reactive arthritis is a form of arthritis that results from infection. The swelling of reactive arthritis is often triggered by infection in a more remote body part, such as the urinary tract, intestines or genitals.

Typically the joints of the knees, feet, and ankles are targets for inflammation secondary to reactive arthritis. More specifically, enthesitis in people with reactive arthritis usually occurs in the plantar fascia, pelvic bones or Achilles tendon. Reactive arthritis is actually uncommon and usually goes away in most people within a year after onset.

Ankylosing spondylitis is an inflammatory condition that is most prevalent in men. The inflammation of ankylosing spondylitis affects the vertebrae and causes them to fuse. Chronic enthesitis of the tendons and ligaments of the vertebrae is the first step in the eventual fusion of vertebrae, which is the main feature of ankylosing spondylitis. People with ankylosing spondylitis can also experience enthesitis of the costochondral joints, or joints of the ribs. About 10 percent of people with ankylosing spondylitis also experience enthesitis of the Achilles tendon and plantar aponeurosis (layers of flat, broad, sheetlike tendons). The term plantar aponeurosis refers to the thickened connective tissue that supports the arch of the foot.

Other conditions associated with enthesitis include achilles tendinitis, rheumatoid arthritis, osteoarthritis, and diffuse idiopathic skeletal hyperostosis (DISH).

It may be degenerative enthesopathy that develops with osteoarthritis. The degenerative changes that occur with wear-and-tear osteoarthritis also affect the fibrocartilages.

Imaging Can Help Diagnose Enthesitis

Imaging can help diagnose enthesitis, but the imaging modality utilized depends on whether the axial or peripheral skeleton is affected. MRI is used for the axial skeleton. Ultrasound is preferred for the peripheral skeleton. MRI would again be preferable for any insertions that are inaccessible.

According to Up-To-Date, "Sonographic findings of enthesitis include thickening or intratendinous focal changes of the tendon insertion, edema of the tendon insertion, calcific deposits at the tendon insertion, spurs, erosions, new bone formation, or periosteal changes.

In addition, adjacent bursitis is considered a sign of enthesitis. A positive power Doppler US signal consistent with increased vascularity may be found in active enthesitis."

Treatment of Enthesitis

Treatment of enthesitis is based on the underlying condition. For example, if enthesitis is due to an inflammatory condition, treatment usually focuses on treating the inflammatory polyarthritis. Treatment, in such cases, may include:

Local corticosteroid injections may be utilized if oral medications are inadequate. The biomechanical aspects of enthesitis are also addressed by using insoles and cushions.

Sources:

Bruyn, George AW, MD. PhD. Musculoskeletal Ultrasonography - Clinical Applications. Up-To-Date. Last reviewed February 2017.

Kehl, AS, MD. et al. Enthesitis. Arthritis & Rheumatology. 2016 Feb;68(2): 312-322.

McGonagle D. and Benjamin, M. Entheses, Enthesitis, and Enthesopathy. Arthritis Research Campaign. Topical Reviews. Autumn 2009.

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