Enthesitis

• 'Enthesitis' is the term used to describe inflammation at tendon, ligament or joint capsule insertions
  • thus applies to disease associated with the spondyloarthritides (SpA) including ankylosing spondylitis, psoriatic arthritis, reactive arthritis and undifferentiated SpA
  • term 'enthesopathy', however, has a wider meaning and designates all pathological abnormalities of insertions including inflammatory changes and degenerative problems
  • enthesitis may manifest as pain, protracted stiffness and prominent swelling of large insertions, including those of the Achilles and patellar tendons
    
    
• Entheses
  • there are two types of enthesis: fibrous and fibrocartilaginous
    • fibrous tissue of the tendon or ligament extends all the way up to the bone, but at the latter there is a small plug of fibrocartilage at the attachment site itself
    • most entheses of rheumatological significance are fibrocartilaginous
      • presence of this tissue at an enthesis stiffens the tendon/ligament and thus helps to create a more gradual change in mechanical properties between soft and hard tissues
      • especially an enthesis ensures that any bending of the tendon/ligament fibres during joint movements is spread gently away from the bone - thus dissipating stress concentration
        
        
• when is enthesitis inflammatory and when is it mechanically induced?
  • mechanically-related tendinopathy or enthesopathy may occur from injury, including sports-related activity. Imaging studies may confirm the presence of entheseal pathology but the appearances, whether at the annulus or bone-disc interfaces in the spine or the plantar fascia, may be similar in both mechanical and inflammatory disease
    • in the case of the Achilles tendon, degenerative tendon disease typically occurs 2-6 cm proximal to the enthesis itself, whereas inflammatory disease is based around the insertion and adjacent bone
    • both inflammatory and degenerative enthesopathy share common features
      • entheses are sites of high mechanical stressing and with age normal entheses are subject to wear and tear; thus degenerative changes occur at their fibrocartilages that are similar to those seen in osteoarthritic articular cartilage
        
        
• imaging in enthesitis
  • if axial skeleton enthesitis is suspected then MRI is the modality of choice
  • if peripheral skeleton enthesitis is suspected then ultrasound is the preferred method
    • for some synovial joints, including the hip and knee, where the insertions (including those of the cruciate ligaments) may be inaccessible to the probe, MRI is the test of choice
      
      
• treatment of inflammatory enthesitis
  • reduction of biomechanical stresses by such means as insoles and cushioning should be used where appropriate
  • local corticosteroid injections often help if anti-inflammatory agents fail to alleviate pain associated with isolated enthesitis
  • for isolated severe inflammatory enthesitis with soft tissue swelling, anti-TNF agents have been shown to be effective in case series - however, use of biologic therapies within the UK health service and elsewhere is restricted and there are currently no specific guidelines for the use of these agents for isolated enthesitis
  • in the past local radiotherapy has been used with some success, especially with disabling heel enthesitis
  • often, treatment of inflammatory enthesitis is simply part of the treatment of an associated polyarthritis where agents including sulfasalazine and methotrexate are used

Reference:

• 1) Arthritis Research Campaign (2009). Topical Review - Entheses, enthesitis and enthesopathy.