What is peripheral enthesitis and how does it progress in ankylosing spondylitis (AS) and undifferentiated spondyloarthropathy (USpA)?

Updated: Feb 02, 2021
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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Peripheral musculoskeletal involvement occurs in 30-50% of all patients. Peripheral enthesitis is the basic pathologic process, involving inflammation at the site of insertion of ligaments and tendons on to bone. This often progresses from erosion and osteitis to ossification, resulting in telltale radiological signs of periosteal new bone formation.

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