What are ankylosing spondylitis (AS) and undifferentiated spondyloarthropathy (USpA)?

Updated: Jul 17, 2018
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

Ankylosing spondylitis (AS), a spondyloarthropathy, is a chronic, multisystem inflammatory disorder involving primarily the sacroiliac (SI) joints and the axial skeleton. The outcome in patients with a spondyloarthropathy, including AS, is generally good compared with that in patients with a disease such as rheumatoid arthritis. See the image below.

Anteroposterior radiograph of sacroiliac joint of Anteroposterior radiograph of sacroiliac joint of patient with ankylosing spondylitis. Bilateral sacroiliitis with sclerosis can be observed.

Non radiographic axial spondyloarthropathy is a term used to describe patients with predominantly axial features and includes patients with clincal features of AS but with normal plain radiographs of the sacroiliac joints and spine and probably represents an earlier phase or milder form of AS.

Undifferentiated spondyloarthropathy (USpA) is used to describe patients with predominantly peripheral features and may represent an early phase or incomplete form of AS or another spondyloarthropathy.


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