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

Updated: Sep 03, 2019
  • 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. See the image below. The outcome in patients with a spondyloarthropathy, including AS, is generally good compared with that in patients with a disease such as rheumatoid arthritis. 

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 clinical features of AS but with normal plain radiographs of the sacroiliac joints and spin. This disorder 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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