What is the pathophysiology of 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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The spondyloarthropathies are chronic inflammatory diseases that most commonly involve the SI joints and the axial skeleton, with hip and shoulder joints less frequently affected. Peripheral joints and entheses and certain extra-articular organs, including the eyes, skin, and cardiovascular system, may be involved to a lesser degree.

The primary pathology of the spondyloarthropathies is enthesitis with chronic inflammation, including CD4+ and CD8+ T lymphocytes and macrophages. Cytokines, particularly tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), are also important in the inflammatory process by leading to inflammation, fibrosis, and ossification at sites of enthesitis. [24, 25, 26] The IL-23/IL-17 axis is also important in the spondyloarthropathies including the induction of Th17 cells and the production of the proinflammatory cytokine IL-17. [27, 28] In addition, TNF-α and IL-17 have been targeted therapeutically for the treatment of axial spondylarthritis.

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