What is the disease progression of ankylosing spondylitis (AS)?

Updated: Feb 02, 2021
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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The initial presentation of AS generally relates to the SI joints; involvement of the SI joints is required to establish the diagnosis. SI joint involvement is followed by involvement of the discovertebral, apophyseal, costovertebral, and costotransverse joints and the paravertebral ligaments.

Early lesions include subchondral granulation tissue that erodes the joint and is replaced gradually by fibrocartilage and then ossification. This occurs in ligamentous and capsular attachment sites to bone and is called enthesitis. [29]

In the spine, this initial process occurs at the junction of the vertebrae and the annulus fibrosus of the intervertebral discs. The outer fibers of the discs eventually undergo ossification to form syndesmophytes. The condition progresses to the characteristic bamboo spine appearance.

Extra-articular involvement can include acute anterior uveitis and aortitis. Anterior uveitis occurs in 25-30% of patients and generally is acute and unilateral. Symptoms include pain, lacrimation, photophobia, and blurred vision. Cardiac involvement, including aortic insufficiency and conduction defects, is generally a late finding and is rare. [30]

Pulmonary involvement is secondary to inflammation of the costovertebral and costotransverse joints, which limits chest wall range of motion (ROM). Pulmonary fibrosis is generally an asymptomatic incidental radiographic finding. Neurologic deficits are secondary to spinal fracture or cauda equina syndrome resulting from spinal stenosis. Spinal fracture is most common in the cervical spine.

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