How is inflammatory back pain affect characterized in ankylosing spondylitis (AS)?

Updated: Feb 02, 2021
  • Author: Lawrence H Brent, MD; Chief Editor: Herbert S Diamond, MD  more...
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Inflammatory back pain is the most common symptom and the first manifestation in approximately 75% of patients. [75] The pain is typically dull and poorly localized to the gluteal and sacroiliac (SI) areas.

Symptoms associated with inflammatory back pain include insidious onset occurring over months or years, generally with at least 3 months of symptoms before presentation. Most patients have mild chronic disease or intermittent flares with periods of remission. The spinal disease is rarely persistently active.

The pain often begins unilaterally and intermittently, and generally begins in the lumbosacral region (SI joints). However, as the disease progresses, it becomes more persistent and bilateral and progresses more proximally, [5] with ossification of the annulus fibrosus that results in fusion of the spine (bamboo spine).

Patients commonly experience morning stiffness lasting at least 30 minutes, improvement of symptoms with moderate physical activity, and diffuse nonspecific radiation of pain into both buttocks. Patients often experience stiffness and pain that awakens them in the early morning, a distinctive symptom not generally found in patients with mechanical back pain.

Diagnostic criteria for inflammatory back pain have been proposed. [76, 77] When 4 of the 5 following criteria are present, it yields a sensitivity of 79.6% and a specificity of 72.4% [77] :

  • Improvement with exercise
  • Pain at night
  • Insidious onset
  • Age of onset less than 40 years
  • No improvement with rest

In contrast, acute onset of pain, exacerbation of symptoms with activity, and radicular radiation of pain suggest a mechanical or degenerative process such as disc disease.

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