Progression of Spinal Fusion in Ankylosing Spondylitis

Spinal fusion is the clinical, radiological, and pathological hallmark of ankylosing spondylitis (AS). However, spinal fusion occurs slowly in AS. Serial radiographs rarely show changes over 2 years, and often 5 or more years are needed to demonstrate progression of spinal fusion. Methods that are more sensitive to changes in the extent of spinal fusion than plain radiographs are needed to test if any treatments can slow or halt spinal fusion in AS. The need for an improved measure of spinal fusion is heightened now that several new medications are available that have the potential to markedly decrease spinal inflammation in AS. The goal of this pilot study is to test whether measurement of bone mineral density, bone volume, or bone mass at the annulus fibrosis of lumbar disc spaces by computed tomography (CT) can provide a reliable, valid, and sensitive measure of spinal fusion in patients with AS. Fifty-five participants will have lumbar spine CT scans at baseline, 12 months, and 24 months, lumbar spine magnetic resonance imaging at baseline and 12 months, and spinal radiographs at baseline, 12 months, 24 months, and 48 months. In addition, clinical assessments will be done every 4 months during the first 24 months. An option to perform only the baseline studies is also possible. No treatment is provided in the protocol. Reliability of image processing will be tested on repeated measurements of baseline scans. Reliability will also be assessed with repeat CT scans on up to 10 participants. Construct validity will be tested by correlation of CT measures with scores of plain radiographs, lumbar magnetic resonance imaging, and spinal range of motion. The sensitivity to change of the CT measures over 12 months and 24 months will be compared to those of two scoring systems based on plain radiographs.