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. Twenty-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. No treatment is provided in the protocol. Treatment with anti-tumor necrosis factor medications is not permitted during the first study year, but there are no other restrictions on the treatments participants may receive.

Reliability of image processing will be tested on repeated measurements of baseline scans. 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.

• INCLUSION CRITERIA:

Twenty-five patients will be studied. Inclusion criteria are:

• Age 18 years or older
• Diagnosis of AS by the modified New York criteria
• Lumbar spine BASRI score of 0, 1, 2, or 3
• Not currently taking or anticipated to receive treatment with anit-TNF alpha medications (etanercept, infliximab, adalimumab) for 1 year

We will aim to recruit at least 6 patients in each of the following BASRI lumbar spine categories:

0 or 1 (normal or suspicious changes)

2 (erosions, sclerosis or squaring with or without syndesmophytes or 2 or fewer vertebrae)

3 (syndesmophytes on 3 or more vertebrae with fusion of at most 2 vetebrae)

EXCLUSION CRITERIA:

• Inability to provide informed consent.
• BASRI lumbar spine score of 4 (complete fusion; 12)
• Current or anticipated imminent treatment with anti-TNF alpha medications
• Contraindication to MRI scanning based on the NMR Center MRI Safety Screening Questionnaire or size or weight limitations of the scanner.
• History of allergic reactions to gadolinium-DPTA contrast used for MRI
• Anticipated unavailability for follow-up over 2 years
• Pregnancy
• Onset of AS at age 16 or younger
• Spondyloarthropathy other than AS