Low-dose CT better for detecting progression of bone formation in patients with ankylosing spondylitis

In patients with ankylosing spondylitis (AS), low-density computed tomography (LD-CT) of the whole spine may be a more sensitive method for determining the formation and growth of syndesmophytes compared with conventional radiographs, according to results presented at the Annual European Congress of Rheumatology (EULAR 2017).

The prevalence of AS, caused by chronic inflammation in the spine, is estimated to be 31.9 per 10,000 in North America and 23.8 per 10,000 in Europe.

“Standard dose computed tomography is a sensitive method for assessing structural changes in the spine in patients with AS,” explained lead author Dr. Anoek de Koning, Leiden University Medical Centre, Leiden, Netherlands. “However, its clinical utility has been limited due to its use of relatively high doses of ionizing radiation.”

Dr. Koning and fellow researchers sought to compare the assessment of syndesmophyte formation—or new bony growths—and their growth on conventional radiographs (CR) and LD-CT in patients with AS. They included 50 patients (mean age: 48.6 years; 84% male; 80% HLA-B27) from the Sensitive Imaging of Axial Spondyloarthritis (SIAS) study who met the following criteria:

• modified NY criteria,
• ≥ 1 syndesmophytes on either the cervical and/or lumbar spine on CR, and
• ≥ 1 inflammatory lesion on MRI-spine.

At baseline and again at 2 years, patients underwent conventional radiography of the lateral cervical and lumbar spine, and LD-CT (approximately 2-3 mSV) of the entire spine.

CR and CT were independently assessed by two readers. Images were paired per patient. Readers used mSASSS scoring methods to assess conventional radiographs, and scored syndesmophytes on CT in the coronal and sagittal planes for all “corners” per view (8 corners per vertebral unit).

The two readers scored syndesmophytes as absent (score 0), < 50% of the intervertebral disc height (IVDH) (score 1), ≥ 50% of the IVDH but no bridging (score 2) or as bridging the IVDH (score 3). For each vertebral corner, they calculated the formation of new syndesmophytes (CR score 0 or 1→2 or 3, CT 0→1 or 2 or 3) and growth of existing syndesmophytes (CR score 2→3, CT 1→2 or 3, or 2→3), and the combination of both. CR and CT data were then compared per reader and for the consensus score.

In all comparisons, more patients with progression were detected by CT compared with CR, and this difference was particularly notable in the cases of growth and for cut-offs of a higher number of newly formed or growth of syndesmophytes per patient. A full 30% of patients showed bony proliferation at 3 or more sites on CT, compared with only 6% on CR.

“Our findings support the use of LD-CT as a sensitive method for the assessment of new or growing syndesmophytes in future clinical research without exposing patients to high doses of radiation,” concluded Dr. Koning.