Dynamics of syndesmophyte growth in AS as measured by quantitative CT: heterogeneity within and among vertebral disc spaces.
OBJECTIVE
Syndesmophytes in AS typically grow slowly, but it is not known whether growth is uniform among syndesmophytes in the same intervertebral disc space (IDS) or among different IDSs in the same patient or if growth is heterogeneous. We examined the dynamics of syndesmophyte growth over 24 months using CT, with the main aim of determining if syndesmophytes in the same IDS or the same patient grow at similar rates.


METHODS
We performed lumbar spine CT scans on 33 patients and measured syndesmophytes in four IDSs using a validated computer algorithm. Scans were done at baseline and 12 and 24 months. We compared absolute and percentage changes in volume from baseline to 12 months and to 24 months among syndesmophytes in the same IDS and among four IDSs of each patient. We also examined whether growth among all IDSs differed between study years.


RESULTS
Among 60 IDSs with at least two syndesmophytes at baseline (range 2-6), there was substantial heterogeneity in both absolute (P < 0.0001) and percentage (P = 0.0002) volume increases among syndesmophytes in the same IDS. Several IDSs had both syndesmophytes with no growth and syndesmophytes that increased by >100 mm(3). Similarly there was significant heterogeneity in syndesmophyte growth among IDSs of individual patients. Increases in total syndesmophyte volume for each patient also tended to differ between study years (P = 0.07).


CONCLUSIONS
Syndesmophytes in AS do not all grow continuously. Rates of growth over 24 months commonly differ between syndesmophytes in the same IDS and between different IDSs in the same patient, suggesting that local factors regulate syndesmophyte growth.
National Institute of Arthritis and Musculoskeletal and Skin Diseases, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda and Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Sovira
S
Tan
National Institute of Arthritis and Musculoskeletal and Skin Diseases, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda and Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Jianhua
J
Yao
National Institute of Arthritis and Musculoskeletal and Skin Diseases, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda and Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
John A
JA
Flynn
National Institute of Arthritis and Musculoskeletal and Skin Diseases, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda and Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Lawrence
L
Yao
National Institute of Arthritis and Musculoskeletal and Skin Diseases, Radiology and Imaging Sciences, Clinical Center, National Institutes of Health, Bethesda and Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, MD, USA wardm1@mail.nih.gov.
Michael M
MM
Ward
D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging* / Q000254:growth & development; D008137:Longitudinal Studies; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging* / Q000254:growth & development; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013167:Spondylitis, Ankylosing / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging* / Q000254:growth & development; D014057:Tomography, X-Ray Computed / Q000379:methods
ankylosing spondylitis; computed tomography; syndesmophyte