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lunes, 24 de enero de 2011

Twin spine study: Genes and lumbar disc degeneration influence low back pain



 

Frances MK. Williams

VIENNA — From their study of disc degeneration and low back pain in female twins in the TwinsUK register, investigators at King’s College London concluded that lumbar disc degeneration and genetics are the main factors responsible for low back pain among women.

“To summarize our results, predisposition is the main risk factor for low back pain (LBP), and lumbar LBP is strongly based on the extent of lumbar disc degeneration,” Frances MK. Williams, PhD, FRCP(Edin), said at the 2010 Annual Congress of the Spine Society of Europe (EuroSpine 2010), held here.

Williams is head spine unit within the department of twin research and genetic epidemiology unit at King’s College London. Her colleague Gregory Livshits, PhD, the study’s first author, conducted the analysis and Maria Popham, MSc, coded the MRIs.

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Livshits’ work factored in information from 908 unselected twins’ (ages 32 to 72 years) sagittal T2-weighted lumbar spine MRI scans, from among 378 and 716 monozygotic (MZ) and dizygotic pairs, respectively, that were recruited from the TwinsUK register for inclusion in the cross-sectional study.

Other variables they studied were the twins’ age, weight, smoking status, manual work, hip bone mineral density (BMD) and exercise status.

Staged analysis

Investigators determined the amount of disc degeneration on sagittal T2-weighted MRIs by scoring MRI features typically associated with lumbar disc degeneration: disc signal, disc height, disc extension into the canal and presence of anterior osteophytes. They correlated the MRI scores with LBP ratings obtained from questionnaires and interviews. LBP was defined as site-specific pain lasting more than 1 month, which makes daily activities impossible to perform.

Sagittal T2-weighted MRI
Sagittal T2-weighted MRI shows one twin’s spine at the outset of the study. Investigators rated four main disc traits to convey the amount of lumbar disc degeneration seen.

Lumbar MRI taken at a follow-up
Lumbar MRI taken at a follow-up visit provided added information about any lumbar disc degeneration progression.

Images: Popham M

Statistical analysis was performed in stages, doing a multi-logistic regression analysis and other analyses specifically for lumbar disc degeneration and LBP, Williams said.

Based on the analysis, smoking was the only factor that was not statistically different between the groups, she said.

Independent factors analyzed

Williams and colleagues noted in the abstract that they found a similar LBP rate (24.2%) in both types of twins, but the concordance was higher among the MZ twins.

“This therefore shows that there were genetic factors that had an influence,” Williams said.

Independently, hip BMD and amount of exercise significantly contributed to LBP prevalence, while age, weight, smoking status and manual work did not, “although they had a significant independent effect on lumbar disc degeneration,” as was noted in the abstract.

Based on their ongoing study of the relationship between BMD in the lumbar spine and degenerate discs, “There is a clear association between BMD at the lumbar spine and degenerate discs, which begs the question, of course, which comes first?” Williams said. “We feel the evidence from the hip, which is very much mirroring what you see at the lumbar spine, suggests that the relationship is the other way around … . These people have an inherited predisposition to raised BMD, to be bone formers, if you like, than bone losers, and this perhaps impacts on their disc degeneration,” – by Susan M. Rapp

Reference:
  • Livshits G. Ann Rheum Dis. 2010;60: 2102-2106.
  • Livshits G, et al. Lumbar disc degeneration and genetic factors are the main risk factors for low back pain: the UK Twin Spine Study. Paper #56. Presented at EuroSpine 2010. Sept. 15-17, 2010. Vienna.

 

  • Frances MK. Williams, PhD, FRCP(Edin), can be reached at the Department of Twin Research and Genetic Epidemiology, King’s College London, St. Thomas’ Hospital, London SE1 7EH, UK; e-mail: frances.williams@kcl.ac.uk.
  • Disclosure: The study was funded by the Wellcome Trust and Arthritis Research UK.

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