Authors: Stella Maris Fabiane Kirsten J Ward James C Iatridis Frances M K Williams
Publish Date: 2016/06/06
Volume: 25, Issue: 9, Pages: 2716-2720
Abstract
Twin volunteers from the TwinsUK cohort having spine magnetic resonance MR scans coded for LDD and information about T2D were investigated in two ways First as a population sample and second as a cotwin case control study in twin pairs discordant for T2D Other risk factors for LDD considered were age bodymass index BMI smoking and alcoholIn 956 twin volunteers T2D had a prevalence of 66 LDD score was higher in T2D twins 149 vs 131 p = 004 but was not an independent risk factor if the influence of age and BMI were included in the model Discordant twin analysis n = 33 pairs showed no significant difference in LDD between twins having T2D and their unaffected cotwinsTwins having T2D did manifest higher LDD scores but the effect was abrogated once BMI was included in multivariable analysis showing it is not an independent risk factor for LDD The population study had 80 power at 01 significance level to detect a difference of 18 in LDD score range of 0–60 so if there is an effect of T2D on LDD it is likely to be smallLow back pain is highly prevalent in the Western world and accounts for considerable work absenteeism There is an accepted relationship between back pain and lumbar disc degeneration LDD although the strength of the association remains debated 1 2 There is some evidence that type 2 diabetes mellitus T2D is important in the aetiology of LDD T2D is reported to be associated with spinal stenosis 3 Individuals with obesity and T2D are at an increased risk of low back pain and musculoskeletal complications but the relative contributions of the two risk factors remains unclear 4 5Worldwide prevalence of diabetes mellitus in general is 9 of the population with T2D accounting for 90 of all the cases Increased bodymass index BMI is one of the most important risk factors for T2D and an epidemic of obesity is leading to increased T2D prevalence This has important implications for low back pain and disability which already represent considerable social challenges Changes in intervertebral disc physiology and structure in diabetes are well documented in animal models 6 7 and in vitro studies of disc cells in high glucose media support a deleterious effect Increased BMI is also a wellrecognised risk factor for LDD 5 8 although the strength of this association has been disputed 9A population based study of LDD epidemiology accounting for T2D has not yet been described perhaps because of the considerable heritability of LDD 70 of the phenotypic variance in LDD is genetic This means that there is considerable genetic influence on LDD phenotype variation so large population samples are required for adequate power The inherent genetic matching of twin pairs provides a powerful study design and in TwinsUK an unselected sample of twins have had LDD determined using the gold standard method of T2weighted MR scansTwinsUK is a large registry of samesex twins containing both monozygotic MZ and dizygotic DZ same sex twin pairs It contains extensive genotype and phenotype data obtained at clinical visits and by questionnaire TwinsUK has contributed to the understanding of a wide variety of traits and diseases including musculoskeletal disease and LDD and they are similar to the general singleton population 2 10 11 We examined the association between LDD and T2D status of twins having baseline lumbar spine MRI scans 10 as a population sample In addition we considered the twin pairs in a T2D discordant cotwin design using the inherent matching within twin pairs for age sex genetic factors 100 in monozygotic MZ and on average 50 in dizygotic DZ twin pairs and other measured and unmeasured confounders MR scans had been scored for LDD and the summary measure of disc degeneration LDD score was made considering four features disc height disc signal intensity disc bulge and anterior osteophytes each coded 0–3 and summed over five discs 10 T2D was defined by the serum fasting glucose level ≥7 mmol l−1 and/or selfreport of a physician’s diagnosis of T2D on questionnaire as previously 12 Other risk factors for LDD considered were age body mass index smoking alcohol consumption and glycated haemoglobin HbA1C mmol−1 Ethics permission had been obtained from the St Thomas’ Hospital ethics committee and twins gave fully informed written consent
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