A Comment on ‘Changes in Bone Mineral Density in Women Following 1-year Gastric Bypass Surgery’ Published by Casagrande DS et al.

Abstract

Sirs,In a recent issue of Obesity Surgery, a study on longitudinalchanges in bone mineral density (BMD) after gastric bypasssurgery [1] was published. The authors presented severallaboratory data and BMD measurements at the spine andproximal femur at baseline and follow-up. Generally,both laboratory variables and BMD results have changedsignificantly. However, we have comments concerningmethodology of BMD measurements and the way of theirpresentation.Firstly, in a description of densitometry, the authors didnot provide a precision expressed as coefficient of variation(CV%). This information is especially important in a longi-tudinal observation. In each densitometry unit, serial mea-surements should be performed and CV% should beestablished. Moreover, in a prospective study, it is necessaryto calculate the value of the least significant change (LSC)using a common formula: RMS_CV×2×1.41. The use ofLSC allows to establish whether the BMD change in anindividual subject exceed the value of LSC.The authors presented changes in BMD only as meanexpressed in percent. Such way of presentation does notexpress real bone changes in a satisfactory manner. Onemay expect that due to precision error BMD change not ineach patient will exceed the value of LSC. In our recentstudy, we performed measurements in 29 women after lapa-roscopic sleeve gastrectomy, and after 6 months, BMD havedecreased for femoral neck, total hip and spine by 1.24, 6.99and 5.18 %, respectively [2]. We also performed an analysisof changes in individual patients using LSC, and such wayallowstoestablishthatchangeinBMDwasnotpresentinallpatients. For spine, BMD decreased only in 38 % of allwomen, andin three of them BMD even increased. In regardto femoral neck BMD, real decrease was noted in 72 %, andfor total hip BMD, a decrease exceeding the value of LSCwas observed in 82 % of all subjects studied. For hip densi-tometric measurements, an increase was not noted but insome women a decrease was not present.Our analysis confirms that we should not expect thepresence of significant bone changes in all subjects aftersurgical method of treatment of obesity. We recommend forauthorsofthecommentedstudytopresentsuchdatathatwillhelpinbetterunderstandingofbonechangesinsubjectsaftersurgical obesity management.References