LAUSR

Abstract Background. The negative metabolic impact of overweight and obesity (OW-OB) on bone health is a matter of concern in pediatrics. This situation is even more delicate in individuals with osteogenesis imperfecta (OI), who already have a compromised skeletal health. Assessing body fat through anthropometric indices in patients with OI is a challenge, mainly in the moderate and severe types, once skeletal deformities disrupt the expected proportionality between weight and height squared as obtained by the classical body mass index (BMI). So, it is asked whether the tri-ponderal mass index -TMI [mas divided by height cubed] would be a better surrogate parameter for adiposity index assessment in this group of patients. Aim. To compare the frequency of OW-OB among patients with moderate and severe forms of OI using both BMI and TMI methods and evaluate impact of each classification on bone fracture rates. Methods. Retrospective study comprised of 32 patients with OI followed at a tertiary level hospital in Brasilia, Brazil. All patients were being treated with intravenous cyclic infusion of disodium pamidronate at the time of evaluation. TMI absolute values and BMI Z-scores were used as indirect measures of adiposity index of patients. OW and OB frequencies in patients with OI were compared with a control group (CG) of 154 non-syndromic children and adolescents. The used TMI thresholds to diagnose OW and OB status were according to: boys, 16.0 kg/m3 and 18.8 kg/m3; girls 16.8 kg/m3 and 19.7 kg/m3, respectively.(1) Results. Thirty-two consecutive individuals (15 females) with OI were studied; mean age at evaluation was 13.4 ± 3.3 years (ranged 7 to 22 years), being 8 patients with OI type I; 11 type III: and 13 type IV. The proportion of OW-OB in OI group (43.8%) was higher than in CG (24.7%) [p = 0.029; Z-score = 2.19]. Using BMI Z-scores, 13 patients (7 females) were classified as overweight and 1 (male) as obese. Using TMI, 2 out of 15 females were classified as OW, and 3 as OB; seven out of 17 males were classified as OW, and 2 as OB. There was no difference in the bone fracture rate observed during the last previous year of follow up when comparing OW-OB and non-OW/OB patients classified according to BMI Z-score (p = 0.13). Nevertheless, after using TMI for classification, a higher fracture rate was observed in the OW-OB group (1.1 per patient-year) compared with the non-OW-OB group (0.4 per patient-year), p = 0.04. Conclusion. Although the proportion of OW-OB patients with OI detected by TMI and BMI were similar, the distribution of OW and OB subgroups was distinct. The finding of a higher fracture rate among the TMI-derived OW-OB individuals in this small sample sized study may suggest that this index would sustain a better characterization than BMI concerning the negative metabolic effect of OW-OB on bone quality among patients with OI. (1) Peterson CM et al. JAMA Pediatr. 2017;171(7):629-636.