Relationship between body mass index and functional recovery in stroke rehabilitation setting

Sir, Recently, Kalichman et al. reported in Disability and Rehabilitation that the body mass index (BMI) measured at admission to a rehabilitation center was negatively correlated with changes in the Functional Independence Measure (FIM) score (delta-FIM) among patients with stroke. [1] These findings intrigued us because weight management for obese patients with stroke remains an important issue in stroke rehabilitation settings, and because our previous research,[2] which had focused on BMI and delta-FIM, led to a conclusion different from that reported by Kalichman et al. Whether a high BMI is beneficial or harmful for the functional recovery during the rehabilitation of patients with stroke has not been proven yet. [2–6] In this letter, we would like to discuss some concerns regarding the study. First, the length of hospital stay and pre-stroke functional ability were not included in the linear regression analysis of FIM at discharge. The length of stay may be a confounder for FIM at discharge because a significant correlation between the length of stay and FIM at discharge was shown in this study [1] and in a previous article. [2] Even if the authors of the current study recruited patients with a first-ever stroke, pre-stroke functional ability, which is affected by various diseases (e.g. cardiovascular diseases, cognitive impairment and others), it is also a strong predictor of functional recovery. [2,3] Therefore, these variables should have been included in the multiple regression analysis. Second, the relationship between BMI and delta-FIM may be disputable if patients with BMI >40 kg/m were excluded. BMI (as continuous variable) and delta-FIM showed a weak relationship (rho1⁄4 0.20, p1⁄4 0.045). Moreover, considering the mean BMI of 28.45 6 5.54 kg/m that was reported in the study, the values of BMI >39.53 kg/m (five plots) would be considered as outliers, if an outlier was defined as the one which is outside the two standard deviations. The relationship between BMI and delta-FIM appeared to be questionable in the scatter diagram if patients with BMI >40 kg/m were excluded. Third, the demographic data for the different BMI categories were insufficient. Previous reports have indicated many differences in the characteristics between BMI categories, such as age, sex and comorbidities. [2–6] This information may be useful for the interpretation of the results that there were no delta-FIM differences among the BMI categories. Fourth, this study did not include underweight subjects. Although the authors concluded that BMI negatively correlated with improvement in functional parameters,[1] careful interpretation might be required. Because being underweight is an independent predictive factor for death or functional dependency,[7] the findings of this study must be confined only to normal weight, overweight or obese participants. Finally, the number of participants in the multiple regression analysis was not described. Because relatively small number of participants were analyzed (n1⁄4 102) in this study, the effect of missing National Institute of Health Stroke Scale (NIHSS) scores on the statistical power cannot be ignored. The authors should have either excluded the participants without NIHSS scores or excluded the NIHSS score as a confounding factor in the multiple regression analysis. To date, there have been various controversial reports suggesting a beneficial effect of obesity in the functional recovery of patients with stroke. [1–6,8,9] The reasons for these inconsistencies may arise due to differences in race, methods of categorizing BMI, follow-up periods, functional indicators and other factors. We have previously reported that obese Japanese patients with stroke (BMI 27.5 kg/m) had greater FIM gain than those who were normal weight (18.5 to <23.0 kg/m) or overweight (23.0 to <27.5 kg/m). [2] Although our results were consistent with several other reports which investigated Asian populations,[3,6] the relationship between BMI and function disappeared after adjusting for stroke severity. [9] Additionally, a disturbed body composition, such as sarcopenic obesity, inhibits physical function. [10] Based on the aforementioned reasons, we believe that body composition and weight change (increasing muscle mass and decreasing fat mass) during the rehabilitation period are important factors in functional recovery of obese patients. We would like to discuss the inconsistent correlation between the obesity and functional outcome.