Interaction between increasing body mass index and spinal cord injury to the probability of developing a diagnosis of nonalcoholic fatty liver disease

BACKGROUND: The prevalence of obesity and comorbidities is high in the population with spinal cord injury (SCI). We sought to determine the effect of SCI on the functional form of the relationship between body mass index (BMI) and risk of developing nonalcoholic fatty liver disease (NAFLD), and assess whether SCI‐specific mapping of BMI to risk of developing NAFLD is needed. METHODS: Longitudinal cohort study comparing Veterans Health Administration patients with a diagnosis of SCI to a 1:2 matched control group without SCI. The relationship between BMI and development of NAFLD at any time was assessed with propensity score matched Cox regression models; NAFLD development at 10‐year with a propensity score matched logistic model. The positive predictive value of developing NAFLD at 10 years was calculated for BMI 19–45 kg/m(2). RESULTS: 14,890 individuals with SCI met study inclusion criteria, and 29,780 Non‐SCI individuals in matched control group. Overall, 9.2% in SCI group and 7.3% in Non‐SCI group developed NAFLD during the study period. A logistic model assessing the relationship between BMI and the probability of developing a diagnosis of NAFLD demonstrated that the probability of developing disease increased as BMI increased in both cohorts. The probability was significantly higher in the SCI cohort at each BMI threshold (p < 0.01), and increased at a higher rate compared with the Non‐SCI cohort as BMI increased 19–45 kg/m(2). Positive predictive value for developing a diagnosis of NAFLD was higher in the SCI group for any given BMI threshold from 19 kg/m(2) to BMI 45 kg/m(2). CONCLUSIONS: The probability of developing NAFLD is greater in individuals with SCI than without SCI, at every BMI level 19 kg/m(2) to 45 kg/m(2). Individuals with SCI may warrant a higher level of suspicion and closer screening for NAFLD. The association of SCI and BMI is not linear.