The effect of residual neurological deficit on oral glucose tolerance in persons with chronic spinal cord injury

Study design: Oral glucose tolerance testing was performed prospectively in 201 subjects with spinal cord injury (SCI). The dependent variables included the values from the oral glucose tolerance test (glucose and insulin) and diagnostic classification (i.e., diabetes mellitus, impaired glucose tolerance, normal glucose tolerance); the independent variables consisted of study group, gender, ethnic group, age, age at onset of SCI, duration of injury, and anthropometric measurements. Objective: To determine the potential effects of level and completeness of SCI on oral glucose tolerance testing. In addition, the effects of gender ethnicity, age, age at onset of SCI, duration of injury, and anthropometric measurements on glucose tolerance were investigated. Setting: Subjects with chronic SCI were recruited during their annual physical examination at the Comarr Spinal Injury Clinic at Rancho Los Amigos Medical Center, Downey, California. Methods: An oral 75 g glucose load was administered after an overnight fast. Serum glucose was determined by autoanalyzer and plasma insulin levels, by radioimmunoassay. The results are reported as mean plus or minus standard error of the mean (mean +/- SEM). Analysis of variance (ANOVA) applying a Scheffe' post hoc F ratio was used for the continuous variables. Chi-squared analyses were performed to determine differences between the groups and among the subgroups for per cent distribution. Linear regression analyses were performed between variables of interest. Stepwise regression analyses were used to predict peak serum glucose concentration and peak plasma insulin level from potential determinants. Results: The total group consisted of 169 men with a mean age of 38 +/- 0.80 (range = 20 - 73) years and 32 women with a mean age of 44 +/- 2.13 (range = 20 - 72) years. The distribution by ethnicity for the total group with SCI consisted of 114(57%) Latino, 54 (27%) white, and 28) 14%) African American individuals. There was no significant difference in ethnic distribution among the subgroups for neurological deficit. Subjects were grouped by tetraplegia (Tetra; n=81) or paraplegia (Para; n=120) and by subgroup for degree of neurological deficit: complete Tetra (n=56), incomplete Tetra (n=25), complete Para (n=84), and incomplete Para (n=36). Of the total group, 27 subjects (13.4%) had diabetes mellitus and 56 (28.8%) had impaired glucose tolerance. Significantly more subjects in the complete Tetra group were classified with a disorder of carbohydrate metabolism than in the other neurological deficit subgroups (73 vs 44%, 24% and 31%, respectively for level of decreasing neurological deficit; X-2=36.9, P<0.0001). The complete Tetra group had significantly higher serum glucose concentrations at 60 min, 90 min, and 120 min and serum insulin concentration at 90 and 120 min compared with the other neurological subgroups (P<0.05 for each time point). No differences for plasma glucose were evident between men and women, however, plasma insulin levels were significantly higher for men at the intermediate time points (30 min, 60 min and 90 min), suggesting a relative state of insulin resistance in men. By stepwise regression analyses, higher peak serum glucose concentrations were associated with increased total body %fat, highest level of lesion (complete Tetra vs other neurological subgroups), older age at time of injury, and male gender; higher peak plasma insulin was associated with increased total body %fat and male gender. Conclusions: This study is the first to report that those individuals with the greatest levels of neurological deficit have increased risk of developing disorders of carbohydrate metabolism. Males with SCI are more insulin resistant than females. Glucose tolerance appears to be independent of the effects of ethnicity. Sponsorship: Funded in part by the National Institute on Disability and Rehabilitation Research (NIDRR) Grant # H133B30029. This work, would not have been possible without the gracious support of Quest Diagnostics, Inc.