Effects of Preexisting Diabetes Mellitus on the Severity of Traumatic Brain Injury.

Falls and traffic accidents can cause traumatic brain injury (TBI). Assessment of the injury severity is essential to determine the prognosis or the cause of death. Diabetes mellitus (DM) is a common preexisting disease in elderly adults. We hypothesized that preexisting DM exacerbates TBI secondary to prolonged inflammation. In this study, we investigated TBI-induced changes in nerve function and inflammatory cell migration to the injury site, and the extent of brain contusion in KK-Ay (DM) and C57BL/6J (non-DM) mice. A controlled cortical impact device was used to induce TBI in each mouse. The brain contusion volume was measured using magnetic resonance imaging. Nerve function changes were assessed using the following animal behavior tasks: neurological severity score (NSS), Morris water maze, forced swim test, and beam walking. Immunohistochemical examinations of brain sections were performed to assess the infiltration of neutrophils, astrocytes, microglia, and macrophages, and to detect apoptosis. These experiments were performed on post-injury days 1-90 (over five experiments/time-points in each group). Compared with non-DM mice, DM mice showed significantly greater brain contusion volume, greater deterioration in the NSS, and a higher number of neutrophils, macrophages, and apoptotic cells in the brain tissue specimens. This study indicates that the prognosis of normal mice and DM mice differs, even if they acquire a TBI of the same severity. Therefore, it is important to evaluate patients with TBI for DM and other preexisting diseases in order to provide adequate treatment or to determine the correct cause of death.