Impact of Complicated Diabetes Mellitus in Patients Following Severe Traumatic Brain Injury

Background The impact of diabetes mellitus (DM) on severe traumatic brain injury (TBI) outcomes remains poorly defined, with prior studies treating DM as a monolithic diagnosis. We hypothesized that post-TBI mortality is severity dependent, driven by pre-existing diabetic complications rather than the diagnosis of DM alone. Methods Retrospective cohort study utilized TriNetX. Patients with severe TBI were stratified into three cohorts: non-diabetic, uncomplicated DM, and complicated DM. Primary outcomes included: in-hospital mortality, 30-day readmission, and secondary systemic complications. Results 5,893 patients with complicated DM and 3,914 with uncomplicated DM were compared to matched non-diabetic controls. Patients with complicated DM had significantly higher mortality (33.8% vs. 29.7%; OR 1.21; 95% CI 1.12–1.30; P < 0.001), worse survival (HR 1.22; 95% CI 1.15–1.30; P < 0.001), and increased risks of 30-day readmission (OR 1.45), acute kidney injury (OR 1.29), sepsis (OR 1.23), pneumonia (OR 1.13), seizures (OR 1.18), cerebral infarction (OR 1.30), prolonged intubation/tracheostomy (OR 1.40), neurocritical care interventions (OR 1.50), CAUTI (OR 1.92), and CLABSI (OR 1.91) (all P < 0.05). In contrast, patients with uncomplicated DM demonstrated outcomes comparable to non-diabetic controls, with no increased mortality (27.9% vs. 28.4%; OR 0.98; P = 0.651), similar survival (HR 0.93; 95% CI 0.85–1.02; P = 0.168), and comparable rates of most complications, though they had lower 30-day readmission (OR 0.85; P = 0.002). Conclusion Severe TBI outcomes are critically dependent on preinjury diabetic complications, with the increased morbidity and mortality confined to preexisting complications. These findings reframe DM as a spectrum where microvascular integrity determines physiological resilience following neurological trauma.