Forensic tissue mechanics of diabetes mellitus-related brain induration

Brain induration is a classical autopsy finding historically linked to diabetes mellitus, though its underlying causes and specificity remain debated. Manual palpation to assess tissue stiffness is subjective. This study investigated whether biomechanical testing provides objective diagnostic value to assess tissue stiffness beyond time since death estimation. Brains from 44 adult autopsy cases were examined. Cylindrical samples from six different brain regions underwent oscillatory shear rheometry to determine storage, loss, and complex shear modulus. Cerebrospinal fluid and vitreous humor were analysed for glucose and lactate to calculate Traub sum values, and HbA1c was measured in venous blood when available. Autopsy reports were screened for medical history of diabetes mellitus and reported brain induration. Seven cases of the cohort had a known history of diabetes mellitus. Only one case of a known hyperosmolar hyperglycaemia prior to autopsy (Traub sum 636 mg/dl) was described as showing brain induration during autopsy. A second hyperosmolar hyperglycaemia case (Traub sum 458 mg/dl) also showed extreme stiffness but no reported induration. Both exhibited the lowest brain weights of the investigated cohort (1080 and 1120 g) and ranked among the top three stiffness values across all regions. Rheological stiffness significantly correlated with Traub sum values, but not with brain weight. Other causes of increased stiffness, such as traumatic brain injury with edema, produced high but regionally inconsistent values. Brain induration is associated with hyperosmolar hyperglycaemia rather than diabetes mellitus in general. Rheometry provided a sensitive, objective means to detect brain stiffening, whereas exceptionally stiff brains were not necessarily noted in autopsy reports based on routine manual palpation. KEY POINTS: • Brain stiffness seems to be associated with acute hyperosmolar hyperglycaemia rather than diabetes mellitus per se. • Diabetic cases without biochemical evidence of hyperosmolar hyperglycaemia showed no significant increase in brain stiffness. • Oscillatory shear rheometry provides an objective, quantitative measure of brain stiffness that outperforms manual palpation. • Rheologically measured brain stiffness correlated significantly with Traub sum values across all six examined brain regions. • Hyperosmolar hyperglycaemic cases showed consistently elevated stiffness across all brain regions.