Specificity and sensitivity of beta APP in head injury

Introduction: beta -amyloid precursor protein (beta APP) expression has bee n found in traumatic brain injury, hypoxia, ischemia and infection which af fect axonal transport. Although beta APP is a sensitive marker for detectin g axonal damage, it has become non-specific for a particular type of injury . The aim of this study was to identify a difference in the pattern, distri bution and intensity of beta APP expression in head injury compared to hypo xic/ischemic insults. Materials and methods: Thirteen primary head injury a nd 12 primary hypoxic/ischemic cases were selected. The anterior and poster ior parts of corpus callosum, internal capsule (basal ganglia), middle cere bellar peduncles (cerebellum) and pons were examined and stained immunohist ochemically for beta APP antibody. A computerized system of image analysis was used to examine the intensity (strength of staining) and density (area fraction) of beta APP. Results: Significant differences were observed in th e overall intensity and density of beta APP expression (p < 0.05) and in al l 5 brain regions in cases of head injury compared to the hypoxic/ischemic group (p < 0.05). Positive staining for beta APP was found in all regions i n all cases of head injury, however, 4 out of 12 cases of hypoxia/ischemia were positive for beta APP. One case expressed positivity in all 5 regions, 2 cases exhibited positivity in the pons alone, with only 1 case exhibitin g immunoreactivity in the posterior corpus callosum and internal capsule. D ifferences in the pattern of beta APP expression identified a predominantly granular pattern with a dirty background seen in hypoxia/ischemia, while f usiform swellings, beaded and thick filaments with clear background were ob served in head injury. Conclusion: There are differences in the pattern, di stribution and intensity of beta APP in head injury compared to hypoxia/isc hemia. These could be due to pathophysiological differences. The results ma y be helpful in differentiating head injury from hypoxia in medicolegal cas es.