beta -amyloid precursor protein positive axonal bulbs may form in non-head-injured patients

Since the early 1980s axonal bulbs staining positively for beta-amyloid precursor protein (betaAPP) have been used as a marker of diffuse axonal injury (DAI), bulb formation been attributed to shearing forces generated during rotational acceleration/deceleration head injury. This study draws attention to the observation that they may form in the absence of a head injury and, thus, axonal injury cannot be assumed to result from mechanical injury alone. Out of 20 cases with no history of head injury studied, which only showed evidence of neuronal hypoxic change, 11 (55%) showed variable positive staining for betaAPP in a similar anatomical distribution to that previously described for DAI. The role of hypoxia in the formation of axonal bulbs, as well as the possible role of betaAPP as an acute phase protein, are discussed. These observations further clarify the pattern and relationship between neuronal and axonal staining observed following a brain insult and emphasize the possible role of betaAPP as a neuroprotective protein.