Limbic lobe microvacuolation is minimal in Alzheimer's disease in the absence of concurrent Lewy body disease.

Microvacuolation is relatively common in the limbic lobe in Lewy body disease (LBD). Similar pathology has also been reported in Alzheimer's disease (AD). Almost all of the studies of microvacuolation in AD, however, antedated the routine application of sensitive immunohistochemical methods to detect Lewy bodies. This raises the possibility that microvacuolation previously reported in AD may have been due to unrecognized LB pathology. To explore this issue, alpha-synuclein immunohistochemistry was used to evaluate a consecutive series of AD as well as cases with mixed AD and LBD (AD/LBD). Independently, the degree of microvacuolation was graded in the entorhinal cortex and the amygdala of the same cases. The results showed that microvacuolation was more common and more severe in AD/LBD than in pure AD cases. In pure AD cases microvacuolation was related to senile plaque density, especially in the amygdala, where many of the neuropil vacuoles were around dense-cored, neuritic plaques. In contrast, in AD/LBD microvacuolation correlated with LB density in the entorhinal cortex and amygdala. These results suggest that microvacuolation has a different pathogenesis in AD and in AD/LBD. Moreover, when prominent microvacuolation is detected in AD, it is imperative to exclude concurrent LBD.