A characteristic parkinsonism with dementia [Parkinson dementia complex (PDC)] with a number of features that overlap with PSP (50) has been reported in the native Chamorro population of Guam since the 1950s (51). The frequency of PDC is declining in recent years for unknown reasons, and the etiology is unknown. The gross findings in PDC are notable for cortical atrophy affecting frontal and temporal lobes, as well as atrophy of the hippocampus and the tegmentum of the rostral brainstem (52). These areas typically have neuronal loss and gliosis with many NFTs in residual neurons.
Extracellular NFTs are also numerous. In the cortex, NFTs show a different laminar distribution from AD, with more NFTs in superficial cortical layers in Guam PDC and in lower cortical layers in AD (53). The hippocampus has numerous NFTs. The substan-tia nigra and locus ceruleus also have marked neuronal loss and many NFTs. The basal nucleus and large neurons in the striatum are also vulnerable to NFTs. Biochemically and morphologically, NFTs in Guam PDC are indistinguishable from those in AD (54).
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