Not described

Abbreviations: LB, Lewy body; NFT, neurofibrillary tangles.

Abbreviations: LB, Lewy body; NFT, neurofibrillary tangles.

Lewy Body Disease

As mentioned previously, the most common pathologic substrate of PD is LBD. LBs are granulofilamentous intraneuronal inclusions composed of a-synuclein and other proteins (5) (Figs. 1A and 2A). Typical LBs are easily recognized, round cyto-plasmic inclusions, but more subtle lesions are also found, the so-called cortical LBs (Figs. 1D and 2D). Neurons with LBs are susceptible to cell death and phagocytosis by microglia, a process referred to as neuronophagia (Fig. 1B). Inclusions similar to LBs are also found within neuronal processes as intraneuritic LBs (Figs. 1C and 2C). In addition to these lesions, which are readily detected with routine histologic methods, there are also more subtle neuritic lesions that contain abnormal aggregates of a-synuclein, known as Lewy neurites (LNs) (Fig. 2D). LNs are only visible with immunohistochemical methods, while intraneuritic LBs can be detected with routine histologic methods (Fig. 1C). While originally described in the hippocampus (6) and later the amygdala (7), LNs are now known to be more widely distributed than originally suspected and may be the most abundant type of pathologic lesion in any given region affected by the disease process. They may also be the earliest cytologic alteration in affected neurons (8), and they may precede LB formation in perikarya or axons (9). The contribution of neuritic degeneration to the clinical phenotype is increasingly recognized (10).

The vulnerability of selected populations of neurons to LBs has been known for many years [(11-13); reviewed in (14)] and is the focus of increasing interest. Neurons that are most vulnerable to LBs include the monoaminergic neurons of the substantia nigra, locus ceruleus, and raphe nuclei (Fig. 3), as well as the cholinergic neurons of the basal forebrain. Due to the neuronal loss of pigmented neurons in the substantia nigra and locus ceruleus, these nuclei show loss of neuromelanin pigmentation on gross examination (Fig. 3). This neuronal loss corresponds to decrease in dopaminergic terminals in the striatum as detected by tyrosine hydroxylase immunohistochemistry, the rate-limiting enzyme in dopamine synthesis (Fig. 4).


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