BACKGROUND: Dementia is a frequent complication of idiopathic parkinsonism or 
PD, usually occurring later in the protracted course of the illness. The primary 
site of neuropathologic change in PD is the substantia nigra, but the 
neuropathologic and molecular basis of dementia in PD is less clear. Although 
Alzheimer's pathology has been a frequent finding, recent advances in 
immunostaining of alpha-synuclein have suggested the possible importance of 
cortical Lewy bodies (CLBs) in the brains of demented patients with PD.
METHODS: The brains of 22 demented and 20 nondemented patients with a clinical 
and neuropathologic diagnosis of PD were evaluated with standard neuropathologic 
techniques. In addition, CLBs and dystrophic neurites were identified 
immunohistochemically with antibodies specific for alpha-synuclein and 
ubiquitin; plaques and tangles were identified by staining with thioflavine S. 
Associations between dementia status and pathologic markers were tested with 
logistic regression.
RESULTS: CLBs positive for alpha-synuclein are highly sensitive (91%) and 
specific (90%) neuropathologic markers of dementia in PD and slightly more 
sensitive than ubiquitin-positive CLBs. They are better indicators of dementia 
than neurofibrillary tangles, amyloid plaques, or dystrophic neurites.
CONCLUSION: CLBs detected by alpha-synuclein antibodies in patients with PD are 
a more sensitive and specific correlate of dementia than the presence of 
Alzheimer's pathology, which was present in a minority of the cases in this 
series.