Later-Developing Dementia and Loss of the Levodopa Response

We identified 13 patients with a clinical diag-nosis of PD who experienced dementia at least 4 yearsafter parkinsonism onset (mean, 10.5 years) and subse-quentlyunderwentpostmortemexamination.Despitele-vodopa therapy, 9 patients later became severely im-paired and nonambulatory, requiring total or near-totalcare; this included 4 patients treated with 1200 mg/d ormore of levodopa (with carbidopa), which was consis-tent with loss of the levodopa response. These 13 pa-tients were compared with 9 patients clinically diag-nosed as having PD, but without dementia, who hadundergone autopsies.