Distinct FP-CIT PET patterns of Alzheimer’s disease with parkinsonism and dementia with Lewy bodies

Little is known regarding the clinical relevance or neurobiology of subtle motor disturbance in Alzheimer’s disease (AD). This study aims to investigate the patterns of striatal 18F-FP-CIT uptake in patients with AD-related cognitive impairment (ADCI) with mild parkinsonism. We recruited 29 consecutive patients with ADCI with mild parkinsonism. All patients underwent 18F-FP-CIT PET scans and dopamine transporter (DAT) availability in striatal subregions (anterior/posterior caudate, anterior/posterior putamen, ventral putamen, ventral striatum) was quantified. Additionally, 32 patients with dementia with Lewy bodies (DLB) and 21 healthy controls were included to perform inter-group comparative analyses of the striatal DAT availability. The discriminatory power of striatal DAT availability to differentiate ADCI from DLB was assessed using receiver operating characteristics (ROC) analyses. The Spearman’s correlation coefficient was calculated to assess the relationship between motor severity and DAT availability in striatal subregions. Patients with ADCI with mild parkinsonism exhibited decreased DAT availability in the caudate that was intermediate between healthy controls and patients with DLB. The DAT availability in other striatal subregions, including the posterior putamen, did not differ between the ADCI with parkinsonism and healthy control groups. The ROC analysis showed that DAT availability of all striatal subregions, especially the whole striatum, had a fair discriminatory power. Parkinsonian motor severity did not correlate with the striatal DAT availability in ADCI with parkinsonism. The present study demonstrated that patients with ADCI with mild parkinsonism had distinct DAT scan patterns and suggests that parkinsonism is associated with the extranigral source of pathology.