Age and Anterior Basal Forebrain Volume Predict the Cholinergic Deficit in Patients with Mild Cognitive Impairment due to Alzheimer's Disease

Background: Early and severe neuronal loss in the cholinergic basal forebrain is observed in Alzheimer's disease (AD). To date, cholinomimetics play a central role in the symptomatic treatment of AD dementia. Although basic research indicates that a cholinergic deficit is present in AD before dementia, the efficacy of cholinomimetics in mild cognitive impairment (MCI) remains controversial. Predictors of cholinergic impairment could guide individualized therapy.

Objective: To investigate if the extent of the cholinergic deficit, measured using positron emission tomography (PET) and the tracer 11C-N-methyl-4-piperidyl acetate (MP4A), could be predicted from the volume of cholinergic basal forebrain nuclei in non-demented AD patients.

Methods: Seventeen patients with a high likelihood of MCI due to AD and 18 age-matched cognitively healthy adults underwent MRI-scanning. Basal forebrain volume was assessed using voxel-based morphometry and a cytoarchitectonic atlas of cholinergic nuclei. Cortical acetylcholinesterase (AChE) activity was measured using MP4A-PET.

Results: Cortical AChE activity and nucleus basalis of Meynert (Ch4 area) volume were significantly decreased in MCI. The extent of the cholinergic deficit varied considerably across patients. Greater volumes of anterior basal forebrain nuclei (Ch1/2 area) and younger age (Spearman's rho (17) = -0.596, 95% -CI [-0.905, -0.119] and 0.593, 95% -CI [0.092, 0.863])) were associated with a greater cholinergic deficit.

Conclusion: Data suggest that less atrophy of the Ch1/2 area and younger age are associated with a more significant cholinergic deficit in MCI due to AD. Further investigations are warranted to determine if the individual response to cholinomimetics can be inferred from these measures.