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Methods:12 patients with mild to moderate Alzheimer's disease and six controls were studied. The patients underwent ADAS-COG psychometric assessment and SPECT brain imaging with 123I quinuclidinyl benzilate (QNB), to demonstrate the postsynaptic muscarinic M1 receptor, before being randomised in a double blind study to receive either an acetylcholinesterase inhibitor (donepezil) or placebo for four months. Following this, the ADAS-COG and the 123I-QNB receptor scan were repeated. The controls were imaged on one occasion only. All image analyses were undertaken using SPM99.
Results:123I-QNB imaging showed a significant relation between baseline psychometric impairment and deficits on scanning. Both placebo and actively treated groups had reductions in 123I-QNB uptake. Greater reductions in receptor binding were demonstrated in the placebo group than in those receiving active treatment. Intraindividual reproducibility of the 123I-QNB imaging technique appeared highly robust.
Conclusions:The results suggest that 123I-QNB uptake is better preserved in Alzheimer's disease patients on cholinergic treatment than on placebo. Cholinergic treatment may play a neuroprotective role. Sequential 123I-QNB imaging seems to be a powerful tool in monitoring the response of these receptors to disease modifying treatments.