F63. Short latency afferent inhibition predicts cholinergic deficit in Parkinson’s disease patients with mild cognitive impairment

Abstract

Introduction In vivo evaluation of cholinergic circuits of the human brain had been introduced by using short latency afferent inhibition (SAI). This protocol is coupled motor cortex transcranial stimulation (TMS) with prior contralateral peripheral nerve stimulation. SAI is reduced in deficient cholinergic brain condition and restored with drugs enhancing cholinergic transmission. Cholinergic deficits have been considered involved in Parkinson’s disease (PD) with cognitive decline. In the study, we investigated whether SAI can be a useful tool for evaluating PD with cognitive decline. Methods Twenty-three advanced PD patients admitted for deep brain stimulation pre-surgical evaluation in Hualien Tzu-Chi hospital were enrolled to the study. The SAI test was performed in OFF state. CASI and MMSE were measured for cognitive evaluation. Results Motor evoked potential (MEP) in eight PD patients with severe tremor were discarded because of poor quality. Ten patients with normal cognition (MMSE 27–30), the SAI-22 (inter-stimulation interval: 22 ms) was 34.73% and SAI-25 (inter-stimulation interval: 25 ms) was 38.9%. Five patients with mild cognitive impairment (MMSE 24–26), the SAI-22 was 54.47% and SAI-25 was 81.32%. Compared the two groups, SAI-25 was significantly different (with unpaired T-test), reduced SAI-25 was found in PD with mild cognitive impairment. Conclusion The short latency inhibition (SAI-25) effectively detect the cholinergic deficits in PD with mild cognitive impairment.