Short latency afferent inhibition: a biomarker for mild cognitive impairment in Parkinson's disease?

BACKGROUND: Mild cognitive impairment in Parkinson's disease (PD) is common and predicts those at risk of dementia. Cholinergic dysfunction may contribute to its pathophysiology and can be assessed using short latency afferent inhibition.
METHODS: Twenty-two patients with PD (11 cognitively normal; 11 with mild cognitive impairment) and 22 controls participated. Short latency afferent inhibition was measured by conditioning motor evoked potentials, which were elicited by transcranial magnetic stimulation of the motor cortex with electrical stimuli delivered to the contralateral median nerve at varying interstimulus intervals.
RESULTS: There was no significant difference between cognitively normal PD and controls for short latency afferent inhibition (62.8±30.3% vs. 55.7±21.7%; P=0.447). The PD-mild cognitive impairment group had significantly less inhibition (88.4±25.8%) than both cognitively normal PD (P=0.021) and controls (P=0.01).
CONCLUSIONS: Cholinergic dysfunction occurs early in those with PD-mild cognitive impairment. Short latency afferent inhibition may be a useful biomarker of increased risk of dementia in PD patients. © 2013 Movement Disorder Society.