Impaired Pain Processing Correlates with Cognitive Impairment in Parkinson's Disease

Objective Pain and cognitive impairment are important clinical features in patients with Parkinson's disease (PD). Although pain processing is associated with the limbic system, which is also closely linked to the cognitive function, the association between pain and cognitive impairment in PD is still not well understood. The aim of the study was to investigate the association between pain processing and cognitive impairment in patients with PD. Methods Forty-three patients with PD and 22 healthy subjects were studied. Pain-related somatosensory evoked potentials (SEPs) were generated using a thin needle electrode to stimulate epidermal Aδ fibers. Cognitive impairment was evaluated using the Mini-Mental State Examination (MMSE), the Frontal Assessment Battery, and Japanese version of the Montreal Cognitive Assessment (MoCA-J), and their correlation with pain-related SEPs was investigated. Results The N1/P1 amplitude was significantly lower in PD patients than the controls. N1/P1 peak-to-peak amplitudes correlated with the MMSE (r=0.66, p<0.001) and MoCA-J scores (r=0.38, p<0.01) in patients with PD. These amplitudes also strongly correlated with the domains of attention and memory in the MMSE (attention, r=0.52, p<0.001; memory, r=0.40, p<0.01) and MoCA-J (attention, r=0.45, p<0.005; memory, r=0.48, p<0.001), but not in control subjects. Conclusion A good correlation was observed between the decreased amplitudes of pain-related SEPs and an impairment of attention and memory in patients with PD. Our results suggest that pathological abnormalities of the pain pathway are significantly linked to cognitive impairment in PD.