Central pain in patients with Parkinson disease evaluated by pain-related evoked potentials

Pain is a well-recognized nonmotor manifestation of Parkinson disease (PD). This might be related to not only peripheral factors but also abnormal processing of nociceptive input in the central nervous system (CNS). To investigate possible dysfunction of pain pathway or of the processing of pain input in the CNS, we recorded pain-related evoked potentials induced by intra-epidermal electrical stimulation in patients with PD. Pain-related evoked potentials were recorded in 13 patients with PD and 21 healthy controls. The evoked potentials were recorded from the Cz electrode by intra-epidermal electrical stimulation, which is known to selectively stimulate A delta fibers, at the second digit on each of the 4 limbs. The amplitudes between N1 and P1, which are thought to originate from the cingulate cortex and the insula, were significantly lower in patients with PD compared with controls. Patients with PD showed no significant correlation between the severity of clinical parameters, such as Unified Parkinson's Disease Rating Scale or Hoehn and Yahr score, and the amplitudes between N1 and P1. In addition, no differences were found in mean N1 or P1 latency between the two groups. These results may reflect the existence of abnormal central processing of pain inputs in PD, which appears to be independent of the clinical expression of motor dysfunction.