Objective: To investigate pain-motor integration experimentally in patients with Parkinson’s disease (PD), with and without chronic pain.

Background: Although chronic pain is a common non-motor symptom in PD, the possible influence of chronic pain on Parkinsonian motor features in PD has been never investigated experimentally so far. We have recently designed a new transcranial magnetic stimulation (TMS) technique in healthy subjects (HS) to induce long-term (LTP)-like plasticity in the primary motor cortex (M1), as reflected by long-term changes in the amplitude of motor evoked potentials (MEPs), through pain-motor integration processes. This protocol combines the nociceptive system activation achieved by laser evoked potentials (LEPs), and M1 activation through TMS, in a laser-paired associative stimulation design (Laser-PAS).

Methods: In this study, to verify whether in PD, chronic pain influences cortical motor area function, we have applied our previously reported Laser-PAS protocol in Parkinsonian patients, with and without chronic pain. As experimental model to clarify whether in PD, the possible influence of chronic pain on cortical motor area function crucially reflects the presence of pain in the same body region manifesting motor symptoms, we compared responses to Laser-PAS in patients with chronic pain in the same body region investigated with Laser-PAS, with patients referring pain in other body regions not directly examined by Laser-PAS. Finally, to clarify the possible effect of dopaminergic replacement therapy (DRT), we applied Laser-PAS in patients with PD, with and without chronic pain, off and on therapy.

Results: We found reduced responses to Laser-PAS in PD patients, with and without chronic pain. When we compared responses to Laser-PAS in patients with and without chronic pain, we found similar abnormalities in the two patients’ subgroups. When we compared however, patients referring chronic pain in the right upper limb (the body region investigated with Laser-PAS) with those referring pain in other body regions, we found prominent changes in the former compared to the latter. Finally, when we compared patients off and on dopaminergic therapy, we found similar responses in these patients, regardless of the presence of chronic pain.

Conclusions: We conclude that in PD, chronic pain further degrades the response to Laser-PAS through mechanisms of abnormal pain-motor integration.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pain-motor-integration-in-the-primary-motor-cortex-in-parkinsons-disease/