Objective: Investigation of the neurophysiological disorders and identify their structural correlates in the brain by MRI studies with using voxel-based morphometry to reveal subtle changes in gray matter volume in PD patients with pain syndromes.

Background: Pain syndromes (PS) in Parkinson’s disease (PD) are complex pathology in the somatosensory and autonomic systems leading to disorders in the subcortical-brainstem-spinal systems functions in which specific brain structural changes may also occur.

Method: We used short-latency somatosensory evoked potentials (SEPs), blink reflex (BR) investigation which provides information about the afferent pathways and can assess the functional integrity of supraspinal structures and their descending influence on the brainstem. MRI scanning was conducted on a 3T scanner and data were processed using the FreeSurfer 6.0 software.
52 patients with PD were examined in the age range of 40-70 years: 22 with PS  (1st group) and 20 -without PS (2nd group). 25 age-match healthy individuals were included in the control group. The 1st group included PD patients with unexplained PS that corresponded to the side of motor manifestations, or pain in the perineum, face, mouth; PS changed with levodopa.

Results: In PD patients with PS it was revealed neurophysiological sign of sensitization processes at the level of brainstem and thalamocortical projections according to the SEP. A significant decrease in the second BR components latency and increase in their amplitude, indicate polysynaptic hyperexcitability. In PD patients, caudate and precentral gurus volumes from both sides were significantly diminished as compared to the control group, which may reflect the general neurodegenerative process associated with PD. 3rd and 4th ventricles were markedly dilated and volumes in the postcentral gyrus were significantly lower in PD patients with PS. There was  significant increase in the thalamus grey matter volume in 1st group as compared with 2nd group.

Conclusion: The tendency to hyperexcitable BR response is explained by insufficiency of inhibition mechanisms at the brainstem level and deficiency of supraspinal descending control in PD patients with PS. Identified by MRI voxel-based analysis the structural changes in certain brain structures probably associated with functional neurophysiologic abnormalities and can be considered as a predisposition  to the appearance of pain syndromes in PD patients.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/pain-syndrome-in-parkinsons-disease-neurophysiological-and-mri-morphometric-features/