Objective: This study aims to determine the relationship between pain threshold and striatal dopamine function in people with Parkinson’s disease.

Background: About 40-85% of Parkinson’s disease (PD) patients have been reported experiencing pain. In PD, degeneration of the brainstem nuclei disrupts dopaminergic, noradrenergic and serotonergic neurons. These neuropathological lesions may affect the descending pain suppression system to lower the pain threshold of PD patients. Furthermore, dysfunction in the mesolimbic dopamine pathway could lead to increased sensitivity to pain in the anterior cingulate cortex, the central area for pain perception. It has also been suggested that levodopa treatment can increase pain thresholds in patients with PD.

Method: Twelve patients with PD (mean age 71.3 ± 10.5 years, mean ± SD) and 12 healthy controls (64.6 ± 10.3 years) were evaluated by electrical pain threshold measurements in both forearms. The correlation between dopamine transporter SPECT specific binding ratio (SBR) and pain thresholds was investigated in PD patients.

Results: In the PD group, the pain thresholds were 10.54 μA in the right forearm and 15.14 μA in the left forearm for men and 7.61 μA in the right forearm and 8.60 μA in the left forearm for women, respectively. Females had significantly lower thresholds than males in the left forearm (p=0.007). In the control group, the thresholds in the right and left forearms were 10.57 μA each for men and 9.20 μA in the right forearm and 9.14 μA in the left forearm for women, with no significant age correlation or gender differences.

No significant difference in thresholds was observed between PD and control groups. In PD groups, a positive correlation was found between lower SBR and their contralateral forearm pain threshold (p=0.030).

Conclusion: There is no gender and age difference in the control group, but women with PD have significantly lower thresholds than men, and pain thresholds in PD may be strongly influenced by gender. Given the positive correlation between SBR and pain thresholds, it is possible that as SBR decreases beyond a certain level, pain thresholds also decrease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-relationship-between-pain-threshold-and-striatal-dopamine-function-in-parkinsons-disease/