# Changes in conditioned pain modulation using anti-Parkinson drugs in patients with Parkinson's disease

## TL;DR

Anti-Parkinson drugs may improve the body's natural ability to suppress pain in Parkinson's disease patients.

## Contribution

This study shows that anti-Parkinson drugs enhance 'pain inhibits pain' mechanisms in Parkinson's patients.

## Key findings

- Anti-Parkinson drugs increased conditioned pain modulation during cold pressure tests.
- CSP duration shortened more under drug-on conditions compared to drug-off conditions.
- Pain ratings correlated with CSP changes, suggesting drug effects on pain control.

## Abstract

Patients with Parkinson's disease (PD) highly complain of pain, probably due to the lowered pain threshold caused by dopamine deficiency. Nonetheless, only a few studies have investigated the effects of anti-PD medications on “pain inhibits pain” ability. This study aimed to evaluate conditioned pain modulation (CPM) using the cutaneous silent period (CSP) and the numerical rating scale (NRS) and to investigate the effect of anti-PD medications on CPM.

The CSP was recorded in 40 patients with PD under drug-on and drug-off conditions. Changes in the CSP elicited by electrical test stimulation and in the NRS when the patients experienced pain with cold pressure as a conditioned stimulus were assessed. A shortened CSP duration or reduced CSP score due to cold pressure were interpreted as objective CPM responses.

The CSP latency was analyzed in 22 patients when the electromyographic contamination in the CSP waveform was low. The CSP duration shortening during cold pressure was significantly greater under the drug-on condition than under the drug-off condition. The change in CSP duration exhibited a significant correlation with the change in the NRS scores. CSP score analysis was performed on 18 patients in whom latency analysis was difficult owing to electromyographic contamination. In the drug-on state, conditioned cold-pressure pain significantly decreased the CSP score.

Dynamic changes in the CSP caused by cold pressure in patients with PD suggest that anti-PD medications may enhance CPM ability.

In the cartoon, the little “pain devil” runs away when a bigger “pain devil” shows up. This “pain inhibits pain” effect can be measured with EMG (cutaneous silent period) during a cold pressor test. It shows how the descending pain control system suppresses pain.We found that this effect got stronger after taking an anti‑Parkinsonian drug.Unlabelled Image

In the cartoon, the little “pain devil” runs away when a bigger “pain devil” shows up. This “pain inhibits pain” effect can be measured with EMG (cutaneous silent period) during a cold pressor test. It shows how the descending pain control system suppresses pain.We found that this effect got stronger after taking an anti‑Parkinsonian drug.

•Pain is common in Parkinson's disease, but descending pain inhibition remains underexplored.•“Pain inhibits pain” reflects a descending inhibitory mechanism testable in humans.•We used evoked electromyography and pain ratings to assess drug effects on pain control.•Anti-Parkinson drugs enhanced descending pain inhibition during cold pressure test.•Drug-related pain relief may differ depending on stage in Parkinson's disease.

Pain is common in Parkinson's disease, but descending pain inhibition remains underexplored.

“Pain inhibits pain” reflects a descending inhibitory mechanism testable in humans.

We used evoked electromyography and pain ratings to assess drug effects on pain control.

Anti-Parkinson drugs enhanced descending pain inhibition during cold pressure test.

Drug-related pain relief may differ depending on stage in Parkinson's disease.