Papers of the Week

Chronic pain is a frequent and burdensome non-motor symptom of Parkinson Disease (PD). PD-related chronic pain can be classified as nociceptive, neuropathic or nociplastic, the former being the most frequent subtype. However, differences in neurphysiologic profiles between these pain subtypes, their potential prognostic and therapeutic implications have not been explored yet. A cross-sectional study on patients with PD-related chronic pain (i.e., started with or was aggravated by PD). Subjects were assessed for clinical and pain characteristics through questionnaires, and undewent quantitative sensory test and motor corticospinal excitability evaluations. Data were then compared between individuals with nociceptive and non-nociceptive (i.e., neuropathic or nociplastic) pains. Thirty-five patients were included (51.4% male, 55.7±11.0 years-old), 20 of which had nociceptive pain. Patients with nociceptive PD-related pain had lower warm detection (WDT, 33.34±1.39 vs. 34.34±1.72, p=0.019) and mechanical detection thresholds (MDT, 2.55±1.54 vs. 3.86±0.97, p=0.007) compared with those with non-nociceptive pains. They also presented a higher proportion of low RMT values than the non-nociceptive pain ones (64.7% vs. 26.6%, p=0.048). In non-nociceptive pain patients there was a negative correlation between WDT and non-motor symptoms scores (r=-0.612, p=0.045), and a positive correlation between MDT and average pain intensity (r=0.629, p=0.038), along with neuropathic pain symptom scores (r=0.604, p=0.049). It is possible to conclude that PD-related chronic pain subtypes have distinctive somatosensory and corticospinal excitability profiles. These preliminary data may help better frame previous contradictory findings in patients with PD and may have implications for future trial designs aiming at developing individually tailored therapies. PERSPECTIVE: This work showed that patients with Parkinson Disease-related nociceptive chronic pain may have distinctive somatosensory and corticospinal excitability profiles than those with non-nociceptive pain subtypes. These data may help shed light on previous contradictory findings in patients with Parkinson Disease, and guide future trials aiming at developing individually-tailored management strategies.