Distinction and mutual Influences between Parkinson's Disease-related and unrelated Chronic Pain

Background: Chronic pain (i.e. > 3 months) is a common nonmotor symptom in patients with Parkinson's disease (PD), but the attribution to PD is critical for further treatment. Objectives: We explored the PD Pain Classification System (PD-PCS) criteria for the diagnosis of PD-related pain and mutual influences between PD-related and PD-unrelated pain. Methods: In this multicenter study, 120 nondemented PD patients were assessed using the PD-PCS as well as motor and nonmotor questionnaires. The PD-PCS consists of 3 steps: first, it classifies chronic pain as unrelated or related to PD according to 1 of 4 criteria (at onset or aggravated by PD, in the off phase, improvement with dopaminergic treatment, and with dyskinesia); second, it allows the classification of pain mechanisms (neuropathic, nociceptive, and nociplastic); and finally, it provides a score. Results: Chronic pain was present in 92% of patients, with PD-related pain in 73% and non-PD-related pain in 53%. Higher PD-PCS scores were reported when PD-related pain was present. In cases of concurrent PD-related and PD-unrelated pain (35%), there was a moderate correlation between pain severity. Improvement with dopaminergic medication and pain in the off phases were the most common factors defining an association of pain with PD. These factors often occur together, whereas pain during dyskinesia occurs independently. Conclusion: The PD-PCS criteria allow differentiation between PD-related and PD-unrelated chronic pain through 2 approaches, assessing periods of either low or high dopaminergic stimulation. PD-unrelated pain should also be taken into account, as it is more common than in the general population and as it may influence PD-related pain.