The Parkinson's disease pain classification system (PDPCS): results from an international mechanism-based classification approach.

Pain is a common non-motor symptom in patients with Parkinson's disease (PD) but the correct diagnosis of the respective cause remains difficult because suitable tools are lacking, so far. We developed a framework to differentiate PD- from non-PD-related pain and classify PD-related pain into three groups based on validated mechanistic pain descriptors (nociceptive, neuropathic, or nociplastic), which encompass all the previously described PD pain types. Severity of PD-related pain syndromes was scored by ratings of intensity, frequency, and interference with daily living activities. The PD-Pain Classification System (PD-PCS) was compared with classic pain measures (ie, brief pain inventory (BPI) and McGill pain questionnaire (MPQ), PDQ-8 quality of life score, MDS-UPDRS scores, and non-motor symptoms). 159 non-demented PD patients (disease duration 10.2±7.6 years) and 37 healthy controls were recruited in four centers. PD-related pain was present in 122 patients (77%), with 24 (15%) suffering one or more syndromes at the same time. PD-related nociceptive, neuropathic, or nociplastic pain was diagnosed in 87 (55%), 25 (16%), or 35 (22%), respectively. Pain unrelated to PD was present in 35 (22%) patients. Overall, PD-PCS severity score significantly correlated with pain's BPI and MPQ ratings, presence of dyskinesia and motor fluctuations, PDQ-8 scores, depression and anxiety measures. Moderate intra- and inter-rater reliability was observed. The PD-PCS is a valid and reliable tool for differentiating PD-related pain from PD-unrelated pain. It detects and scores mechanistic pain subtypes in a pragmatic and treatment-oriented approach, unifying previous classifications of PD-pain.