Peripheral neuropathic pain in idiopathic Parkinson's disease: Prevalence and impact on quality of life; a case controlled study

Background and purpose: Pain is a frequent and debilitating non-motor symptom of Idiopathic Parkinson's Disease (IPD). The present study investigated the prevalence of pain and specifically peripheral neuropathic pain (PNP) in IPD, and ascertained any impact of PNP on quality of life (QoL). Methods: Patients with IPD and age- and gender-matched controls were screened for overall pain using the King's Parkinson's Pain Scale (KPPS). PNP was assessed using the Michigan Neuropathy Screening Instrument (MNSI). QoL was assessed using the 36-Item Short Form Survey (SF-36). Results: Fifty-one patients and 51 age and gender matched controls were recruited. The prevalence of overall pain was similar in the two groups (88.2% versus 94.1%, p = 0.487). However, patients with IPD had higher KPPS scores in fluctuation-related (4.9 +/- 6.9 vs 1.1 +/- 2.6, p < 0.001), nocturnal (6.6 +/- 7.5 vs 1.7 +/- 4.2, p < 0.001) and oro-facial (0.6 +/- 2.0 vs 0.0 +/- 0.0, p = 0.040) domains compared to controls. Patients with IPD experienced more PNP compared to healthy control subjects (35.3% versus 13.7%, p = 0.011). After adjusting for age, gender, disease duration and overall KPSS score, PNP correlated negatively with physical functioning score (beta - 0.290, p = 0.036), emotional role limitations score (beta - 0.319, p = 0.032) and general health perception score (beta - 0.342, p = 0.014) domains of SF-36. Conclusion: Peripheral neuropathic pain is prevalent in IPD and has a significant impact on QoL. The presence of burning pain is suggestive of small fibre neuropathy, but this symptom is not featured in KPSS and, therefore, a revision of the KPSS should be considered.