Emerging analgesic drugs for Parkinson's disease

Introduction: Pain affects between 40 and 85% of Parkinson's disease (PD) patients. It is a frequently disabling and overlooked feature, which can significantly reduce health-related quality of life. Unfortunately, there are no universally recommended treatments for this condition. Areas covered: Evidence about the efficacy and safety of available analgesic treatments is summarized in this review. Potential targets for upcoming therapies are then discussed in light of what is currently known about the physiopathology of pain in PD. Protocols for efficacy and safety assessment of novel analgesic therapies are discussed. Finally, critical aspects of study protocol design such as patient selection or outcomes to be evaluated are discussed. Expert opinion: Preliminary results indicate that duloxetine, cranial electrotherapy stimulation, rotigotine, subthalamic or pallidum nuclei stimulation or lesion or levodopa could be effective for treating pain in PD. Similarly, some case reports indicate that repetitive transcranial magnetic stimulation (rTMS) or apomorphine could be effective for relieving painful off-period dystonia. Clinical trials with rTMS or oxycodone/naloxone prolonged-release tablets for neuropathic pain or botulinum toxin for off-period dystonia are underway. Success of clinical trials about analgesic strategies in PD will depend on the selection of the right PD population to be treated, according to the type of pain, and the proper selection of study outcomes and follow-up of international recommendations.