Pain perception in Parkinson’s disease: A systematic review and meta-analysis of experimental studies

While hyperalgesia (increased pain sensitivity) has been suggested to contribute to the increased prevalence of clinical pain in Parkinson’s disease (PD), experimental research is equivocal and mechanisms are poorly understood. We conducted a meta-analysis of studies comparing PD patients to healthy controls (HCs) in their response to experimental pain stimuli. Articles were acquired through systematic searches of major databases from inception until 10/2016. Twenty-six studies met inclusion criteria, comprising 1292 participants (PD = 739, HCs = 553). Random effects meta-analysis of standardized mean differences (SMD) revealed lower pain threshold (indicating hyperalgesia) in PD patients during unmedicated OFF states (SMD = 0.51) which was attenuated during dopamine-medicated ON states (SMD = 0.23), but unaffected by age, PD duration or PD severity. Analysis of 6 studies employing suprathreshold stimulation paradigms indicated greater pain in PD patients, just failing to reach significance (SMD = 0.30, p= = 0.06). These findings (a) support the existence of hyperalgesia in PD, which could contribute to the onset/intensity of clinical pain, and (b) implicate dopamine deficiency as a potential underlying mechanism, which may present opportunities for the development of novel analgesic strategies

Pain threshold and polysynaptic components of the blink reflex in Parkinson's disease.

This study was conducted on 15 outpatients with idiopathic Parkinson's disease, 10 on chronic levodopa therapy and 5 drug free, all complaining of painful syndromes. We investigated the perceptive and pain thresholds and the threshold of polysynaptic components of the blink reflex in patients and 8 controls. Our data indicate that as regards the perceptive, pain and R2, R3 thresholds, patients with and without levodopa therapy do not differ significantly from controls