How pain arises in Parkinson's disease?

In recent years, increasing attention has centred on pain in Parkinson's disease (PD). Pain in PD is heterogeneous in quality and body distribution. To clarify how the various pain types relate to PD and to propose plausible treatment strategies, in this paper we reviewed psychophysical, neurophysiological and imaging data reported in parkinsonian patients with and without pain. Most available evidence supports abnormal central nociceptive input processing that probably reflects an impairment in the lateral and medial pain pathways. Changes in central pain processing probably underlie all the different pain types and also intervene in patients with PD without pain. Thus, altered pain processing might predispose patients with PD to spontaneous pain that is variable in quality. These background pain-processing abnormalities may interact with additional factors (such as contractures secondary to marked rigidity/bradykinesia, dystonia and medical conditions associated with painful symptoms), thus causing pain to manifest itself clinically in various ways and providing candidate targets for pain treatment in PD.