Pain processing in atypical parkinsonisms and Parkinson disease. A comparative neurophysiological study

OBJECTIVE: Pain is a frequent non-motor feature in Parkinsonism but mechanistic data on the alteration of pain processing are insufficient to understand the possible causes and to define specifically-targeted treatments. METHODS: we investigated spinal nociception through the neurophysiological measure of the threshold (TR) of nociceptive withdrawal reflex (NWR) and its temporal summation threshold (TST) comparatively in 12 Progressive Supranuclear Palsy (PSP) subjects, 11 Multiple System Atrophy (MSA) patients, 15 Parkinson's disease (PD) subjects and 24 healthy controls (HC). We also investigated the modulatory effect of L-Dopa in these three parkinsonian groups. RESULTS: We found a significant reduction in the TR of NWR and in the TST of NWR in PSP, MSA and PD patients compared with HC. L-Dopa induced an increase in the TR of NWR in the PSP group while TST of NWR increased in both PSP and PD. CONCLUSIONS: Our neurophysiological findings identify a facilitation of nociceptive processing in PSP that is broadly similar to that observed in MSA and PD. Specific peculiarities have emerged for PSP. SIGNIFICANCE: Our data advance the knowledge of the neurophysiology of nociception in the advanced phases of parkinsonian syndromes and on the role of dopaminergic pathways in the control on pain processing.