Levodopa raises objective pain threshold in Parkinson's disease: a RIII reflex study.
BACKGROUND
Patients suffering from Parkinson's disease (PD) describe painful sensations that could be related to neuropathic pain. Experimental data have indicated the involvement of basal ganglia and dopaminergic pathways in central nociceptive processing.


OBJECTIVE
The objective of this study was to assess and compare the effect of levodopa on the objective pain threshold in patients with PD and healthy subjects.


METHODS
The objective pain threshold was assessed by the nociceptive flexion reflex (RIII) in 13 PD patients and 10 healthy subjects. Patients and healthy subjects were evaluated under two randomised conditions: with levodopa (ON) and without (OFF).


RESULTS
Levodopa significantly increased the RIII threshold of PD patients (6.9 (1.2) mA in the OFF condition vs 8 (1.1) mA in the ON position; p = 0.02). RIII threshold was significantly lower in PD patients than in healthy subjects in the OFF condition (6.9 (1.2) mA vs 9.7 (3.4) mA; p = 0.02). RIII threshold did not change after levodopa administration in healthy subjects.


CONCLUSIONS
These results provide evidence of a dopaminergic modulation of objective pain threshold in PD patients. In addition, the decrease in RIII threshold in PD patients, in the OFF condition, compared with controls, confirms the existence of an objective pain perception disturbance in PD.
Gerdelat-Mas
A
A
Fédération de Neuroscience, Hôpital Purpan, Toulouse, France. gerdelat-mas.a@chu-toulouse.fr
Simonetta-Moreau
M
M
Thalamas
C
C
Ory-Magne
F
F
Slaoui
T
T
Rascol
O
O
Brefel-Courbon
C
C
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy* / Q000209:etiology* / Q000503:physiopathology; D017288:Pain Threshold / Q000187:drug effects*; D010300:Parkinson Disease / Q000150:complications*
D007980:Levodopa