The threshold of pain and neurotransmitter's change on pain in Parkinson's disease.

Among Parkinson's disease (PD) patients complaining of pain, 10 with pain not associated with a motor fluctuation or L-dopa therapy were evaluated. The controls were 14 PD without pain and eight with thalamic pain syndrome. The threshold of pain and neurotransmitters in CSF were measured in the three groups. In PD with pain, the maximum tolerance level and tourniquet pain ratio decreased significantly. In PD with pain, the score on the self-depression scale increased significantly and 5-hydroxy-indole acetic acid (5-HIAA) among the neurotransmitters decreased significantly. These results suggest that decreases in the threshold of pain and changes of serotonin in CSF are involved in the development of specific pain in PD who do not respond to L-dopa.