Effect of medical cannabis on thermal quantitative measurements of pain in patients with Parkinson's disease.

Background: Cannabis can alleviate pain of various etiologies. This study assessed the effect of cannabis on motor symptoms and pain parameters in patients with Parkinson's disease (PD). Methods: Twenty patients with PD who were licensed to use cannabis underwent evaluation before and 30 min after cannabis consumption and again after long-term use. Motor function was assessed with the Unified PD Rating scale (UPDRS) by two raters, one blinded. Pain was assessed with the Pain Rating Index (PRI) and Visual Analogue Scale (VAS) of the short-form McGill Pain Questionnaire. Thermal quantitative sensory testing (QST) was performed in 18 patients. The two consecutive QST measurements were validated in 12 cannabis-naive patients with Pd. Results: There was a significant decrease from baseline to 30 min after cannabis consumption in mean motor UPDRS score (38.1 +/- 18 to 30.4 +/- 15.6, p < 0.0001), total PRI (27 +/- 13.5 to 9.7 +/- 11, p = 0.001), and VAS score (6.4 +/- 2.8 to 3.6 +/- 3.1, p = 0.0005). Mean cold pain threshold decreased significantly in the more affected limb, but only after exclusion of two patients who consumed cannabis by vaporizer rather than smoking (19.5 +/- 5.2 to 15.6 +/- 8.7 degrees C, p = 0.02). After long-term (median 14 weeks) exposure, mean heat pain threshold decreased significantly in the more affected limb in all treated patients (43.6 +/- 3.5 to 40.9 +/- 3.3 degrees C, p = 0.05) and in cannabis smokers (43.7 +/- 3.6 to 40.3 +/- 2.5 degrees C, p = 0.008). Conclusions: Cannabis improved motor scores and pain symptoms in PD patients, together with a dissociate effect on heat and cold pain thresholds. Peripheral and central pathways are probably modulated by cannabis. Significance: Quantitative sensory test results are significantly altered following cannabis consumption in patients with PD. Cannabis probably acts on pain in PD via peripheral and central pathways.