The effects of a dopamine agonist (apomorphine) on experimental and spontaneous pain in patients with chronic radicular pain: A randomized, double-blind, placebo-controlled, cross-over study

BackgroundAlthough evidence suggests that dopaminergic systems are involved in pain processing, the effects of dopaminergic interventions on pain remains questionable. This randomized, double blinded, placebo-controlled, cross-over study was aimed at exploring the effect of the dopamine agonist apomorphine on experimental pain evoked by cold stimulation and on spontaneous pain in patients with lumbar radicular (neuropathic) pain.MethodsData was collected from 35 patients with chronic lumbar radiculopathy (18 men, mean age 56.2±13 years). The following parameters were evaluated before (baseline) and 30, 75 and 120 minutes subsequent to a subcutaneous injection of 1.5 mg apomorphine or placebo: cold pain threshold and tolerance in the painful site (ice pack, affected leg) and in a remote non-painful site (12°C water bath, hand), and spontaneous (affected leg) pain intensity (NPS, 0–100).ResultsOne-hundred and twenty minutes following apomorphine (but not placebo) injection, cold pain threshold and tolerance in the hand increased significantly compared to baseline (from a median of 8.0 seconds (IQR = 5.0) to 10 seconds (IQR = 9.0), p = 0.001 and from a median of 19.5 seconds (IQR = 30.2) to 27.0 seconds (IQR = 37.5), pConclusionThese findings are in line with previous results in healthy subjects, showing that apomorphine increases the ability to tolerate cold pain and therefore suggesting that dopaminergic interventions can have potential clinical relevance.背景 尽管已有证据表明多巴胺能系统（dopaminergic systems）参与疼痛加工过程，但多巴胺能干预措施对疼痛的影响仍有待商榷。本项随机双盲安慰剂对照交叉试验旨在探讨多巴胺受体激动剂阿扑吗啡（apomorphine）对冷刺激诱发的实验性疼痛，以及腰椎神经根性（神经性）疼痛患者自发性疼痛的影响。 方法 本研究纳入35例慢性腰椎神经根病患者（其中男性18例，平均年龄56.2±13岁）。在皮下注射1.5mg阿扑吗啡或安慰剂前（基线状态）及注射后30、75、120分钟，对以下参数进行评估：疼痛部位（患侧下肢，采用冰袋刺激）与远端非疼痛部位（手部，采用12℃水浴刺激）的冷痛阈值与冷痛耐受力，以及患侧下肢的自发性疼痛强度（数字疼痛评分量表（NPS）0~100分）。 结果 注射阿扑吗啡（而非安慰剂）后120分钟，手部的冷痛阈值与冷痛耐受力较基线显著升高：冷痛阈值从中位数8.0秒（四分位距（Interquartile Range, IQR）=5.0）升至10秒（IQR=9.0，p=0.001），冷痛耐受力从中位数19.5秒（IQR=30.2）升至27.0秒（IQR=37.5，p 结论 本研究结果与健康受试者的既往研究结果一致，表明阿扑吗啡可提升机体对冷痛的耐受能力，提示多巴胺能干预措施或具有潜在的临床应用价值。