Pain
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Case Reports
Hyperalgesia and myoclonus in terminal cancer patients treated with continuous intravenous morphine.
Eight cancer patients in the terminal stages of the disease treated with high doses of intravenous morphine developed hyperalgesia. All cases were retrospectively sampled from three different hospitals in Copenhagen. ⋯ Although only few clinical descriptions of the relationship between hyperalgesia/myoclonus and high doses of morphine are available, experimental support from animal studies indicates that morphine, or its metabolites, plays a causative role for the observed behavioural syndrome. The possible mechanisms are discussed and treatment proposals given suggesting the use of more efficacious opioids with less excitatory potency in these situations.
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The aim of this study was to determine the effects of sympathectomy on our previously developed animal model for neuropathic pain. The neuropathy was produced by a unilateral tight ligation of the L5 and L6 spinal nerves in 81 rats, all of which showed a marked increase in frequency of paw lifting in response to innocuous mechanical stimuli and a shortened latency of paw withdrawal in response to noxious radiant heat stimuli on the affected limb. We interpreted these as behavioral signs of mechanical allodynia and heat hyperalgesia. ⋯ The effect of sympathectomy for mechanical allodynia is estimated to be almost fully expressed within 30 min after the operation. Sympathetic block by chemical agents reversibly relieved the mechanical allodynia. These data suggest that the rats in our model exhibit behavioral signs of neuropathic pain that are sympathetically maintained.