Eight cancer patients in the terminal stages of the disease treated wi
th high doses of intravenous morphine developed hyperalgesia. All case
s were retrospectively sampled from three different hospitals in Copen
hagen. Five patients developed universal hyperalgesia and hyperesthesi
a which in 2 cases were accompanied by myoclonus. In 3 patients a pre-
existing neuralgia increased to excruciating intensity and in 2 of the
se cases myoclonus occurred simultaneously. Although only few clinical
descriptions of the relationship between hyperalgesia/myoclonus and h
igh 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 a
re discussed and treatment proposals given suggesting the use of more
efficacious opioids with less excitatory potency in these situations.