[Neuropathic pain unrelieved by morphine, alleviated by haloperidol]

Neuropathic pain, originating in damaged nerve and not peripheral nociceptors, is often resistant to treatment by opiates given by the oral, parenteral or spinal routes. This failure to obtain satisfactory pain relief is generally ascribed to psychological factors or to individual peculiarities in drug metabolism or kinetics. Currently, psychotropic and antidepressant drugs are among the first choices in treating painful conditions due to partial nerve lesions. We present a 56-year-old man who suffered intractable pain confined to his left knee following emergency L2-3 vertebral decompression, after collapse due to metastatic disease. 12 mg of morphine and 10 of diazepam given together intravenously did not lessen pain. Acute, solitary spinal nerve root injury was hypothesized. 2 mg of haloperidol injected IV gave complete relief of pain without hypotension or deep sedation. There is no definite explanation for the resistance of neuropathic pain to opiates.