Myoclonic spasms following intrathecal diamorphine

The use of intrathecal diamorphine via an implanted portal system is described for pain control in a patient suffering from vertebral metastatic disease. The complication of myoclonic spasms affecting the lower half of the body occurred after 14 days, when increasing the bolus dose to 40 mg. The spasms lasted for 3 hr and then gradually subsided. Diamorphine was subsequently restarted at a lower dose of 15 mg twice daily. On increasing the dose to 20 mg diamorphine 10 days later, severe distressing myoclonic spasms recurred 20 min postinjection. Myoclonus could only be controlled by instituting a local anesthetic intrathecal block. The patient was finally managed with 20 mg diamorphine per day by intrathecal infusion, and the pain was reasonably well controlled for the following 10 weeks without any recurrence of myoclonic spasms.