Complications of spinal opioid therapy: myoclonus, spastic muscle tone and spinal jerking.

This study was made in order to define risk factors for patients requiring spinal opioid therapy developing painful spastic muscle tone together with myoclonus and spinal jerking (MSJ). The case histories of 75 patients, all receiving morphine spinally, were retrospectively analysed and, of these, 10 suffered from the MSJ syndrome. The following were taken as evaluation criteria: age, sex, performance status, duration and dosage of previous systemic and current spinal morphine therapy, concomitant analgesic and co-analgesic medication, pretreatment of the dorsal column and neurological dysfunction due to damage either of the nerval plexus or of the medulla spinalis. As a result, high spinal morphine doses in conjunction with pathological changes within the spine were shown to be risk factors for this syndrome. Changing from spinal to systemic morphine application or reduction of spinal doses together with the addition of systemic morphine led to complete recovery from MSJ. As underlying mechanism, an imbalance between the activity of spinal and central opioid receptors and/or toxic morphine effects on the medulla spinalis are discussed. In conclusion, great care should be taken when applying morphine to the spine in patients with neurological dysfunction due to an apparent pathology of the medulla spinalis, especially if large amounts of morphine are likely to be required. Some systemic application of morphine might reduce the risk of patients developing MSJ syndrome.