Intrathecal morphine pump
Initial posting from: Bernard Bendok, MD
|This article has been reviewed by the NeuroWiki Editorial Board|
Intrathecal morphine pumps are used to treat patients with cancer and non-cancer related pain who no longer respond to oral narcotics, or who experience intolerable side-effects with systemic therapy. Intrathecal analgesia is effective in 60-75% of patients, including those with severe chronic pain. Proper patient selection requires a trial of intrathecal medication in conjunction with regular oral dosage. Adequate pain relief over several days suggests the device is fit for implantation.
A Tuohy needle is used to insert the catheter into the subarachnoid space at the lower lumbar level, which is then advanced to L1 or L2. Fluoroscopy ensures proper placement. Morphine distributes throughout the CSF and binds to receptors in the superficial layers of the spinal cord dorsal horn, producing analgesia regardless of the catheter’s dermatomal level.
Failed back surgery syndrome, rather than cancer, is the most common indication for intrathecal morphine. Cancer and non-cancer patients experience similar relief, though in the latter group tolerance may become problematic over time. Life expectancy must exceed 3 to 6 months in cancer patients to recoup the cost of implantation. Although neuropathic pain typically responds poorly to narcotics, numerous patients with supposedly neuropathic pain have experienced relief with intrathecal morphine. Therefore, the decision to treat needs to be empirical. In any patient, a successful trial is necessary before hardware internalization. During this time efficacy and rapid tolerization can be screened.
Initial implantation may be complicated by CSF leak and infection, although incidence is low. The catheter constitutes the weakest point in the system and may become occluded by scar tissue, kinked, dislodged, or serve as a nidus for granulation tissue. The latter situation is rare yet serious, presenting with increased pain and spinal cord or cauda equina compression. Patients receiving intrathecal morphine are not naïve to opiates, therefore side effects like respiratory depression, hypotension, and urinary retention are less likely. Others including edema, myoclonus, and reduced libido may also occur.
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- Brazenor GA. Long term intrathecal administration of morphine: a comparison of bolus injection via reservoir with continuous infusion by implanted pump. Neurosurgery. 1987 Oct;21(4):484-91.