Severe peripheral edema during an outpatient continuous epidural morphine infusion trial in a patient with failed back surgery syndrome.

BACKGROUND Intraspinal drug delivery therapy has been increasingly used in patients with intractable, nonmalignant pain who fail to respond to conventional treatment or cannot tolerate systemic opioid therapy due to side effects. By infusing small amount of analgesics directly into the cerebrospinal fluid in close proximity to the receptor sites in the spinal cord, one is able to achieve the spinally mediated analgesia, sparing side effects due to systemic opioids. Prior to permanent intraspinal pump implantation, an intraspinal opioid screening trial is required to document the efficacy of intraspinal opioid for analgesia. Although there are a few approaches in conducting such screening trials, a patient controlled continuous epidural morphine infusion trial, performed in an outpatient setting, is widely accepted by many interventional pain specialists. The major advantage of conducting an outpatient trial is that it mimics what patients do in their daily living, therefore minimizing the false positive rate. OBJECTIVE To report a case of severe peripheral edema observed during an outpatient continuous epidural morphine infusion trial. CASE REPORT A 64-year-old female, with a 7-year history of severe low back pain and bilateral leg pain due to failed back surgery syndrome, was referred to our clinic for intraspinal drug delivery therapy after failing to respond to conservative treatment, including a previous history of 3 lumbosacral surgeries. Following a pre-implantation psychological evaluation confirming her candidacy, she underwent an outpatient patient-controlled continuous epidural morphine trial. A tunneled lumbar epidural catheter was placed at L2-L3 with catheter tip advanced to T12 under fluoroscopic guidance. Satisfactory catheter placement was confirmed by epidurogram. The proximal tip of the catheter was then tunneled, subcutaneously and connected to a Microject PCEA pump (Codman, Raynham, MA, USA) and reservoir bag containing preservative-free morphine 0.5 mg/mL. The pump was programmed to deliver a basal rate of 0.5 mL/hr. The bolus dose was 0.2 mL with 60 minute lock-out interval. The patient was instructed how to operate the infusion pump before discharging home. During the following 2 weeks, she reported more than 90% reduction of her low back and leg pain. She only had to use the on-demand bolus doses averaging 2 - 3 times a day. She was able to wean off her oral opioids completely. However, she developed bilateral leg edema and gained over 12 pounds during the 2-week infusion trial, despite wearing elastic stockings and keeping her legs elevated whenever possible. She did not experience any other significant side effects. Her edema finally resolved 2 days after termination of the epidural infusion. CONCLUSION Peripheral edema may occur and persist during epidural morphine infusion. This report represents the first case report, to the best of our knowledge, describing severe peripheral edema in an otherwise healthy patient while on epidural morphine administration during an outpatient epidural morphine infusion trial. This case report shows that continuous epidural morphine infusion, even in small dose, may cause peripheral edema in some patients.