Priapism--a rare complication following continuous epidural morphine and bupivacaine infusion

Abstract

Background: Intraspinal drug delivery (IDD) therapy has been increasingly used in patients with intractable, nonmalignant pain who fail to respond to conventional treatment or can not tolerate systemic opioid therapy due to side effects. By infusing a small amount of analgesics directly into the cerebrospinal fluid (CSF) in close proximity to the receptor sites in the spinal cord, one is able to achieve the spinally mediated analgesia, sparing side effects ffrom 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 functional opioid infusion trial versus an inpatient trial is that it more closely mimics what the patient does in his or her usual activities of daily living, therefore minimizing the false positive rate of the inpatient screening trial.

Objective: To describe a rare complication, priapism, observed during an outpatient continuous epidural morphine and bupivacaine infusion trial.

Case report: A 49-year-old male with intractable, chronic low back pain due to diffuse lumbar degenerative disc disease, lumbar spondylosis referred to our clinic for consideration of IDD therapy, after failing to respond to multi-modality pain management including medications, physical therapy with modality, transcutaneous nerve stimulation (TENS), and various interventional procedures. Following a pre-implant psychological evaluation, he was scheduled for the outpatient epidural morphine and bupivacaine infusion trial. A tunneled lumbar epidural a catheter was placed at L3-L4 with the catheter tip advanced to L1 under fluoroscopic guidance. 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 0.4 mg/mL and bupivacaine 0.016%. The pump was programmed to deliver a basal rate of 0.5 mL/h. The bolus dose was 0.2 mL with a 60-minute lock out interval. The patient was instructed how to use the pump properly before discharging home. Two hours following the initiation of infusion trial, the patient started to experience penile erection. It was initially painless, but became progressively painful and intensified. The unremitting priapism lasted 8 hours, finally resolving 2 to 3 hours after discontinuing the infusion. The patient recovered fully without any sequelae.

Conclusion: Priapism may occur as a rare complication following epidural morphine administration. This report represents the third case report thus far in the literature revealing priapism induced by epidural morphine administration, yet, it is the only report, to our knowledge, describing priapism occurring in a patient undergoing an outpatient epidural morphine and bupivacaine infusion trial. We believe that epidural morphine, rather than bupivacaine, is responsible for causing priapism in this patient, through a yet to be defined spinal mechanism.