medwireNews: Ambulatory continuous peripheral nerve block (CPNB) may be an effective treatment for phantom limb pain (PLP), results of a pilot study indicate.
As there is currently no reliable treatment for PLP, the novel approach should be evaluated in a larger trial, say Brian Ilfeld (University of California, San Diego, USA) and fellow researchers.
Ilfeld's group hypothesized that as chronic PLP may be maintained from abnormal peripheral input, a CPNB given over an extended period may permanently reorganize cortical pain mapping and provide lasting analgesia.
"Imaging techniques such as functional magnetic resonance imaging have documented a correlation between PLP and cortical reorganization - with the most intense phantom pain provoking the greatest cortical changes," explain the authors.
"The abnormal mapping-and PLP-that occur with amputation are not necessarily fixed and may be dependent on signaling from the peripheral nervous system."
To investigate, the researchers recruited three men with intractable PLP following below-the-knee or below-the-elbow amputations. They were randomly assigned to receive a perineural infusion of either ropivacaine 0.4% or saline placebo delivered over 6 days via either femoral/popliteal-sciatic or infraclavicular perineural catheters. Four months later, the participants received an infusion of the alternative (crossover) treatment.
By chance, all three men received saline at the first infusion. None reported any change in their pain severity or incidence during or after this infusion.
Two men subsequently received an infusion of ropivacaine. Both men reported an immediate and complete resolution of their PLP, with their pain scores dropping to 0 on a numeric rating scale of 0-10.
The men were followed up for 52 weeks. During this time, one man reported no recurrence of his PLP whatsoever while the other man reported approximately one episode per week of mild PLP, which was a marked improvement on his pretreatment pain levels in terms of both frequency and severity.
The nerve block was not associated with any procedural complications or adverse events.
Writing in Pain Medicine, Ilfeld and co-authors conclude: "These results may have major clinical implications given the 1.6 million people currently living with an amputated limb in the United States alone; high prevalence of PLP following amputation; decrease in quality-of-life associated with PLP; and the dearth of reliable treatments for this ailment.
"However, a large, randomized, controlled clinical trial is required to investigate treating intractable PLP with CPNB in order to draw definitive conclusions."