Application of pulsed radiofrequency currents to rat dorsal root ganglia modulates nerve injury-induced tactile allodynia.

BACKGROUND: Application of pulsed radiofrequency (PRF) currents to the dorsal root ganglia (DRG) has been reported to produce relief from certain pain states without causing thermal ablation. In this study, we examined the direct correlation between PRF application to DRG associated with spinal nerve injury and reversal of injury-induced behavioral hypersensitivity in a rat neuropathic pain model. METHODS: Neuropathic lesioning was performed via left L5 spinal nerve ligation on male adult Sprague-Dawley rats. Once the injured rats had developed tactile allodynia, one group was then assigned to PRF treatment of the L5 DRG and another group was assigned to the sham treatment to the DRG. Behavioral testing was performed on both the control and treated paws using the von Frey filament test before the surgery and at indicated days. The resulting data were analyzed using a linear mixed model to assess the overall difference between the treatment groups and the overall difference among the study days. Cohen's d statistic was computed from paired difference-from-baseline scores for each of the 14 study days after treatment and these measures of effect size were then used to descriptively compare the recovery patterns over time for each study group. RESULTS: Spinal nerve injury resulted in the development of behavioral hypersensitivity to von Frey filament stimulation (allodynia) in the hindpaw of the left (injury) side. Mixed linear modeling showed a significant difference between the treatment groups (P = 0.0079) and a significant change of paw withdrawal threshold means over time (P = 0.0006) for all 12 animals. Evaluation of Cohen's d (effect size) revealed that the PRF-treated animals exhibited better recovery and recorded larger effect sizes than the sham-treated animals on 10 of the 14 post-PRF treatment days and exhibited moderate-to-strong effects posttreatment at days 8 to 10 and at and beyond day 32. CONCLUSIONS: Findings from this study support that PRF of the DRG causes reversal of nerve injury (spinal nerve ligation)-induced tactile allodynia in rats. This allodynia reversal indicates that nonablative PRF acting via modulation of the DRG can speed recovery in nerve injury-induced pain.

False positive radiographical evidence of pump catheter migration into the spinal cord.

Intrathecal drug delivery systems are becoming an increasingly common modality used by physicians to treat patients. Specifically, chronic spasticity secondary to multiple sclerosis (MS) may be treated with intrathecal baclofen (ITB) therapy when oral antispasmodics do not provide adequate relief. ITB therapy is effective, localizes drug delivery, and does not have the same degree of intolerable systemic effects often seen with oral and parenteral medications. As the use of intrathecal drug delivery systems has become more common, so has the incidence of adverse events. ITB administration requires the surgical implantation of indwelling catheters and a pump reservoir. Although this therapy is useful in treating spasticity, risks unique to intrathecal drug delivery systems include medication dosing errors, pump malfunction, infection, and catheter breakage or dislocation. To our knowledge intrathecal pump catheter migration into the spinal cord is a very rare complication with only 2 such complications reported. We present a case of an intrathecal baclofen pump catheter that was initially believed to have migrated into the spinal cord and the innovative use of cinefluoroscopy and digital subtraction used to identify catheter placement. Moreover, after confirmation of the catheter position within the spinal cord on magnetic resonance imaging (MRI) our team elected to perform a laminectomy, which demonstrated that the catheter was not in the spinal cord but was surrounded by arachnoid adhesions. We hope our efforts will provide the clinician insight into the common difficulties that arise and how best to troubleshoot them to serve this specific patient population and prevent potentially life-threatening complications.