Peripheral Neuromodulation to Treat Postamputation Pain.

Some of the more common peripherally mediated pain disorders are postamputation stump pain and phantom pain. These disabling conditions have proven difficult to treat. Here we aim to illustrate an option to treat postamputation pain using peripheral neurostimulation techniques. Traditional peripheral neuromodulation techniques use standard stimulation parameters and work by stimulation of nerve tissues which are then felt by the patient as a tingling sensation or paresthesia. Recently introduced high-frequency (10 kHz) electrical nerve block [HFAC (high-frequency alternating current) block] via a surgically implanted peripheral nerve cuff electrode results in true conduction block which actually blocks action potentials emanating from the painful neuroma and thus suppresses pain without tingling or paresthesia felt by the patient. In a recently completed 10-patient pilot study, the average pain level decreased from a score of 5.7 to 1.4 (out of 10) after HFAC block therapy with 85% of all testing sessions yielding a >50% pain reduction; a very significant reduction in the use of opioid and other analgesics was also noted, with all tested patients either stopping or decreasing their analgesic intake significantly. Patients achieved meaningful and significant pain reduction throughout the study, and patients who had phantom pain (in addition to stump pain) that responded to local anesthetic injections also responded favorably with HFAC block, presumably because in these particular patients, the phantom symptoms were peripherally generated. Each of the tested patients reported that HFAC block provided the most significant amount of pain reduction they had ever experienced when compared to other pain modalities tried since their amputations. The high-frequency electric nerve block technique is currently investigational pending FDA clearance. The next step for this modality is a pivotal trial, with the goal of having this therapy available to the mass market upon FDA clearance.

High-frequency electrical nerve block for postamputation pain: a pilot study.

OBJECTIVES: This study aimed to assess the analgesic effect of kilohertz alternating current applied to the severed nerves in amputees afflicted by intractable limb pain. METHODS: Ten lower-limb amputees with chronic and severe residual limb pain or phantom limb pain who attained significant pain reduction after local nerve block injection were enrolled. A cuff electrode was wrapped around the sciatic or tibial nerve. An external waveform generator was used for the main part of the study, while an implantable generator was developed and implanted in the responders after 9 to 12 months. Sinusoidal waveforms of 10 kHz and up to 10 V were applied for 30 min during each subject-initiated treatment session. A diary was used to record pain intensities before and after each session. RESULTS: Among the seven subjects who received treatment, the average pain reduction was 75% at the three-month primary end point. These subjects were responders per predefined criterion of achieving ≥50% pain reduction in ≥50% of treatment sessions for the three-month end point. Pain medication use and interference of pain on functions was significantly reduced. The treatment efficacy was sustained through the follow-up period of up to 12 months. Besides dislodgement and loss of function for one electrode in one subject, all other devices functioned as intended. No changes of residual motor and sensory function were observed. CONCLUSION: This pilot study generated preliminary evidence on the efficacy and safety of kilohertz electrical nerve block for postamputation pain, justifying a pivotal study for regulatory approval.