Conditioning Electrical Stimulation to Improve Outcomes in Carpal Tunnel Syndrome

Background: Carpal tunnel syndrome (CTS) is the most common compression neuropathy, with a population prevalence of 3%. One quarter of these patients have severe symptoms that necessitate surgical release. Our lab has previously demonstrated that electrical stimulation (ES) at 20Hz for 1 hour immediately following carpal tunnel release significantly improved terminal motor latency, sensory nerve conduction (1). Postoperative electrical stimulation enhances regeneration locally at the site of injury(2); by contrast, the conditioning lesion improves the rate of regeneration along the entire distal stump. The traditional conditioning lesion refers to a purposeful crush injury delivered to a nerve prior to its transection and repair. Despite 40 years of promising research at the bench, describing the conditioning lesion as an effective method of promoting regeneration and reinnervation in an animal model, translation to the bedside until recently has been impossible due to its injurious nature (3). Our laboratory has recently identified conditioning electrical stimulation (CES) as an effective method of enhancing axonal regeneration, and improve motor and sensory reinnervation (4). Investigators of this study have further shown that CES improves regeneration and sensorimotor reinnervation beyond that attainable by postoperative CES (unpublished data). As such preoperative CES is potentially a clinically feasible method of improving patient outcomes.

Hypothesis: ES delivered prior to carpal tunnel release will improve functional outcomes in patients with severe carpal tunnel syndrome.

Research Methods: Plastic surgeons in the Division of Plastic Surgeon will identify patients with severe carpal tunnel syndrome and obtain their consent to be considered for inclusion in this study. Inclusion criteria includes patients aged over 18 years who have failed conservative treatment, who are found to have severe carpal tunnel syndrome on nerve conduction studies (thenar motor unit loss minimum two standard deviations between the mean for the age group). Exclusion criteria includes patients with pre-existing peripheral neuropathies. Patients will be randomized to three treatment groups: a) CES, b) postoperative ES, and c) no ES. Carpal tunnel release will be performed by a plastic surgeon in the standard fashion without neurolysis of the median nerve.

In clinic, skin will be cleansed with alcohol and a small gauge needle will be placed percutaneously in the proximal forearm, along the course of the median nerve based on known surface anatomy. This needle will be connected to the cathode of an SD-9 Grass stimulator. The anode will be attached to an electrical cable placed more distally on the forearm. Stimulation protocol will be based on that traditionally used for postoperative ES: 20 Hz of continuous stimulation for one hour, with voltage titrated to maximize voltage without causing patient discomfort. At the completion of one hour, the needle will be removed. One week later, carpal tunnel release will be performed by the plastic surgeon per standard technique, without neurolysis of the median nerve. Among patients receiving postoperative ES, the cathode will be placed next to the median nerve proximal to the carpal tunnel at the time of surgical release, and electrical stimulation upon completion of the surgery will follow the same stimulation parameters as outlined for CES.

Primary outcomes include sensory testing (two-point discrimination, Semmes-Weinstein monofilament, and cold threshold), motor testing (Purdue Pegboard Test), and patient-reported outcomes (Disabilities of the Arm, Shoulder and Hand questionnaire). These are well established standard testing modalities for assessing recovery following carpal tunnel release (5). Scores for two-point discrimination range from 1 to 20 mm with smaller distance reflecting better hand sensibility. Mean score for the Purdue Pegboard Test in health control is 12 pegs with a greater number reflecting better hand dexterity. Range of score for the DASH questionnaire is 0 to 100 with a higher number representing greater disability. Testing will be performed preoperatively to establish baseline sensorimotor function, then postoperatively at 3, 6, and 12 months. Outcome measures will be analyzed using two-way ANOVA, with post-hoc analysis of significant association (p<0.05).

Justification: Recovery following surgical release in severe carpal tunnel is often incomplete, with persistent motor and sensory deficits. While postoperative ES improves regeneration, functional deficits persist; however, these studies have established ES as safe and well-tolerated by patients. By changing the timing of ES from postoperative to preoperative CES, animal data suggests functional outcomes can be further improved by upregulating regenerative pathways to maximize the rate of axonal extension. As CES can be delivered percutaneously in the clinic at the initial of initial assessment, prior to surgical release, this technique is both safe, clinically feasible and may significantly improve the outcomes of patients with compression neuropathies.