Screening of Axonal Degeneration in Carpal Tunnel Syndrome Using Ultrasonography and Nerve Conduction Studies

Here we present a protocol using nerve conduction studies and ultrasound to screen potential axonal degeneration associated with carpal tunnel syndrome. The criteria for differentiation are established. Compared to conventional approaches, this method is noninvasive, convenient, and efficient, with an overall satisfactory accuracy, sensitivity, and specificity.

This non invasive approach using nerve conduction studies and ultrasound is used to specifically and sensitively assess the axonal degeneration in carpal tunnel syndrome patients. This method can be used by clinicians to directly assess the pathological stage of the disease, and can be easily applied for better treatment region planning. Demonstrating the procedure will be Phoebe Chau, an enrolled nurse, and Kwok-Pui Leung, a physician, both from my laboratory.

To measure the conduction in the median sensory nerve, first have the patient wash their hands with warm water. After drying, place the recording ring electrode at the proximal interphalangeal joint, and the reference ring electrode over the distal interphalangeal joint. Place the other recording electrodes at the wrist, between the tendons of the flexor carpal radialis, and the palmaris longus.

12cm proximal to the recording ring electrode, and ideally proximal to the distal wrist crease. After making sure that the ground electrode is between the stimulation and recording sites, apply super maximal stimulus 10 times to the median nerve via the attached electrodes over the index finger. To measure the conduction in the ulnar sensory nerve, place the recording ring electrode halfway on the proximal phalanx of the 5th digit, and the reference ring electrode 4cm distal to the recording ring electrode.

Place the other recording electrodes near the tendon of the flexor carpi ulnaris, 12cm proximal to the recording ring electrode, making sure the ground electrode is between the stimulation and recording sites. Then apply a super maximal stimulus 10 times to the ulnar nerve via attached electrodes over the 5th finger. To measure the conduction in the median motor nerve, place the recording ring's electrode in the most prominent eminence of the thenar area at the motor point of the abductor pollicis brevis, and place the reference ring electrode on the proximal phalanx of the thumb.

Then use an electronic stimulator to stimulate at the mid-palm, three to four centimeters distal to the distal wrist crease, and 6.5 centimeters proximal to the recording ring electrode at the wrist, between the tendons of the flexor carpi radialis and the palmaris longus. In the medial aspect of the antecubital space of the elbow, just lateral to the brachial artery. To measure the conduction in the ulnar motor nerve, place the recording ring electrode over the belly of the abductor digiti minimi.

The reference ring electrode to the distal phalanx of the 5th digit, and the ground electrode, between the stimulation and the recording sites. Then stimulate at the wrist, 7cm proximal to the recording ring electrode, just lateral or medial to the flexor carpi radialis tendon. Below and above the elbow, 5cm distal and proximal to the ulnar groove.

For ultrasound measurements, seat the patient on a plinth with their hands resting in a horizontal supination position, and the fingers semi extended. Place some ultrasound gel over the probe of the transducer, the wrist site, and the distal 1/3 forearm. Next, use a 13 to 14 megahertz linear array transducer to perform a transverse scan at the inlet of the carpal tunnel.

Freeze the real time imaging and continuously caliper the hyperechoic epineurium of the median nerve at the inlet of the carpal tunnel. Then scan proximally along the innervated area of the median nerve to the site of the 1/3 distal forearm. Freeze the real time imaging, and caliper the hyperechoic epineurium of the median nerve at the 1/3 distal forearm.

After screening for associated axonal degeneration, those patients with any ultrasound parameter values above the corresponding cutoff values are considered as suffering from the potential coexistence of axonal degeneration. Alternatively, the ultrasound readings can be considered as indicators of potential axonal degeneration, should the subject not fulfill the nerve conduction studies criteria. For example, in this representative study, significant differences were found between patients with demyelination and associated axonal degeneration, indicating that this protocol can be an effective tool in screening axonal degeneration associated with carpal tunnel syndrome.

Further, in this group of patients who did not fulfill the nerve conduction criteria and were enrolled with ultrasound measurements generated descriptively, the ultrasound measurement data suggested that all of these patients were potentially associated with coexisting axonal degeneration based on their ultrasound measurements alone. In nerve conduction study, sanitized chemical procedure, and side-to-side comparisons are both important as they can increase the reliability of the assessment. Although the tomography is the gold standard for confirming axonal degeneration, further validation study can be used to evaluate the reliability and validity between the tomography and our assessment package.

During the ultrasound assessment, make sure the ultrasound parameters are consistent and select the appropriate frequency and probe size. This technique path is the way for researchers to explore innovative uses of ultrasound for diagnosing carpal tunnel syndrome, and may have the potential to be used for predicting treatment effectiveness.