A modified multiple point stimulation method for motor unit number estimation of the hypothenar muscles.

INTRODUCTION: The goal of this study is to test the hypothesis that single motor unit action potentials (SMUPs) originating from other ulnar nerve-innervated intrinsic hand muscles can inflate the motor unit number estimation (MUNE) of the hypothenar muscles. METHODS: Using the multiple point stimulation method, SMUPs recorded over the hypothenar muscles from distant origins were characterized through multichannel recordings. The MUNE calculated using only the hypothenar SMUPs was compared with estimations based on the whole ensemble. RESULTS: Of the 41 studies performed, distant SMUPs represented 17 ± 9.5% (mean ± SD) of the overall sample. MUNE calculated using only hypothenar SMUPs was 423 ± 204, compared with 537 ± 290 if all SMUPs were included (P < 0.05). The extent of increase in MUNE was highly correlated with the proportion of distant SMUPs found (r = 0.89, P < 0.05). DISCUSSION: Erroneous inclusion of SMUPs from distant muscles can significantly distort the MUNE results. Muscle Nerve 59:337-341, 2019.

Intraoperative Brief Electrical Stimulation of the Spinal Accessory Nerve (BEST SPIN) for prevention of shoulder dysfunction after oncologic neck dissection: a double-blinded, randomized controlled trial.

BACKGROUND: Shoulder dysfunction is common after neck dissection for head and neck cancer (HNC). Brief electrical stimulation (BES) is a novel technique that has been shown to enhance neuronal regeneration after nerve injury by modulating the brain-derived neurotrophic growth factor (BDNF) pathways. The objective of this study was to evaluate the effect of BES on postoperative shoulder function following oncologic neck dissection. METHODS: Adult participants with a new diagnosis of HNC undergoing Level IIb +/- V neck dissection were recruited. Those in the treatment group received intraoperative BES applied to the spinal accessory nerve (SAN) after completion of neck dissection for 60 min of continuous 20 Hz stimulation at 3-5 V of 0.1 msec balanced biphasic pulses, while those in the control group received no stimulation (NS). The primary outcome measured was the Constant-Murley Shoulder (CMS) Score, comparing changes from baseline to 12 months post-neck dissection. Secondary outcomes included the change in the Neck Dissection Impairment Index (ΔNDII) score and the change in compound muscle action potential amplitude (ΔCMAP) over the same period. RESULTS: Fifty-four patients were randomized to the treatment or control group with a 1:1 allocation scheme. No differences in demographics, tumor characteristics, or neck dissection types were found between groups. Significantly lower ΔCMS scores were observed in the BES group at 12 months, indicating better preservation of shoulder function (p = 0.007). Only four in the BES group compared to 17 patients in the NS groups saw decreases greater than the minimally important clinical difference (MICD) of the CMS (p = 0.023). However, NDII scores (p = 0.089) and CMAP amplitudes (p = 0.067) between the groups did not reach statistical significance at 12 months. BES participants with Level IIb + V neck dissections had significantly better ΔCMS and ΔCMAP scores at 12 months (p = 0.048 and p = 0.025, respectively). CONCLUSIONS: Application of BES to the SAN may help reduce impaired shoulder function in patients undergoing oncologic neck dissection, and may be considered a viable adjunct to functional rehabilitation therapies. TRIAL REGISTRATION: Clinicaltrials.gov ( NCT02268344 , October 17, 2014).

Test--retest reliability of a modified multiple point stimulation technique for motor unit number estimation.

OBJECTIVE: Multiple point stimulation (MPS) is a widely used technique to estimate the number of motor units in a muscle. Test-retest reliability must be high for the motor unit number estimates to be clinically useful. We hypothesized that the reliability of MPS can be improved by using a long stimulus pulse width (1ms), in addition to the standard 0.05ms pulse width. METHODS: Median nerve innervated thenar muscles were examined in 11 young subjects, 27+/-3 (mean +/-SD) years old and in 5 elderly subjects, 71+/-11 years old. The experimenter conducted the studies twice on each subject. RESULTS: Test-retest reliability, using the modified MPS technique, was substantially higher (Cronbach's alpha of 0.88) than using the standard method (Cronbach's alpha of 0.80) in the young subjects. In contrast, for the elderly subjects the test-retest reliability of MUNE was high for both the modified technique (Cronbach's alpha of 0.96) and the standard technique (Cronbach's alpha of 0.99). CONCLUSIONS: Test-retest reliability of MPS can be significantly improved by using a long stimulus pulse width and the standard stimulus pulse width in younger subjects. However, this is not necessary in elderly subjects. SIGNIFICANCE: The greater reliability of this modified MPS method should enhance its clinical utility.

Compression of the ulnar nerve at the elbow by an intraneural ganglion.

A rare cause of ulnar nerve compression at the elbow is presented in this report. A 42 year old right-handed mechanic developed subacute, progressive numbness, tingling and weakness in his right hand. Electrophysiologic studies demonstrated a severe conduction block affecting the ulnar nerve in the retrotrochlear groove but without any sign of major axonal loss. His hand functions were carefully studied prior to surgery. While fine motor tasks were not affected, the hand strength was markedly diminished. At surgery, a 1-cm diameter intraneural ganglion at the site of the conduction block was found and excised. The patient made a dramatic recovery within 6 weeks post-surgery. The conduction block completely resolved and the hand functions also returned to normal. This and other reported cases point to the importance of early diagnosis and intervention.

Use of the collision technique to improve the accuracy of motor unit number estimation.

OBJECTIVE: To evaluate the risk of stimulating the same motor axon at different points along the median nerve when using the multiple point stimulation (MPS) technique and how this affects the accuracy of the motor unit number estimate (MUNE). METHODS: Using the MPS technique, MUNE in the median innervated intrinsic hand muscles was done on two normal subjects, a patient with carpal tunnel syndrome and one with prior poliomyelitis. The collision technique was then used to confirm whether two motor unit action potentials (MUAPs) with similar configurations and sizes were generated by the same motor unit. A new MUNE was recalculated after the repeated inclusion of the same motor unit had been excluded. RESULTS: While the risk of stimulating the same motor axon at widely separate locations of the median nerve was negligible in normal subjects, this risk was much higher in patients with a depleted motor neuron pool. This resulted in marked distortion of the calculated size of the average single MUAP and, consequently, inaccuracy of the MUNE. CONCLUSIONS: The inadvertent inclusion of the same motor units, if not recognized, can markedly affect the accuracy of the MUNE. The collision technique can be useful in minimizing this risk.