Boon, Andrea J.

ABSTRACT Introduction/Aims Phrenic nerve conduction studies (NCS) are regularly used in the evaluation of neuromuscular respiratory dysfunction; however, the impact of body mass index (BMI) on phrenic compound muscle action potential (CMAP) amplitudes remains poorly characterized. We evaluated the relationship between BMI and phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Methods We performed a retrospective secondary analysis of patients derived from two previously published cohorts from Mayo Clinic (Rochester, Minnesota) and the University of Alberta (Edmonton, Alberta) evaluating diaphragm ultrasound in suspected neuromuscular respiratory insufficiency. Patients without evidence of neuromuscular disease affecting the diaphragm who underwent bilateral phrenic NCS and diaphragm ultrasound were included. Results Seventy‐nine patients met inclusion criteria, including 36 with BMI ≥ 30 kg/m 2 . Median phrenic CMAP amplitudes were significantly lower in patients with BMI ≥ 30 kg/m 2 compared to BMI < 30 kg/m 2 (0.25 mV [ IQR 0.10–0.38] vs. 0.50 mV [0.30–0.65], p < 0.001). Low phrenic CMAP amplitudes (< 0.3 mV ) were more common in patients with obesity (58% vs. 21%, p < 0.001). BMI demonstrated a moderate negative correlation with phrenic CMAP amplitude ( ρ = −0.50, p < 0.001). Diaphragm thickness at functional residual capacity did not differ significantly between BMI groups, while diaphragm thickening ratio was modestly lower in obesity. Discussion Elevated BMI is associated with lower phrenic CMAP amplitudes in patients without evidence of neuromuscular diaphragmatic dysfunction. Reduced phrenic CMAP amplitudes in obesity may reflect technical recording limitations rather than clinically meaningful diaphragmatic dysfunction. Low‐amplitude phrenic responses in patients with obesity should be interpreted cautiously and alongside adjunctive assessments such as diaphragm ultrasound.

Purpose: Hereditary transthyretin amyloidosis (ATTRv) is a progressive multisystem disease in which median mononeuropathy at the wrist (MNW) is common and often precedes systemic involvement. Nerve conduction studies (NCS) have historically been the gold standard for MNW, but neuromuscular ultrasound (NMUS) is complementary. The aim of this study was to compare NMUS with electrodiagnostic (EDX) testing for the diagnosis of MNW in patients with symptomatic ATTRv. Methods: A retrospective review was performed of patients 18 years and older with ATTRv confirmed by genetic testing who underwent both EDX testing and NMUS of the median nerve between 2019 and 2025. Demographic, NMUS, and EDX data were collected. Results: Data from 15 upper limbs in 10 patients were analyzed. Median nerve cross‐sectional area at the wrist was significantly greater than reference values ( P = 0.041). MNW was identified in 80% of wrists by NMUS and 100% by NCS, with no significant difference between modalities. Median nerve cross‐sectional area at the wrist did not significantly correlate with MNW severity determined by NCS ( r = −0.018; P = 0.941) or with any NCS parameters (all P > 0.080). Concurrent polyneuropathy was diagnosed in 60% of patients, but there was no association between polyneuropathy and MNW detection by either modality ( P > 0.197). Conclusions: NMUS and NCS demonstrate comparable diagnostic accuracy for MNW in ATTRv. Given its noninvasive nature and efficiency, NMUS may serve as an adjunct to classic EDX testing in this population.

ABSTRACT Introduction/Aims Ultrasound (US) guidance may be essential for accurate electromyography (EMG) needle placement in less‐commonly evaluated muscles, such as the extensor carpi radialis longus (ECRL) and brevis (ECRB), and particularly for identifying suitable donor muscles prior to tendon transfers to restore upper extremity function. Our primary aim was to compare the accuracy of trainee palpation‐guided versus first‐attempt US‐guided needle placement. Our secondary aim was to describe the locations of inaccurate needle placement. Methods Seven subjects each performed four needle placements (ECRL and ECRB, both palpation‐guided and US‐guided), totaling 28 placements into a cadaveric specimen. US‐guided needle placement was performed with one attempt after one live demonstration. Results No palpation‐guided ECRL attempts were accurate while only two of the palpation‐guided ECRB attempts were accurate. First‐attempt US‐guided needle placement was significantly more accurate overall (64.3% vs. 14.2%, p = 0.020), and specifically for ECRL (71.4% vs. 0%, p = 0.025). Combining palpation‐guided ECRL and ECRB attempts, the needle was inadvertently placed in the extensor digitorum communis (50%), extensor carpi ulnaris (16.7%), and brachioradialis (16.7%). Both US‐guided ECRL‐intended errors involved placing the needle into the adjacent ECRB. Discussion This study suggests that EMG needle placement into ECRL and ECRB by trainees may be more accurate with US guidance. Accurate preoperative individual needle assessments of both wrist extensors are essential for patients with tetraplegia considering reconstructive surgery to restore functional grasp and should be performed with US guidance.

ABSTRACT Introduction/Aims Patients with cervical spinal cord injury (SCI) prioritize recovery of upper extremity function. Upper extremity reconstruction can restore function in carefully selected individuals. Infralesional cord damage, observed below the neurological level of injury (NLI), may affect postoperative outcomes. We characterized the extent of infralesional lower motor neuron (LMN) injury in patients with traumatic cervical SCI. Methods Each patient underwent electromyography (EMG) of potential donor and recipient muscles based on preoperative clinical evaluation and specific candidacy for nerve and/or tendon transfers. The presence of infralesional pathologic insertional activity (IA), reduced motor unit potential (MUP) recruitment and/or neurogenic MUPs was assessed. The caudal‐most segment with infralesional LMN injury was determined. Inclusion criteria were patients with (1) traumatic cervical SCI; (2) injury ≥ 3 months duration; (3) preoperative planning EMG for nerve and/or tendon transfers. Results Forty‐eight upper extremity EMGs in 25 patients (68% male; mean age 39.5 years at injury) with traumatic cervical SCI were included. The NLI was at C7 or above in each patient, and 64% of SCIs were motor complete. Infralesional EMG abnormalities (median time from injury to EMG 466 days) were found a median of 3.0 (IQR 3.0–4.0) segments below the NLI. Three patients with an NLI as rostral as C1–C2 exhibited LMN injury seven segments below the NLI. Discussion In persons with traumatic cervical SCI, evidence of LMN injury may be observed several segments below the NLI. Defining the true extent of LMN involvement directly informs timing and selection of reconstructive procedures to maximize functional recovery.

Purpose: Neuromuscular ultrasound, including cross-sectional area measurements, adds diagnostic value to the clinical and electrodiagnosis evaluation of ulnar neuropathy at the elbow. Previously published reference values for ulnar nerve size vary widely. Our objective was to establish age-specific reference values for ulnar nerve cross-sectional area at multiple sites in asymptomatic adults for our laboratory. Methods: Healthy adult subjects without neuromuscular symptoms or disease were recruited from our tertiary referral electromyogram laboratory and staff. Ulnar nerve cross-sectional area measurements were made in short axis at the wrist, forearm, cubital tunnel, retrocondylar groove, 2 cm proximal to the medial epicondyle, and mid-upper arm with the elbow flexed to 90°. Dynamic neuromuscular ultrasound evaluated for subluxation and dislocation at the medial epicondyle. Results were stratified by age group (younger than 40, 40–60, and older than 60 years) with at least 20 subjects per sex per group, as well as by sex, body mass index, and handedness. The upper limit of normal was established as two standard deviations above the mean. Results: One hundred forty-two subjects (ages 18–84, mean 47.7 years) were included. Cross-sectional area significantly increased with age at all sites except the wrist. Cross-sectional area cut-offs at the retrocondylar groove were 10.0, 10.9, and 11.4 mm 2 , respectively, by age group. Ratios comparing retrocondylar groove and cubital tunnel to arm and forearm were calculated. Thirty-two percent had subluxation or dislocation in at least one limb. Conclusions: Age-specific cross-sectional area cut-offs and ratios may facilitate a more nuanced interpretation and diagnostic value when used in conjunction with clinical and electrodiagnosis evaluation of ulnar neuropathy at the elbow.

ABSTRACT Introduction/Aims Neuromuscular ultrasound (NMUS) is becoming increasingly incorporated as a complementary tool in electrodiagnostic (EDX) medicine. Competency assessment is critical to ensure adequate quality, appropriate application, and accurate interpretation. The primary objective was to develop a competency‐based assessment tool of foundational NMUS skills among postgraduate medical trainees in a single center. Methods The assessment included written (28 multiple‐choice, short answer, or yes/no) questions and practical skills (15 prompts) sections recommended by a published consensus‐based survey to include the knowledge and skills necessary to achieve minimal competency for unsupervised practice of NMUS for common conditions. The written portion included interpretation of basic pathology. Core practical content focused on the most evaluated structures in the Mayo EDX laboratory: the median and ulnar nerves and diaphragm muscle. The practical portion was administered by a single examiner and scored with a five‐point competency‐based rating. Four experienced educators used the Angoff standard setting method to set passing scores for each section. Results Subjects included three EMG‐track clinical neurophysiology fellows who completed a NMUS lecture series with supervised hands‐on scanning and a 2‐week intra‐lab NMUS elective during fellowship. Composite scores ranged from 89% to 97%. All subjects met minimum passing scores for each section (77% and 88% for the knowledge and skills sections, respectively). Discussion This NMUS competency assessment was successfully implemented and may be incorporated into postgraduate medical trainee evaluation to ensure minimal competency in evaluation of carpal tunnel syndrome, ulnar neuropathy at the elbow, and diaphragm function. This effort integrates quality NMUS evaluations into clinical practice.

ABSTRACT Introduction/Aims Accurate needle electromyography (EMG) of the short head of the biceps femoris (SHBF) is often important to localize nerve damage when proximal to the fibular head. Techniques have been proposed for accurate SHBF EMG; however, needle placement accuracy is low and with the risk of inadvertent needle placement into the long head (LHBF) potentially resulting in false localization and inappropriate operative management. This study aimed to define the optimal window for accurate SHBF needle EMG placement through ultrasound (US) investigation of the anatomical relationships of the SHBF, LHBF, and common fibular nerve (CFN) in the distal posterolateral thigh. Methods Forty lower limbs from 20 healthy adults were evaluated using US. Distances from the popliteal crease (PC) to the SHBF and LHBF myotendinous junctions and position of the CFN in the popliteal fossa were recorded. The “SHBF window” was defined as the region where the SHBF muscle body is present in the absence of the LHBF. Results The SHBF was located anterolateral to the LHBF tendon/muscle and the CFN medial to the SHBF in all limbs. The average distances from the PC to SHBF and LHBF muscles were 0.6 and 6.4 cm, respectively. The optimal “SHBF window” was identified to be 3–4 cm (2–3 fingerbreadths) proximal to the PC, anterolateral to the LHBF tendon in the distal thigh. Discussion SHBF examination within this optimized window results in increased accuracy of needle placement, aiding in the electrodiagnostic localization of fibular nerve lesions.

ABSTRACT Introduction/Aims Ultrasound (US) guidance may ensure proper needle placement during electromyography (EMG) when assessing for suitable donor muscles for upper limb reconstruction. A distinct intermuscular fascial border aids in delineating the separation between the brachioradialis (BR) and extensor carpi radialis longus (ECRL) muscles. However, this border may be absent, making correct needle placement complex and assessment more difficult. The purpose of this study was to describe the presence and absence of this fascial border in healthy individuals to help with accurate EMG needle placement. Methods Twenty healthy patients underwent sonographic examination by a single sonographer physician of the ECRL and BR to identify the presence or absence of the intermuscular fascial border. Results The fascial border that routinely separates the ECRL and BR was absent in at least one arm in 20% of subjects (12.5% of upper limbs). One subject had an absent fascial border in both upper limbs. Discussion US can assess for the presence or absence of intermuscular fascial borders. This assessment is important for accurate EMG needle placement and localization. While the clinical significance of an absent ECRL‐BR fascial border is currently unknown, future studies should examine the effect of absent ECRL‐BR fascial borders on wrist extension.

ABSTRACTIntroduction/AimsNeuromuscular ultrasound (NMUS), initially performed by physicians, is increasingly performed by technicians in many electrodiagnostic (EDX) laboratories for certain studies under physician supervision. The aims of this study were to determine: (1) the reproducibility of nonphysician sonographers' assessments of the median nerve and (2) the need for ongoing training to maintain the reproducibility and reliability of median nerve ultrasound assessments.MethodsThe median nerve was examined sonographically in a healthy volunteer by 12 nonphysicians on 3 separate occasions: Day 1 and then 2 weeks (Day 2) and 4 months (Day 3) later. Cross‐sectional area (CSA) and wrist‐to‐forearm ratios (WFRs) were calculated each time. Sonographers were retrained prior to Day 2. Reproducibility and reliability were determined using coefficients of variation calculated for each characteristic for each day and each nonphysician sonographer, comparing performance across the 3 time points.ResultsThere was overall less variation for each characteristic (wrist CSA, forearm CSA, and WFR) on Day 2 compared to Day 1 (coefficients of variation 3.0%, 5.4%, and 5.7% vs. 8.8%, 15.5%, and 11.3%, respectively), both when viewed at the group and individual levels, indicating an improvement in reproducibility and reliability after the retraining session. The improvement was similar for Day 3.DiscussionThis study demonstrates the need for training and subsequent retraining sessions to ensure the reproducibility and reliability of NMUS measurements in the median nerve.