Thumbs up for electrodiagnosis in neonatal brachial plexopathy

Editorial: Despite remarkable advances in obstetrics, neonatal brachial plexus palsy (NBPP) remains a challenge for many families and treating physicians. Approximately 2 out of 1000 neonates experience traction of the brachial plexus and/or avulsion of its roots during birth, which localizes to the C5/C6 distribution in up to 80% of neonates. Fetal macrosomia, instrumented delivery, prolonged labor, shoulder dystocia, multiparity, gestational diabetes, and fetal distress are all predisposing factors. While the majority of patients recover with conservative treatment within the first few months, 20%–30% of patients’ conditions persist, necessitating microsurgery. Specific fetal, maternal, and perinatal variables, such as cephalic presentation, induction or augmentation of labor, birth weight >9 lbs, and the presence of Horner syndrome, significantly increase the odds of persistent deficits from NBPP at 1 year. There is currently no universally accepted management algorithm for NBPP. Most experts use clinical examination as the cornerstone of prognostication, with the lack of meaningful biceps function in the first 3–9 months of life prompting surgical intervention. Yet, when used as a single parameter, elbow flexion at 3 months incorrectly predicts recovery in 12.8% of patients. Given that the location and severity of neural injury determines the best course of action, several extra-operative (eg, nerve conduction studies [NCS], needle electromyography [EMG], computed tomography myelography [CTM], magnetic resonance imaging [MRI], and ultrasound [US]) and intra-operative (eg, direct visualization of the neural structures, nerve to muscle compound muscle action potentials [CMAPs], nerve to nerve action potentials [NAPs], somatosensory evoked potentials [SSEPs], and “neurogenic” motor evoked potentials [MEPs]) techniques have been used. Within the extra-operative ones, CTM is rapidly being replaced by MRI for intradural preganglionic evaluation, and US is being relied upon more heavily for extraforaminal postganglionic assessment. Among the intraoperative techniques, an absent NAP or CMAP was shown to predict a severe lesion such as neurotmesis or avulsion with a specificity of >0.9, although the sensitivity of an absent NAP or CMAP for predicting a severe lesion was typically <0.3. Thus, direct surgical exploration remains the gold standard. Nevertheless, pre-operative diagnostic information remains invaluable, and electrodiagnostic (EDX) testing plays a cardinal role. EDX testing is safe and feasible across the age spectrum and obviates the higher cost and risks of sedation that are commonly associated with the acquisition of the imaging modalities mentioned above in infants. Comparative studies have demonstrated better diagnostic accuracy of EDX testing in NBPP compared to neuroimaging techniques, particularly with regard to specificity and accuracy of identifying preganglionic injuries. Other studies have highlighted the prognostic value of serial EDX testing for determining the need for surgical repair. On the other hand, some investigators have expressed doubt about the accuracy (and hence necessity) of EDX testing in NBPP. That controversy may be partially explained by the relative paucity of available studies and the overall suboptimal quality of evidence that the extant ones provide due to the relative heterogeneity in patient populations (eg, small sample sizes, various severity grades) and testing conditions (eg, lack of standardized protocol, variable intervals from injury to assessment, diversity in technical equipment and operator skills). In this issue of Muscle & Nerve, Hearn et al enrich our knowledge on the utility of EDX testing in NBPP by evaluating the implications of median sensory NCS to digit I (thumb) and deltoid/biceps motor unit potential (MUP) recruitment in upper brachial plexus injuries. They do so by retrospectively reviewing the preoperative EDX recordings obtained antidromically without sedation in 38 infants (including 4 preterm ones) with severe, upper brachial plexus, perinatal injuries who underwent surgical intervention in a single, tertiary referral center. Most patients were tested at 3 months of age, including median sensory NCS to the thumb of the affected limb (using the contralateral thumb for comparison in the majority, with a ≥50% amplitude difference as the criterion of abnormality) and needle EMG to the deltoid and/or biceps muscles (focusing on MUP recruitment rather than abnormal spontaneous muscle activity or MUP remodeling). The primary objectives of their study were to demonstrate feasibility of this technique in infancy, establish reference values and identify its diagnostic utility in upper brachial plexus injuries at this age group. A secondary analysis was performed to evaluate whether the ability to record MUPs in the biceps and/or deltoid muscles of the affected limbs can identify C6 nerve root avulsions. The authors concluded that median to digit 1 sensory NCS can be reliably performed Abbreviations: CMAPs, compound muscle action potentials; CTM, computed tomography myelography; EDX, electrodiagnostic; EMG, electromyography; MRI, magnetic resonance imaging; MEPs, motor evoked potentials; NAPs, nerve action potentials; NBPP, neonatal brachial plexus palsy; NCS, nerve conduction studies; SSEPs, somatosensory evoked potentials; US, ultrasound. Received: 16 March 2022 Revised: 21 March 2022 Accepted: 22 March 2022