Patch Versus Needle Electromyography For Evaluation of Urinary Sphincter Function - A Direct Comparison
Hsin-Hsiao Scott Wang, MD, MPH, MBAn, Ted Lee, MD, MSc, Hatim Thaker, MD, Anudeep Mukkamala, MD, Caitlynn Feng, BS, Stuart Bauer, MD, Carlos Estrada, MD, MBA.
Boston Children's Hospital, Boston, MA, USA.
Introduction: Needle electromyography (EMG) is the gold standard for studying striated muscle innervation. However, its use for assessing external urinary sphincter function has been limited. Instead, surface patch electrode EMG is routinely used to determine pelvic floor function and hence detrusor-sphincter coordination. However, the accuracy of patch EMG compared to needle EMG is not known. We sought to compare patch and needle EMG signals simultaneously and characterize their differences in children.
Methods: We prospectively enrolled children scheduled for urodynamic study (UDS) during March-April 2023 at our institution. Enrolled patients underwent simultaneous patch EMG and concentric needle EMG evaluation. Patient covariates included age at UDS, gender, and urologic diagnosis. Primary outcomes for both patch and needle EMG were defined as the ability to characterize sphincter muscle motor unit potentials (normal potentials, complex repetitive discharges, fibrillations), sacral reflexes (Valsalva, Crede, bulbocavernosus, anocutaneous reflex), and detrusor sphincter coordination (synergy versus dyssynergy) during bladder filling and emptying. All EMG studies were reviewed independently by two urologists.
Results: Thirty-one patients were enrolled. Seven were excluded due to inability to attach surface patch EMG electrodes. Of the final 24 patients, 67% were female with the median age at 8.5 (IQR 2.4-13.8) years. Their underlying conditions included spina bifida (11), tethered cord (8), spinal cord injury (1), sacral agenesis (1), and voiding dysfunction of unclear etiology (3).
The evaluation of detrusor-sphincter coordination is summarized in Table 1. 9 patients did not void and therefore could not be evaluated. Among the 15 patients who voided, 10 patients had silencing of sphincter EMG motor unit potentials during voiding on needle EMG and therefore were synergic. In these same 10 patients, only 1 patch EMG study demonstrated synergy, 2 showed significant artifact that made it impossible to assess, and the remaining 7 showed dyssynergy (active increase in activity during voiding, Figure 1). The sensitivity for patch EMG to detect dyssynergy was 40% and specificity 10%.
Complex repetitive discharges (a sign of acute denervation) were observed on needle EMG in 2 but were not discernable on patch EMG. No patient had fibrillation potentials (a sign of acute denervation) on needle EMG. Sacral reflexes were discernable in 100% of needle EMG tracings but only 50% of the patients exhibited similar responses in patch EMG with lower amplitudes.
Conclusions: Compared with needle EMG, patch EMG was found to have highly inconsistent results. An inaccurate diagnosis of detrusor sphincter dyssynergy may lead to unnecessary or inappropriate management. For patients in whom sphincter function evaluation is beneficial, needle EMG should be strongly considered to provide accurate and complete data, especially when information about innervation to the external urethral sphincter is critical.
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