ADVANTAGES AND PITFALLS OF ELECTRODIAGNOSTIC TESTS IN THE ASSESSMENT OF CHILDREN WITH NEUROMUSCULAR DISORDERS AND CORRELATION WITH THE MYOPATHOLOGICAL STUDY

Introduction: Neurophysiological investigations are an essential part in the diagnostic algorithm of neuromuscular pathologies, especially for patients with more heterogeneous phenotypes for which recognizing the early and subtle changes is essential. In children these techniques are often avoided because they are considered invasive, difficult to perform due to poor compliance, and difficult to interpret. Normative data of nerve conduction studies (NCSs) and electromyography (EMG) for the study of neuromuscular diseases in paediatric age are currently lacking in the literature. This greatly limits their clinical and research use. The diagnosis ultimately requires a muscle biopsy, regardless of the electrodiagnostic study results. Muscle biopsy has historically been considered to be the gold standard in the diagnosis of muscle disease. However, muscle biopsy is an expensive, invasive, time-consuming, and resource-dependent procedure. Aims and Methods: The first aim of this study was to collect and define a reference range of normal sensory and motor nerve conduction values of the upper and lower limbs during the maturation phases from newborn to three years of age and to collect and define a reference range of normal EMG values the maturation phases from newborn to six years of age, using quantitative EMG in the paediatric field to obtain the normative values of the main parameters, by means of the e-norms method. The secondary aim was to describe the diagnostic accuracy of electrodiagnostic tests (NCS and EMG) and muscle biopsy in children with suspected neuromuscular disorders. The study aimed to compare the sensitivity, specificity, positive and negative predictive value of the two tests and demonstrate in a systematic way if correlations between electrophysiological parameters and histopathologic findings in the same paediatric population exist; to performed the correlation between EMG and muscle biopsy variables Fisher’s exact test was used. Results: E-norms were calculated for Sural, Medial Plantar and Median sensory studies, and for Median, Peroneal and posterior Tibial motor studies. Regarding EMG, a reference range of motor unit potentials (MUPs) amplitude, MUPs duration, Turns/sec and Turn/Amplitude (TAA) was calculated. Regarding the diagnostic value of neurophysiological test and muscle biopsy, EMG was found to be particularly sensitive (100%) and specific (81%) in recognising neurogenic disorders, while muscle biopsy had a modest sensitivity (62%) and high specificity (89%). In our sample, the sensitivity of EMG in detecting myopathies is very low (26%), while the specificity remained high (95%); muscle biopsy had a very high diagnostic yield in myopathic disorders, with discrete sensitivity (65%), but very high specificity (100%). Some interesting correlations between EMG and histopathological results have been found. Increased amplitude of MUPs is correlated with the presence of fibre type grouping, while reduced amplitude is correlated with the presence of fibrosis and necrosis. Long duration of MUAPs is correlated with necrosis. Increased phases are sensitive for grouping and necrosis. A statistically significant correlation was also noted between a reduction of T/A at EMG and the presence of necrosis on muscle biopsy. Conclusions: Focused neurophysiological tests and muscle biopsy remain in children of all ages an indispensable diagnostic tool to guide clinicians in their decision-making and help in prompt diagnosis. The possibility of obtaining normal values from the neurophysiologist's laboratory adds their clinical and research use. Regarding EMG investigations, this study reports the first normative values for quantitative EMG in the international neurophysiological field, specifically the Turn/sec and TAA paediatric values. By demonstrating correlation between EMG findings and muscle biopsy results in a paediatric sample, this work could serve as a pilot study for future studies to better understand the muscle biopsy-neurophysiological tests correlation in specific neuromuscular disorders affecting developmental age.