P.214 Utility of ENMG in children with rare genetic neurogenic disorders: a case series

Abstract

As molecular genetic testing is becoming increasingly available, utility of electroneuromyography (ENMG) in pediatric patients has been called into question. We present a case series of 30 consecutive children who were diagnosed with rare genetic neurogenic disorders at the CHU Sainte-Justine between August 2016 and March 2022 (excluding CMT1A). We describe phenotypes, genotypes as well as NCS and EMG findings, describing their clinical significance and diagnostic utility in this group. 26/30 subjects underwent ENMG. Median age at first EMG was 5.4 years (0.44-18.35). Mean number of sensory nerve action potential (SNAP) examinations per study was 2.4, 2.5 for compound motor action potential (CMAP) and 1.3 for number of muscles examined by EMG. One child required sedation for the test and the only complication was lipothymia in another. 6/30 children had known familial molecular diagnosis at time of ENMG. After ENMG, median number of genetic tests before reaching the final diagnosis was 2 (1-5). 12 subjects were diagnosed with a CMT subtype, 8 with 5q SMA and 5 with non-5q SMA. Other diagnoses included 1 subject with metachromatic leukodystrophy, 1 with Friedreich ataxia and 2 with posterior column ataxia with retinitis pigmentosa. Median delay between first symptoms and diagnosis was 2.1 years. Genetic diagnoses directly led to treatment in 8 patients with 5q SMA. Excluding subjects with known familial or personal mutations, electrophysiologic findings allowed to confirm and localize a peripheral nervous system (PNS) disorder and were concordant with the final molecular diagnosis in 19/21 subjects who underwent ENMG. ENMG helped direct genetic testing in 18/26 patients and allowed more comprehensive phenotyping in 5. This case series demonstrates the usefulness and feasibility of ENMG in the work-up of pediatric genetic neurogenic disorders.