As in adults, the use of electrodiagnostic studies in pediatric patients provides an extension of the neurologic examination facilitating evaluation of the physiology of the neuromuscular system. However, pediatric electrodiagnostic studies require further consideration by the practitioner due to variations in pathology, normative values, technical factors, and diagnostic approaches relative to adult assessments. For example, diagnoses such as focal entrapment neuropathies that are commonly seen in adults are not encountered as frequently in children. Additionally, many neuromuscular disorders including congenital myopathies present in childhood require consideration by the electrodiagnostician. Due do physiologic and anatomic differences of nerves in infants and children compared with adults, skilled electromyographic (EMG) techniques are essential for accurate interpretation and diagnosis. Incorporating approaches to improve cooperation of pediatric patients helps to build the foundation for consistently obtaining complete and well-tolerated studies. This chapter explores various aspects of pediatric electromyography in order to provide readers with useful information that can be implemented to optimize their practices.
While the pathophysiology of nerves in children is similar to that of adults, there are some important differences that must be considered when performing pediatric studies. Starting from conception, nerves undergo a maturation process during which the nodes of Ranvier achieve their peak internodal distances around 5 years of age. Nerve myelination begins between the tenth and fifteenth weeks of gestation and is typically completed by the child's fifth birthday. Pediatric patients have a smaller nerve diameter relative to adult nerves.1 Given the short stature of pediatric patients, the nerve lengths of children are frequently shorter than comparable segments in postpubescent individuals. These structural differences, along with shorter nerve lengths, may affect the nerve conduction study (NCS) values obtained in pediatric studies. The nerve conduction velocity becomes a very sensitive parameter in children due to such factors. These aspects make pediatric studies more susceptible to measurement error. Further discussion of technical considerations may be found in the section “Nerve Conduction Study.”
In relation to nerve injury, both pediatric and adult nerves can sustain demyelinating, axonal, or combination injuries. In demyelinating injuries, myelin destruction occurs first and is then followed by a process of repair. In axonal injuries, the nerve axon distal to the affected region undergoes Wallerian degeneration, and depending on the extent of axonal damage, complete regeneration may not be possible. In pediatric patients, in utero neuronal insults also should be considered. In one study of in utero alcohol exposure, the authors found decreased motor amplitudes and conduction velocities in newborns that had not improved by 1 year of life. These findings reflect sequelae of both prenatal myelin and axonal injury.2 When interpreting pediatric data, especially in newborns and infants, the risk of prenatal and/or postnatal nerve insults therefore must be considered.
The estimated time course for nerve recovery may be less in children than in adults due to shorter nerve lengths. Animal studies ...