This is the Electrodiagnosis and Pediatrics Focused Review module by Jill Mylan and Erin Conley. The purpose of this module is to review principles in electrodiagnostic medicine pertinent to pediatrics, describe growth effects on the values obtained in nerve conduction studies, and review electrodiagnosis in selected conditions. Pediatric electromyography and nerve conduction studies are frequently employed in the workup for many conditions afflicting children and adolescents, generally in suspected neurologic, motor, or sensory dysfunction, but also for evaluation of injury, pathologic fatigue, or neuropathic-like pain. It allows us to see pathology that can be differentiated by axon loss or demyelination, as well as neuromuscular junction and myopathic disorders. Nerve conduction studies employ a stimulus and recording electrodes to capture nerve conduction data. EMG uses a needle electrode to examine the electrical activity within the muscles, listening for insertional activity, which is activity at rest, or motor unit potentials and recruitment when the muscles are activated. Nerve conduction studies typically include the distal latency, conduction velocity, amplitude, and often F waves and H reflexes. The latency reflects the conduction down the nerve from the stimulus to the recording electrodes. For motor nerve conduction, this also includes the neuromuscular junction time. Latency is affected by distance, temperature, and health of the nerves. The peak latency is recorded for sensory nerves, and the onset latency for motor nerves. Although most EMG machines calculate the nerve conduction velocity for you, it is good to be able to do this independently. Sensory studies reflect the number of functioning axons when measuring amplitude. In motor studies, the neuromuscular junction is also included. This is also affected by temperature and the condition of nerves and muscle. The pathway for the F wave involves antidromic excitation of all stimulated motor axons traveling to the spinal cord with reactivation of a small proportion of the anterior horn cells, axon hillocks, and orthodromic action potentials of one or more motor axons traveling back to the muscle. If the F latency is longer than the F estimate, proximal slowing of conduction is suggested. H reflexes are present in both upper and lower extremities in infancy, but the upper extremity H reflexes become suppressed in most children over the course of the first year. During electrodiagnosis, the electromyographer evaluates the motor unit action potential configuration, amplitude, duration, recruitment, and the resting activity. The pertinent muscles for the suspected diagnosis should be planned in advance so it can be done quickly and without hesitation. The motor unit action potentials in infants are often shorter in duration. In young children, the amplitudes are lower and generally biphasic or triphasic. As strength of voluntary contraction increases, the number of motor unit action potentials recruited increases. While testing graded voluntary contraction is difficult in infants and children, it should still be possible to differentiate a myopathic process from a neurogenic process. Nerve conduction values in infants and young children vary from adults for a number of reasons. The nerve diameter is half of the adult diameter at birth, reaching the adult diameter between the ages of 2 and 5 years old. The nodes of Ronvier, important in myelination, reach peak internodal distance about age 5. The small size of patients can make electrode placement difficult so that accurate measurement is even more important. Nerve conduction studies values reach adult normal levels by age 3 to 5. Before age 1, nerve conduction velocities are similar in the upper and lower limbs. After age 1, the upper limb nerve conduction velocities are faster than lower limb, as is found in adults. Historically, electrodiagnosis in pediatrics was most often done for evaluation of the floppy infant. With the advances in genetics, there is concern whether this is still helpful. A decade-long study by Boston Children's Hospital found that 94% of electrodiagnostic testing was still valuable. They also found that neurogenic causes of hypotonia were more accurately diagnosed than myogenic causes. Diagnostic evaluation using electrodiagnosis is still relevant for hereditary neuropathies and or pes cavus, which can help guide the genetics assessments. It is used in the assessment of acute and chronic inflammatory demyelinating polyneuropathy, myasthenia gravis, toxic neuropathies, neonatal brachial plexopathy as a guide for surgical repair and severity, as well as trauma which may cause nerve injury. Electrodiagnosis is used in the assessment of a multitude of neuropathies in the pediatric population. A key takeaway is that ulnar neuropathy is the most common mononeuropathy in children due to acute trauma. As with adults, demyelinating neuropathies show slow nerve conduction velocities and prolonged distal latencies. Lower amplitudes are consistent with axon loss neuropathies. Electrodiagnosis may be requested in the assessment of congenital myopathy in infants with generalized hypotonia. Chief goal is to distinguish between neurogenic and myopathic etiologies. Electrodiagnostic is rarely needed in assessment of dystrophies as molecular genetic testing is the primary diagnostic tool. Electrodiagnosis does have usefulness in the assessment of polymyositis, dermatomyositis, metabolic myopathies, and myotonias. With the current eradication of polio from all countries with the exception of Pakistan and Afghanistan, spinal muscular atrophy remains as the most common anterior horn cell disease in infants and children. Nigeria most recently was found to be clear of wild poliovirus. Spinal muscular atrophy is an autosomal recessive genetic disorder. It can be very severe in infancy with severe floppy infant syndrome. Genetic testing is available and electrodiagnosis is used as supplementation. Spontaneous activity is best seen in gastrocnemius and triceps with recruitment and motor unit configuration best seen in anterior tibialis and biceps. Neuromuscular junction disorders found in infants and children include infantile botulism, transient neonatal myasthenia gravis, toxins such as magnesium and organophosphates. Assessment of neuromuscular junction disorders is done by repetitive nerve stimulation. Electrodiagnosis of neonatal birth brachial plexus injuries is useful to determine the location, extent, and severity of the injury. This should actually be done fairly early, around three to four weeks after injury, to help plan conservative versus potentially surgical repair. Somatosensory evoked potentials can be used to help determine sensory levels in the very young or comatose patients. In summary, electrodiagnosis remains a valuable tool in the evaluation of suspected neuromuscular conditions of infants and children. It is useful in the assessment of generalized infantile hypotonia with findings better for neurogenic than myogenic etiologies. Age and size of the patient affects nerve conduction study values with adult nerve conduction values reached by age 5 in most cases. Ulnar neuropathy is the most common mononeuropathy in children. Other selected conditions were reviewed.

Electrodiagnosis

Pediatrics

Electromyography

Nerve conduction studies

Pediatric neurology