EMG Considerations in the Pediatric Patient

Gloria M. Galloway, MD, FAAN

FEAR AND DISCOMFORT

Performing electrodiagnostic procedures in pediatric patients can be challenging in part because the test can be uncomfortable but more importantly because the young child will be fearful of a new procedure and not understand what will be involved. Therefore having a realistic expectation of the patient’s (and parents’) level of cooperation is necessary. In some cases, electrodiagnostic evaluations in young children and infants may be limited due to limits on patient and parent tolerance. This is particularly true in very small children and infants.

MYOPATHIC DISORDERS

One situation in particular where electrodiagnostic testing can be difficult in a small child is in the workup of suspected myopathic disorders. In these studies, much patience in obtaining motor unit analysis is needed and can be more time-consuming than a young child (or parent) can tolerate. Several studies have evaluated the role and accuracy of an electromyogram (EMG) in the diagnosis of neuromuscular disorders in children and infants. EMG has also been compared to muscle biopsy in diagnostic specificity and sensitivity of the procedures. In a majority of these studies, the accuracy of diagnosis with EMG improves in older children compared to the very young, likely mainly due to the level of tolerance of the procedure. However, EMG remains most difficult in the case of myopathic disorders in infants and very young children (1).

Ghosh and colleagues evaluated over a several-year period the diagnostic sensitivity of EMG in pediatric patients between the ages of 6 months and 18 years who underwent both EMG and muscle biopsy evaluations in cases of suspected myopathic disorders. A myopathic EMG was defined as having motor potentials that are of short duration, low amplitude, and polyphasic along with rapid recruitment. In their population, the most common diagnoses in decreasing order of frequency were congenital myopathy, metabolic myopathy, muscular dystrophy, genetically confirmed myopathy, myopathy undefined, and inflammatory myopathy. The authors concluded from their experience and comparisons that pediatric electromyography was 91% sensitive and 67% specific in diagnosing myopathic disorders with metabolic myopathies most commonly missed using EMG in this patient population (2).

THE ROLE OF GENETIC TESTING

One would expect the use of genetic testing in the diagnosis of muscular disorders to correspond to a decrease in the use of EMG in the pediatric population. However, this may not always be the case. In a study at Boston Children’s Hospital (3) over a 10-year period from 2001 to 2011, a total of 2,100 studies were evaluated. In their review, the volume of studies actually increased from approximately 160 to 250 studies/year, with a trend toward studying older children. Referral for EMG was predominately from neurologists, including neuromuscular specialists. One reason for this is that with the possibility of genetic diagnosis, an EMG may be considered more useful in its ability to allow screening when these disorders are suspected. This screening may mitigate the expense of genetic testing to those disorders in which there is greater likelihood of a valid genetic diagnosis, a change to a health care plan of action, or a family’s decision to have additional children. Also important in this process is that in many cases, genetic testing may not be reimbursed by a patient’s health insurance plan. In this way, genetic testing along with EMG used to screen for myopathy in these patients may allow additional options available for the patient and family. In this Boston Children’s Hospital study, polyneuropathies and mononeuropathies were the most common reason for referral. They found that 57% of the studies were normal, but EMG was able to provide diagnostically useful information in 94% of the cases.

EMG IN CLINICAL TRIALS

Using EMG parameters to follow a patient’s response to treatment or course of disease is being used increasingly in clinical trials. In pediatric multicenter clinical trials in spinal muscular atrophy (SMA), using the maximum ulnar compound muscle action potential (CMAP) amplitude and area has been shown to provide a valid and reliable outcome measure that significantly correlates with clinical motor function. CMAP amplitude and area therefore have potential value as measures to evaluate and follow disease status in the trials of pediatric patients (4).

USE OF SEDATION

Adding to the challenge of performing these procedures in young children and infants is the fact that frequent pain assessments and the need for adequate pain control are often stipulated by the facility or institution and can be the subject of health performance survey data as part of the patient satisfaction score known as HCHAPS (Hospital Consumer Assessment of Healthcare Providers and Systems) (5). These surveys are increasingly used to judge the performance of a facility and are accessible to the public for review and scrutiny. Therefore, an incentive exists for each health care facility to merit a high score on survey data of patient satisfaction. Health care providers are encouraged to provide a “pain-free environment” and this may be at odds with the ability to perform complete and adequate electrodiagnostic evaluations in young children. The use of sedation can interfere with the complete evaluation of interference patterns, and depending on the level of sedation, motor unit analysis can be significantly impacted. More so than in studies in adult patients, preparation of the environment along with an honest discussion about expectations with the parents and child is needed in order to accomplish an appropriate study. Importantly it should be communicated to the parent and child that some level of discomfort should be expected. Since voluntary movements can interfere with the ability to adequately evaluate spontaneous resting activity, successful evaluation can only be obtained in a calm child. The use of conscious sedation during electrodiagnostic procedures in infants and children requires additional staffing to meet most regulatory requirements. This includes a provider skilled (and certified) in sedation procedures to be present for monitoring oxygen and vitals throughout the procedure and for a period thereafter. Additionally this provider needs to not be the provider performing the electrodiagnostic procedure. Although the use of conscious sedation is possible while obtaining nerve conduction studies, the child would need to be awake for the EMG component of the study. In general, the use of sedation significantly prolongs the total test time. Once the sedation wears off, it can be frightening for a young child to awaken and find an uncomfortable procedure about to begin, making cooperation often even less likely. In these cases, a realistic expectation would be that only limited information will be possible from the study. Motor unit analysis can be possible only with patience, a knowledgeable sedating team, informed parents, and a cooperative child (6).

DISEASE ETIOLOGIES

In some instances, neuromuscular disorders compare similarly in children and adults with little variation. One example of this is in the case of critical illness myopathy or critical illness polyneuropathy. Critical illness polyneuropathy and critical illness myopathy are associated with generalized weakness along with respiratory compromise and difficulty in weaning from mechanical ventilation. This has been reported in approximately 30% of the patients hospitalized for more than 3 days with a life-threatening illness (7). Since clinically and electrophysiologically polyneuropathic and myopathic features can be seen in the same patient, the disorder is often referred to as critical illness polyneuropathy and myopathy (CIPNM) (8).

In contrast, in many cases, the underlying etiological factors underlying a disorder vary significantly in infants and children compared to the adult population. An example of this is seen prominently with mononeuropathies. Mononeuropathies represent one of the most common sources of referrals for electrodiagnostic evaluation in the adult population but are less common in pediatrics. In children when carpal tunnel syndrome is seen in association with trigger finger and joint stiffness, a suspicion for mucopolysaccharidoses should be raised. Mucopolysaccharidoses are associated with joint stiffness and swelling and can also be associated with contractures (9).

Additionally, the more common sites for mononeuropathies are different in young children. Carpal tunnel and ulnar neuropathy make up the majority of adult mononeuropathy referrals in the outpatient setting with early presentation of paresthesias and progression to motor weakness. In contrast, in pediatric patients, sciatic mononeuropathy may account for 25% of all such cases (10). In the majority of these cases, the presentation is that of motor weakness. The underlying etiology of sciatic mononeuropathy may include trauma and injury from surgical causes and less commonly vascular or neoplastic processes. Other etiologies include prolonged extrinsic compression and immobilization. As in adults, the prognosis for recovery depends on the electrodiagnostic findings and degree of severity. Idiopathic etiologies may result from orthopedic surgeries or after prolonged compression with a cast. In most of these cases, peroneal followed by tibial nerve–innervated muscles are involved. Use of intraoperative EMG monitoring during surgical procedures in which the sciatic nerve is at risk of injury may reduce the risk of nerve-related injury. The severity can be evaluated both clinically and electrodiagnostically. The presence of reinnervation is a good prognostic sign as is the presence of normal-amplitude nerve action potentials (NAPS). Other rare causes of sciatic mononeuropathy include intraneural perineurioma of the sciatic nerve, which is treatable and has an indolent course. Electrodiagnosis and imaging with MRI in the appropriate clinical setting of intraneural perineurioma provide the correct diagnosis (11). Vascular etiologies are uncommonly seen as the cause of sciatic neuropathies in children but when present, may be due to vasculitis, embolization, or infectious etiologies (12).

Carpal tunnel syndrome or median neuropathy at the wrist is the most common mononeuropathy of adulthood but uncommon in children. It is characterized by paresthesias in the hand overlying the first three digits and can be associated with hand weakness and wrist pain. Electrophysiological findings include slowing of nerve conduction velocity at the palm-to-wrist segment along with latency prolongation at the wrist. In adults most often, this disorder is due to repetitive use of the hands and can be seen commonly in those with diabetes, other endocrine conditions, connective tissue disorders, and in pregnancy. In children however, in mucopolysaccharidoses and mucolipidoses, trauma to the median nerve, malformations of the wrist, brachial plexopathy, obesity, and inherited susceptibility to pressure palsies (PMP 22 gene deletion) are all possible as etiologies. In addition, family history of median neuropathy at the wrist is commonly seen (13).

Another example of different underlying etiologies for the same clinical condition in children compared to adults is in the case of acute axonal peripheral polyneuropathy. Toxic etiologies account for more than 50% of cases of acute axonal peripheral polyneuropathies in children, a larger percentage than in adults. In the case of purely sensory peripheral neuropathy, diabetes is responsible for most cases in children, whereas in adults, a purely sensory peripheral neuropathy necessitates a thorough diagnostic investigation for other etiologies including paraneoplastic disorders. Autoantibodies to gangliosides GM1, GM1b, GD1a, GD1a, or galNac-GD1a may be present is some children with acute motor axonal neuropathy and their clinical presentations are similar to those seen in adult patients (14). When these ganglioside markers are present in children, recovery from the neuropathy may be prolonged. In contrast to axonal neuropathies, pediatric cases of childhood multifocal acquired demyelinating sensory and motor neuropathy have been reported with and without conduction block on electrophysiological studies. These cases may respond to intravenous immunoglobulin (IVIG) therapy with more favorable long-term outcomes.

CLINICAL COURSE, ELECTRODIAGNOSIS, AND OUTCOME

Another consideration when interpreting EMG findings in children is that the same clinical condition may have very different presentations, electrodiagnostic findings, and outcomes. An example of this is with pediatric thoracic outlet syndrome. In these cases, vascular compromise is much more common than in adults. There is significant clinical and electrodiagnostic involvement and surgical rib resection is likely to result. In addition, a significant number of these cases are due to hypercoagulable disorders (15). Another example of the variability seen in children is in children with Guillain-Barré syndrome, the presentation may be that of leg pain and gait disturbance, but prognosis for complete recovery with IVIG is good (16). In the newborn and infant age group, often the presentation is that of muscle weakness or of a floppy infant. In this scenario, the differential diagnosis is wide and includes spinal muscular atrophy type 1, poliomyelitis (not so often in developed nations), as well as hereditary myopathies, infantile botulism, and Guillain-Barré syndrome.

Another potentially devastating disorder with a different clinical course in children is that of chronic inflammatory demyelinating polyneuropathy (CIDP). CIDP is characterized by clinical weakness, increased cerebrospinal fluid protein, and electrophysiological evidence of demyelination with varying degrees of axonal involvement. It is much less common in children than in adults, and in general, children tend to have a more severe and rapidly progressive course. Children, however, often show a more rapid improvement after therapy and ultimately have a more favorable overall outcome. Favorable response to IVIG or plasmapheresis is typical. However, in those patients who are not responsive to IVIG or plasmapheresis, a more prolonged course of recovery is found and variable responsiveness to other immune modulating treatments is also seen (17).

Neuromuscular junction disorders in children generally have a more severe clinical presentation than that seen in adults. Clinical presentations include floppy infant and apnea episodes leading to a broad differential diagnosis and can delay diagnosis and treatment (18). The genetic abnormalities involved in these disorders are numerous, so genetic screening without EMG confirmation is impractical. Neuromuscular junction disorders in children include the congenital myasthenic syndromes and autoimmune myasthenia gravis, which are uncommon. Stimulated single-fiber electromyography (stim SFEMG) of a proximal muscle such as the orbicularis oculi has a high sensitivity and specificity for diagnosis and although technically more difficult to do, at least in older children it may be very well tolerated.

Understandably, EMG in pediatric patients can be more challenging than in adults due to limitations in tolerance. Having an understanding of the limitations of the study in each case and maximizing the ability to obtain as much information as possible can be realized with informed parents and a sedating team when sedation is needed or required. Engaging both the parents and the sedating team in furthering the cooperation of the child is optimum and a key to the successful completion of EMG studies in these patients.

REFERENCES

1. Rabie M, Jossiphov J, Nevo Y. Electromyography (EMG) accuracy compared to muscle biopsy in childhood. J Child Neurol. 2007;22(7):803–808.

2. Ghosh PS, Sorensen EJ. Diagnostic yield of electromyography in children with myopathic disorders. Pediatr Neurol. 2014;51(2):215–221.

3. Karakis I, Liew W, Darras BT, et al. Referral and diagnostic trends in pediatric electromyography in the molecular era. Muscle Nerve. 2014;50(2):244–249.

4. Lewelt A, Krosschell KJ, Scott C, et al. Compound muscle action potential and motor function in children with spinal muscular atrophy. Muscle Nerve. 2010;42(5):703–708.

5. http://www.hcahpsonline.org. Centers for Medicare & Medicaid Services. Baltimore, MD 2015

6. Galloway G. The preoperative assessment. In: Galloway G, Nuwer M, Lopez J, Zamel K. eds. Intraoperative Neurophysiogic monitoring. New York, NY: Cambridge University Press;2010:10–18.

7. Jones, HR, Darras, BT. Acute care pediatric electromyography. Muscle Nerve Suppl. 2000;9:S53–S62.

8. Williams S, Horrocks A, Ouvrier RA, et al. Critical illness polyneuropathy and myopathy in pediatric intensive care: A review. Pediatr Crit Care Med. 2007;8(1):18–22.

9. Cimaz R, La Torre F. Mucopolysaccharidoses. Curr Rheumatol Rep. 2014;16:389.

10. Srinivasan J, Ryan MM., Escolar DM, et al. Pediatric sciatic neuropathies: a 30 year prospective study. Neurology. 2011;76:976–980.

11. Ostergaard JR, Smith T, Stausbol-Gron B. Intraneural perineurioma of the sciatic nerve in early childhood. Pediatr Neurol. 2009;41(1):68–70.

12. Srinivasan J, Escolar D, Ryan M. et al. pediatric sciatic neuropathies due to unusal vascular casuses. J Child Neurol. 2008;23(7):738–741.

13. Davis L, Vedanarayanan V. Carpal tunnel syndrome in children. Pediatr Neurol. 2014;50(1):57–59.

14. Nishimoto Y, Susuki K, Yuki N. Serologic marker of acute motor axonal neuropathy in childhood. Pediatr Neurol. 2008;39(1):67–70.

15. Arthur LG, Teich S, Hogan M. et al Pediatric thoracic outlet syndrome: a disorder with serious vascular complications. J Pediatr Surg. 2008;43(6):1089–1094.

16. Devos D, Magot A, Perrier-Boeswillwald J, et al. GB syndrome during childhood: particular clinical and electrophysiological features. Muscle Nerve. 2013;48(2):247–251.

17. Riekhoff AG, Jadoul C, Mercelis R, et al. Childhood chronic inflammatory demyelinating polyneuro-radiculopathy—three cases and a review of the literature. Eur J Paediatr Neurol. 2012;16(4):315–31.

18. Wakamotor H, Chisaka A, Inoue N, Nakano N. Childhood multifocal acquired demyelinating sensory and motor neuropathy. Muscle Nerve. 2008;37(6):790–795.

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