Approach to Pediatric Electromyography

SECTION VII • Electromyography in Special Clinical Settings

Approach to Pediatric Electromyography

In conjunction with the clinical examination, electrodiagnostic (EDX) studies frequently play a key role in the evaluation of neuromuscular disorders in infants and children. Indeed, there are a large number of neuromuscular disorders that present in the pediatric age group. In many of these cases, EDX studies are used to help guide further evaluation (e.g., muscle biopsy, genetic testing); less commonly, they can make a definitive diagnosis. A complete discussion of pediatric neuromuscular disorders and electrodiagnosis is beyond the scope and purpose of this chapter (see Suggested Readings). Although the fundamental principles of EDX studies are the same for pediatric and adult age groups, there are significant differences that the electromyographer needs to keep in mind when studying infants and children. These differences include both physiologic and non-physiologic factors that may vary considerably between age groups.

NEUROMUSCULAR DIAGNOSES ARE DIFFERENT IN CHILDREN THAN IN ADULTS The most common referral diagnoses to the typical electromyography (EMG) laboratory include radiculopathy, polyneuropathy, and carpal tunnel syndrome. However, adults are more commonly studied in the EMG laboratory, so this group of diagnoses reflects neuromuscular conditions seen in the adult age group. In contrast, the neuromuscular disorders seen in children often are different. For example, entrapment neuropathies are very common in adults but are extremely rare in children. Likewise, radiculopathy, probably the most common of all EMG referral diagnoses, is virtually unheard of in children, except in cases of trauma. Although peripheral neuropathies occur in children, they are most often genetic, whereas most peripheral neuropathies in adults referred to the EMG laboratory are acquired disorders, usually toxic, metabolic, inflammatory, or associated with other coexistent medical illnesses. Unlike adults, the more common diagnoses in children referred to the EMG laboratory are inherited disorders of the motor unit, including the anterior horn cell (e.g., spinal muscular atrophy), peripheral nerve (e.g., Charcot–Marie–Tooth), or muscle (e.g., muscular dystrophy). ©2013 Elsevier Inc DOI: 10.1016/B978-1-4557-2672-1.00038-6

38 

Children with neuromuscular disorders often present clinically as a delay in motor milestones. In many cases, it may not be clear from the symptoms and signs whether the etiology is central or peripheral. One of the best examples of this predicament is that of the floppy infant, in whom the differential diagnosis includes the entire length of the neuraxis, from brain to muscle. In this regard, EDX studies often are helpful in differentiating peripheral from central etiologies and, accordingly, guiding the subsequent evaluation in a useful and logical direction.

MATURATION ISSUES When studying children, it is essential to appreciate what is normal for what age. This is especially important when interpreting conduction velocities and differentiating a normal conduction velocity from axonal loss or demyelination. Most adult electromyographers who study adults are well versed in the EDX criteria for demyelination: • Conduction velocities less than 75% the lower limit of normal • Distal latencies and late responses greater than 130% the upper limit of normal • Conduction block, which signifies not only demyelination but acquired demyelination However, infants and young children often have slowed conduction velocities that would be considered in the “demyelinating range” for adults. In most cases, this is not because infants and young children have demyelinated nerves; rather, they have nerves that have yet to be myelinated in the first place. The process of myelination is age dependent, beginning in utero, with nerve conduction velocities in full-term infants approximately half that of adult normal values. Accordingly, nerve conduction veloci­ ties of 25 to 30 m/s are normal at birth. Conduction velocity rapidly increases after birth, reaching approximately 75% of adult normal values by age 1 year, and the adult range by age 3 to 5 years, when myelination is complete. Accordingly, when a child is studied in the EMG laboratory, it is essential that age-based normal control values are used (Tables 38–1 and 38–2). One interesting aspect of myelin maturation is often observed during the nerve conduction studies. Many are familiar with the fact that different white matter tracts in

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SECTION VII Electromyography in Special Clinical Settings

Table 38–1.  Pediatric Motor Conduction Studies by Age Median Nerve

Peroneal Nerve

DML (ms)

CV (m/s)

F (ms)

AMP (mV)

DML (ms)

CV (m/s)

F (ms)

AMP (mV)

7 days–l month

2.23 (0.29)*

25.43 (3.84)

16.12 (1.5)

3.00 (0.31)

2.43 (0.48)

22.43 (1.22)

22.07 (1.46)

3.06 (1.26)

1–6 months

2.21 (0.34)

34.35 (6.61)

16.89 (1.65)

7.37 (3.24)

2.25 (0.48)

35.18 (3.96)

23.11 (1.89)

5.23 (2.37)

6–12 months

2.13 (0.19)

43.57 (4.78)

17.31 (1.77)

7.67 (4.45)

2.31 (0.62)

43.55 (3.77)

25.86 (1.35)

5.41 (2.01)

1–2 years

2.04 (0.18)

48.23 (4.58)

17.44 (1.29)

8.90 (3.61)

2.29 (0.43)

51.42 (3.02)

25.98 (1.95)

5.80 (2.48)

2–4 years

2.18 (0.43)

53.59 (5.29)

17.91 (1.11)

9.55 (4.34)

2.62 (0.75)

55.73 (4.45)

29.52 (2.15)

6.10 (2.99)

4–6 years

2.27 (0.45)

56.26 (4.61)

19.44 (1.51)

10.37 (3.66)

3.01 (0.43)

56.14 (4.96)

29.98 (2.68)

7.10 (4.76)

6–14 years

2.73 (0.44)

57.32 (3.35)

23.23 (2.57)

12.37 (4.79)

3.25 (0.51)

57.05 (4.54)

34.27 (4.29)

8.15 (4.19)

Age

*Mean (SD). DML = distal motor latency; CV = conduction velocity; F = F-latency; AMP = amplitude. From Parano, E., Uncini, A., DeVivo, D.C., Lovelace, R.E., 1993. Electrophysiologic correlates of peripheral nervous system maturation in infancy and childhood. J Child Neurol 8, 336–338.

Table 38–2.  Pediatric Sensory Conduction Studies by Age Median Nerve

Sural Nerve

CV (m/s)

AMP (µV)

CV (m/s)

AMP (µV)

7 days–l month

22.31 (2.16)*

6.22 (1.30)

20.26 (1.55)

9.12 (3.02)

1–6 months

35.52 (6.59)

15.86 (5.18)

34.63 (5.43)

11.66 (3.57)

6–12 months

40.31 (5.23)

16.00 (5.18)

38.18 (5.00)

15.10 (8.22)

1–2 years

46.93 (5.03)

24.00 (7.36)

49.73 (5.53)

15.41 (9.98)

2–4 years

49.51 (3.34)

24.28 (5.49)

52.63 (2.96)

23.27 (6.84)

4–6 years

51.71 (5.16)

25.12 (5.22)

53.83 (4.34)

22.66 (5.42)

6–14 years

53.84 (3.26)

26.72 (9.43)

53.85 (4.19)

26.75 (6.59)

Age

*Mean (SD); CV = conduction velocity; AMP = amplitude. From Parano, E., Uncini, A., DeVivo, D.C., Lovelace, R.E., 1993. Electrophysiologic correlates of peripheral nervous system maturation in infancy and childhood. J Child Neurol 8, 336–338.

the central nervous system myelinate at different times. Indeed, one can often use the pattern of myelination on a brain magnetic resonance imaging (MRI) scan to correctly predict the age of a young child. Similarly, different fibers in the peripheral nervous system myelinate at different times as well. In the EMG laboratory, this often manifests as a bifid morphology (i.e., two separate peaks) on sensory nerve action potentials (SNAPs) in infants and children (Figure 38–1). This bifid morphology is due to some fibers having already been fully myelinated (the first peak), whereas others have not and trail behind (i.e., the second peak). It is not unusual to see bifid SNAPs between the ages of 3 months and 4 to 6 years. These bifid SNAPs are a completely normal finding. Eventually, as the fibers in the second peak fully myelinate, the second peak moves to the left and merges with the first peak. This forms a larger sensory response, as is typically seen in adults.

10 µV 2 ms

FIGURE 38–1  Sural sensory nerve action potential in a young child. Note the bifid morphology. These bifid sensory responses are a completely normal finding between the ages of 3 months through 4 to 6 years. They occur as different populations of fibers myelinate at different times. Eventually, the group of fibers in the second peak will fully myelinate. The second peak will move to the left and merge with the first peak to form a larger sensory response.

Chapter 38 • Approach to Pediatric Electromyography

As with adults, the F response can be easily studied in children. Although the F response often is thought of as evaluating the proximal nerve segments, it assesses the entire length of the nerve, from the stimulation point to the spinal cord and back, and then past the stimulation point to the muscle. Thus, the F response latency depends not only on the conduction velocity and distal latency but also on the length of the limb. Because infants and children have slower conduction velocities than adults, one would expect the F responses to be very long. However, counterbalancing this is the very short limb length of a child compared to an adult. Thus, there are two opposing influences on the F response in children: limb length and conduction velocity. In infants and young children, the influence of the limb length is more overriding, resulting in F-wave latencies that are much shorter in children than adults (typically in the range of 16–19 ms in the upper extremities). Thus, whenever an F response is performed on a child, it is essential to compare it to normal control values for the child’s age or height. The most important maturation issue for the needle EMG portion of the examination is the size of the motor unit. It is no surprise that the physical size of a motor unit of a newborn is much smaller than that of an adult. Transverse motor unit territory increases greatly with age, doubling from birth to adulthood, mostly because of the increase in individual muscle fiber size. Thus, normal motor unit action potentials (MUAPs) in infants typically are very small, representing the physical size of the motor unit. Indeed, in infants, it often is difficult to differentiate normal MUAPs from myopathic ones. This once again underscores that when one interprets EDX findings in children, including MUAPs, it is essential to use age-based normal control values (Table 38–3).

TECHNICAL ISSUES A large number of unique technical issues must be kept in mind when studying infants and children so that reliable and accurate data can be obtained. The first important issue is measurement of distances and its relationship to technical errors. Because a child’s limb is much smaller than an adult’s, much shorter distances are used. When short distances are used, a small error in measurement creates a much larger error in computed conduction velocities than when longer distances are used. For instance, in an adult, if the distance between the wrist and elbow is measured at 20 cm but is off by 1 cm (i.e., the true measurement is 21 cm), this results in an error of 5% when calculating a conduction velocity. However, in a newborn baby, if the measured distance is 7 cm but is off by 1 cm (i.e., the true measurement is 8 cm), the error in conduction velocity increases to 14%. Thus, one needs to be especially careful when measuring distances in children. Second, smaller electrodes often are needed in infants and young children because their limbs and muscles are so small. The typical bar electrode that has the active and reference contacts separated by 2.5 cm often is too large for most infants and small children (Figure 38–2). Standard 10 mm disc electrodes often will suffice for most ages, except for newborns in which smaller electrodes generally are needed. Likewise, the standard adult stimulator often is too large for infants and young children because of the size of the prongs and the distance between the cathode and anode. Often it is preferable to use a pediatric-sized stimulator so that the nerve of interest is more accurately stimulated (Figure 38–3). Because a child’s limbs are so much smaller than an adult’s, one needs to take great care when stimulating the

Table 38–3.  Mean Motor Unit Action Potential Duration Based on Age and Muscle Group Age of Subjects (yrs)

Arm Muscles (ms)

Leg Muscles (ms)

Deltoid

Biceps

Triceps

Thenar

ADM

Quad, BF

Gastroc

Tib Ant

Per Long

EDB

Facial

0–4

7.9–10.1

6.4–8.2

7.2–9.3

7.1–9.1

8.3–10.6

7.2–9.2

6.4–8.2

8.0–10.2

6.8–7.4

6.3–8.1

3.7–4.7

5–9

8.0–10.8

6.5–8.8

7.3–9.9

7.2–9.8

8.4–11.4

7.3–9.9

6.5–8.8

8.1–11.0

5.9–7.9

6.4–8.7

3.8–5.1

10–14

8.1–11.2

6.6–9.1

7.5–10.3 7.3–10.1 8.5–11.7 7.4–10.2

6.6–9.1

8.2–11.3

5.9–8.2

6.5–9.0

3.9–5.3

15–19

8.6–12.2

7.0–9.9

7.9–11.2 7.8–11.0 9.0–12.8 7.8–11.1

7.0–9.9

8.7–12.3

6.3–8.9

6.9–9.8

4.1–5.7

20–29

9.5–13.2 7.7–10.7 8.7–12.1 8.5–11.9 9.9–13.8 8.6–12.0 7.7–10.7 9.6–13.3

6.9–9.6

7.6–10.6 4.4–6.2

30–39

11.1–14.9 9.0–12.1 10.2–13.7 10.0–13.4 11.6–15.6 10.1–13.5 9.0–12.1 11.2–15.1 8.1–10.9 8.9–12.0 5.2–7.1

40–49

11.8–15.7 9.6–12.8 10.9–14.5 10.7–14.2 12.4–16.5 10.7–14.3 9.6–12.8 11.9–15.9 8.6–11.5 9.5–12.7 5.6–7.4

50–59

12.8–16.7 10.4–13.6 11.8–15.4 11.5–15.1 13.4–17.5 11.6–15.2 10.4–13.6 12.9–16.9 9.4–12.2 10.3–13.5 6.0–7.9

60–69

13.3–17.3 10.8–14.1 12.2–15.9 12.0–15.7 13.9–18.2 12.1–15.8 10.8–14.1 13.4–17.5 9.7–12.7 10.7–14.0 6.3–8.2

70–79

13.7–17.7 11.1–14.4 12.5–16.3 12.3–16.0 14.3–18.6 12.4–16.1 11.1–14.4 13.8–17.9 10.0–13.0 11.0–14.3 6.5–8.3

ADM, abductor digiti minimi; BF, biceps femoris; EDB, extensor digitorum brevis; Gastroc, gastrocnemius; Per long, peroneus longus; Quad, quadriceps; Tib ant, tibialis anterior. Reprinted with permission from Buchthal, F., Rosenfalck, P., 1955. Action potential parameters in different human muscles. Acta Psych Neurol Scand. Munsgaard International Publishers Ltd, Copenhagen, Denmark.

595

596

SECTION VII Electromyography in Special Clinical Settings

Bar electrode

10 mm disc electrodes

FIGURE 38–2  Pediatric electrodiagnostic studies and recording electrode size. The standard bar electrode (left) and 10 mm disc electrodes (middle) are compared to the size of an infant’s hand (right). Smaller electrodes may be needed in infants and young children because their limbs and muscles are so small. Standard 10 mm disc electrodes often will suffice for most age groups, including infants. In newborns, however, smaller electrodes are needed. Other standard electrodes, like the bar electrode, are too large for a newborn or infant’s hand.

Pediatric Standard Infant 5 year-old Adult stimulator stimulator FIGURE 38–3  Pediatric electrodiagnostic studies and stimulator size. The standard stimulator can be used for adults and most children. However, for infants and young children, it is preferable to use a pediatric-sized stimulator so that the nerve of interest is more accurately stimulated.

nerves. The stimulus intensity needs to be kept as low as possible, for patient cooperation and tolerance but also to prevent co-stimulation of nearby nerves. Co-stimulation of nerves is much more likely to occur in a young infant or child than in an adult, even at low intensities, because of the small size of the limb and the close physical proximity of the nerves to each other. During the needle EMG examination, additional technical issues arise. Because the physical size of the motor units

in children is quite small, it is often very difficult, even for the most experienced pediatric electromyographer, to differentiate normal MUAPs from myopathic MUAPs, especially in infants. Decreased recruitment and large MUAPs, as seen in neuropathic conditions, are much more straightforward and easier to appreciate in infants and children than normal or myopathic MUAPs in this population. Because individual muscle fibers are so small in infants and children, another common problem that arises in pedi­ atric electromyography is the differentiation between fibril­ lation potentials and endplate spikes. The endplate zone in infants takes up a disproportionately large territory of the muscle compared with adults. Thus, it is not uncommon to encounter endplate potentials when studying pediatric patients. Endplate spikes can easily mimic fibrillation potentials. One needs to pay especially close attention to the firing pattern (regular vs. irregular) and the initial waveform deflection (positive vs. negative) to properly differentiate fibrillation potentials from endplate spikes. Because fibrillation potentials signify active denervation, it is essential not to mistake endplate spikes for fibrillation potentials, especially in the pediatric population, where such findings may portend a particularly grave diagnosis, such as infantile spinal muscular atrophy (Werdnig–Hoffmann disease).

APPROACH TO THE CHILD AS A PATIENT Although many adults are apprehensive of EDX studies, most tolerate the study well, with minimal discomfort. In adults, explaining the test in advance and as it proceeds is often one of the most helpful ways of allaying any fears and creating good patient rapport. However, a different approach must be taken to allay fears and create rapport with an infant or child in the EMG laboratory. As most children are accompanied by their parent(s), it is often extremely helpful to have a parent in the room with the child. The parent can help comfort the child and be a valuable asset to the electromyographer. The electromyographer also might consider removing his or her white coat before entering the examination room. Speaking with the child in a supportive and comforting manner, using uncomplicated words and phrases, will help allay the child’s fears. Of course, the task is much more difficult in infants, who cannot understand the situation, and in these cases having a parent in the room is extremely valuable. There are a few helpful techniques that can be used with children to gain their cooperation. When performing the nerve conduction studies, the electromyographer can explain to the child that the stimulator will feel like a tap, buzz, or static electricity, similar to when he or she rubs the feet along the floor and then touches the refrigerator. It is best to avoid the word “shock” when explaining the nerve conduction part of the study, because the term likely has negative connotations for both children and adults. One extremely effective maneuver is to have the child hold the stimulator and stimulate the examiner’s median nerve at

Chapter 38 • Approach to Pediatric Electromyography

• Which studies are essential to help support or exclude a diagnosis

Target plasma concentration

1.00 plasma propofol concentration (ug/mL)

the wrist, using a low-stimulus current. In this way, the child can see the muscle twitch. More importantly, the child will see that the examiner is not distressed by the experience (hopefully). In children aged 5 through 10 years, we routinely have them stimulate our own nerves before we begin the study. One will find that the parent in the room often is interested in knowing what the stimulator feels like on themselves. Regarding the needle part of the test, the word “needle” should always be avoided. No one likes needles, including children. Children are very familiar with needles, usually receiving one or more vaccinations almost every time they visit their pediatrician. It is best to use the word “electrode” or “microphone” when describing the needle part of the examination. If a child is told that a very small microphone is going to be put into his or her muscle so that he or she will be able to hear the muscles along with you, the child may become very interested and engaged in the test. The most difficult age for EDX studies is between the ages of 2 and 6 years. In the infant, who cannot understand and who also cannot move around very much, EDX studies usually can be done fairly easily and quickly, with minimal discomfort to the infant, with an assistant helping immobilize the limb being studied. However, in rambunctious toddlers, EDX studies can be very difficult without their cooperation. Indeed, in this age group, conscious sedation often is very helpful. In the past, a mild sedative such as chloral hydrate was often used. This form of sedation usually was inadequate, with the child often sleeping well on the ride home after the study but not during the study. In the modern day, conscious sedation with propofol (Diprivan), under the supervision of an anesthesiologist, can be used to obtain good data with minimal discomfort to the child. Propofol is an intravenous sedative–hypnotic agent used for induction of anesthesia or for sedation. Its major advantage is that it produces hypnosis rapidly, usually within 40 seconds from the start of the injection. As with other rapidly acting intravenous anesthetic agents, the half-time of the blood– brain equilibration is approximately 1 to 3 minutes. While the child is sedated with propofol, nerve conduction studies and/or repetitive nerve stimulation studies can be performed easily. Likewise, the needle EMG study can be performed, looking for abnormal spontaneous activity, while the child is sedated. The propofol then can be turned down, and, as the child is coming out of the sedation, MUAPs can be analyzed (Figure 38–4). Pediatric electromyography nevertheless remains a challenge, even if these recommendations are followed. The more experience one has with children, the easier the testing goes. In pediatric electromyography, more than in any other situation, it is important to always follow the Willie Sutton rule: Go where the money is! One needs to carefully choose the nerves and muscles to study based on the following:

0.75 Awakening

0.50

Recovery after 1 hour infusion

0.25 0.00 0

20

40 Minutes

60

80

FIGURE 38–4  Propofol plasma concentration kinetics. Under the direction of an anesthesiologist, propofol can be used successfully to sedate young children undergoing electrodiagnostic studies. Its major advantage is that it produces a rapid hypnosis. Upon stopping the infusion, the concentration rapidly declines and the child begins to awaken within a few minutes. While the child is sedated, nerve conduction studies, repetitive nerve stimulation studies, and needle electromyography (assessing spontaneous activity) can be performed. As the child begins to awaken, motor unit action potentials can be analyzed.

• Which nerve conduction studies are the fastest and easiest to perform • Which muscles are the easiest to activate and the least painful to study For example, the median motor nerve is much easier to stimulate and record than the tibial motor nerve, which is difficult and painful to stimulate behind the popliteal fossa. Likewise, it is important to choose muscles that are less painful and easier to activate than others. For instance, the first dorsal interosseous (FDI) and the abductor pollicis brevis (APB) both are distal upper extremity C8–T1-innervated muscles. However, the FDI is much less painful to sample than the APB. In children, it is always best to purposefully choose the least painful muscles to examine, unless it is absolutely necessary to examine a muscle that is known to be painful. In addition, it is important to choose muscles that are easy to activate. In children who cannot cooperate, it often is useful to choose muscles that can be activated by withdrawing to a sensory stimulus. For instance, tickling the foot will result in contraction of the tibialis anterior and hamstring muscles as the child reflexively pulls his or her leg away. One of the most important rules in pediatric electromyo­ graphy is: “Take what you can get, when you can get it!” When examining an adult, the electromyographer is accustomed to placing the needle electrode in the muscle, looking first at insertional and spontaneous activity, and then changing the gain to 200 µV per division while having the patient contract to look at the MUAPs. In a child, if one puts the needle electrode into a muscle and MUAPs are firing, do not try to get the child to relax the muscle. It is much more productive to quickly change the sensitivity to 200 µV per division and look at the MUAPs while they are firing, because you might not get another chance!

597

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SECTION VII Electromyography in Special Clinical Settings

Do not expect to follow the same regular routine in a child that you normally would follow in an adult.

GOALS OF THE PEDIATRIC ELECTRODIAGNOSTIC EXAMINATION The goals of the EDX study in infants and children are similar to those in adults. The first goal is to discern if a neuromuscular disorder is present. Differentiating between a central and peripheral cause of weakness is of prime importance to the referring physician. If the problem is peripheral, the next goal is to determine if the pathology is neuropathic, myopathic, or due to a disorder of the neuromuscular junction. This differentiation then allows for a more efficient and logical use of further laboratory testing. If the condition is neuropathic, the next goal is to

determine if motor, sensory, or a combination of fibers is involved. This relies primarily on whether SNAPs are present, reduced, or absent. Take the example of a young child with diffuse denervation and reinnervation on needle EMG associated with low motor amplitudes on nerve conduction studies. Taken together, these findings denote a neuropathic process. If the SNAPs are normal, then the disorder most likely localizes to the anterior horn cells. Although these findings also might be seen in a pure motor neuropathy, this would be very unlikely in an infant or child. On the other hand, if the SNAPs are abnormal, then a peripheral neuropathy likely is present, which has a very different differential diagnosis and prognosis. If a peripheral neuropathy is present, the next important piece of information to discern from the EDX study is whether or not the pathology is demyelinating. Because so many pediatric peripheral neuropathies are genetic in nature and because the demyelinating forms of Charcot–Marie–Tooth

Table 38–4.  Recommended Approach to Childhood Neuromuscular Disorders Diagnostic Test/Procedure Suspected Clinical Diagnosis Duchenne–Becker MD

Option:

1st DNA 1

2nd

3rd

MBx

LGMDs

DNA

MBx

EMG/NCS2

Congenital muscular dystrophies

MBx

DNA

EMG/NCS2

Emery–Dreifuss MD

DNA

MBx

EMG/NCS2

FSH MD

DNA

MBx

EMG/NCS3

MyD

DNA

EMG/NCS

Periodic paralysis/myotonias

DNA

EMG/NCS

Metabolic

MBx

DNA

EMG/NCS3

Congenital myopathies

MBx

DNA4

EMG/NCS5

DM/PM

MRI

MBx

EMG/NCS3

Indeterminate proximal weakness

EMG/NCS

RMNS

MBx/DNA

SMA

DNA

EMG/NCS

MBx6

CIDP

EMG/NCS

CSF

NBx

AIDP (GBS)

CSF

EMG/NCS

HMSNs

EMG/NCS

DNA

Neuromuscular transmission disorders

EMG/NCS

RMNS

Antibodies/DNA7

AIDP, acute inflammatory demyelinating polyneuropathy; BMD, Becker muscular dystrophy; CIDP, chronic inflammatory demyelinating polyneuropathy; CSF, cerebrospinal fluid examination; DM/PM, dermatomyositis/polymyositis; DMD, Duchenne muscular dystrophy; DNA, deoxyribonucleic acid/genetic testing; EMG, electromyography; FSH, facioscapulohumeral; GBS, Guillain–Barré syndrome; HMSNs, hereditary motor and sensory neuropathies; LGMD, limb-girdle muscular dystrophy; MBx, muscle biopsy; MD, muscular dystrophy; MRI, magnetic resonance imaging; MyD, myotonic dystrophy; NBx, nerve biopsy; NCS, nerve conduction studies; RMNS, repetitive motor nerve stimulation; SMA, spinal muscular atrophy. Note that even in the era of molecular diagnostics, electromyography continues to play a prominent role in the evaluation of pediatric neuromuscular disorders. 1. DNA testing is now available for many of the LGMDs. In addition, DNA testing is helpful in a limb-girdle phenotype to also exclude DMD/BMD; 2. In atypical, sporadic cases with low creatine kinase values; 3. Optional; 4. If available; 5. In certain cases, EMG/NCS may be the first option; 6. If EMG/NCS consistent with SMA but DNA test is negative; 7. For congenital myasthenic syndromes. From Darras, B.T., Jones, H.R. Jr., 2000. Diagnosis of pediatric neuromuscular disorders in the era of DNA analysis. Pediatr Neurol 23, 289–300, with permission.

Chapter 38 • Approach to Pediatric Electromyography

disease are the most common, the presence of conduction velocities in the demyelinating range has great importance. Of course, there also are instances of acquired demye­ linating neuropathies in children, which can usually be distinguished from genetic forms of demyelinating neuropathy using the same guidelines that apply to adults (see Chapter 26). In general, there is a very good correlation between the results of EDX studies and the final diagnosis. This is especially true for neuropathic disorders (i.e., anterior horn cell disorders and peripheral neuropathy). They are also helpful but not as good for myopathic disorders, especially in children younger than age 2. As noted earlier, motor units in young children are normally quite small, making the differentiation between normal and myopathic motor unit action potentials very demanding. In addition, some myopathies are fairly “bland” on needle EMG, most often the congenital myopathies. This is in contradistinction to the muscular dystrophies and myositis which are much more easily recognized as myopathic on needle EMG. One might think that in the present era of molecular genetics wherein DNA and other forms of genetic analysis are available for many of the inherited neuromuscular conditions (e.g., spinal muscular atrophy, many of the muscular dystrophies, and many forms of Charcot–Marie–Tooth disease), EDX studies would play less of a role than in the past. This is true for the infant or child who has a classic phenotype of a well-known inherited disorder. In these cases, especially if there is a positive family history, the diagnosis can often be confirmed by genetic testing, without the need for EDX studies. However, this remains a minority of the cases. In the evaluation of a child with weakness or a delay in motor milestones, EDX studies still play a major role in guiding the evaluation process in a logical and efficient manner, with occasional diagnoses made directly from data obtained from EDX studies (Table 38–4). For instance, Dejerine–Sottas syndrome (DSS) is a term applied to a group of genetically heterogeneous demyelinating neuropathies that typically present in infancy or early childhood. DSS can easily mimic the clinical presentation of Werdnig–Hoffman (spinal muscular atrophy type 1).

However, DSS is associated with the slowest conduction velocities ever recorded in humans, typically less than 12 m/s and usually less than 6 m/s. The finding of such a slowed conduction velocity on nerve conduction studies will immediately point to the diagnosis of DSS. Afterward, appropriate genetic testing can be undertaken looking for the known mutations associated with DSS, which include mutations of the P0, MP22, and EGR2 genes, among others. Without doubt, the pediatric EDX study is much more challenging and difficult to perform than a similar study in an adult. However, being aware of the unique maturational and technical issues associated with studying infants and children and approaching the examination with a different philosophy will offer the electromyographer the same kinds of useful information that can be obtained in adults.

Suggested Readings Darras, B.T., Jones, H.R., 2000. Diagnosis of pediatric neuromuscular disorders in the era of DNA analysis. Pediatr Neurol 23, 289–300. Gabreels-Festen, A., 2002. Dejerine–Sottas syndrome grown to maturity: overview of genetic and morphological heterogeneity and follow-up of 25 patients. J Anat 200, 341–356. Hellmann, M., von Kleist-Retzow, J.C., Haupt, W.F., et al., 2005. Diagnostic value of electromyography in children and adolescents. J Clin Neurophysiol 22 (1), 43–48. Jones, H.R., Bolton, C.F., Harper, C.M., et al., 1996. Pediatric clinical electromyography. Lippincott Williams & Wilkins, Philadelphia. Jones, H.R. Jr, De Vivo, D.C., Darras, B.T. (Eds.), 2003. Neuromuscular disorders of infancy, childhood, and adolescence: a clinician’s approach. Butterworth Heinemann, Philadelphia. Parano, E., Uncini, A., DeVivo, D.C., et al., 1993. Electrophysiologic correlates of peripheral nervous system maturation in infancy and childhood. J Child Neurol 8, 336–338. Rabie, M., Jossiphov, J., Nevo, Y., 2007. Electromyography (EMG) accuracy compared to muscle biopsy in childhood. Child Neurol 22 (7), 803–808.

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