a slowing of conduction on the order of 2–3 meters/
second. Every attempt should be made to maintain extremity temperature with infant warmers, heating lamps, or warm blankets.
Volume Conduction
Volume conduction is defined as the current trans- mission from a potential source through a conducting medium, such as the body tissues. This may produce depolarization of peripheral nerves in proximity to the specific nerve being studied, and this is particularly problematic in smaller children with less soft tissue separating nerves. For example, volume conduction can produce simultaneous stimulation of both the median and ulnar nerves at the wrist or at the elbow. Such volume conduction should always be suspected when higher stimulation intensities or durations are utilized and when CMAP configurations show an initial posi- tive deflection or a multiple peak configuration.
in differentiating a myopathic process (lower recruit- ment frequency values) from a neuropathic process (higher recruitment frequencies after greater than 20–25 Hz). An example of neuropathic recruitment is shown in Figure 7.1.
TECHNICAL FACTORS WITH INFANTILE
Measurement of Distances/
Measurement Error
Distance measurements must be extremely meticulous during pediatric electrodiagnostic evaluations. Segment studies are often on the order of 6–10 cm in length.
A measurement discrepancy of only 1 cm may produce as much as a 10% to 15% conduction velocity error.
Stimulating Electrodes
For neonates and young infants, small stimulators with short interelectrode distances are commercially available and simplify the testing of short nerve seg- ments over small extremities (Fig. 7.2). The stim- ulation intensity may be reduced by the use of a small monopolar needle electrode as the stimulating
Shock Artifact
Shock artifact is a common problem with smaller sub- jects because of short distances between the stimula- tor and recording electrodes. This may be particularly problematic with distal stimulation. The ground elec- trode should be placed between the stimulating and recording electrodes, and, in infants, often a standard 6-mm silver disc or ring electrode can be placed around the wrist or ankle. Alternatively, the ground disc may be taped to the dorsal surface of the hand. Other approaches to minimize shock artifact in young chil- dren include the utilization of pumice paste to reduce skin impedance and permit suprathreshold stimula- tion with lower electrical currents, use of a minimal amount of conduction gel or cream, and rotation of the proximal anode in relation to the distal cathode.
7.6
Normal F Wave Latencies in Children (msec)MEDIAN (REF.) ULNAR (REF.) PERONEAL (REF.) TIBIAL (REF.) 24–72 hours 19.56 ± 2.44 (w) (9)
16.51 ± 1.74 (e) (9)
19.67 ± 2.74 (w) (9) 16.64 ± 1.30 (e) (9)
27.56 ± 3.82 (a) (9) 24.38 ± 3.74 (k) (9)
26.92 ± 3.27 (a) (9) 23.51 ± 2.45 (k) (9) 7 days–1 month 18.17 ± 2.17 (w) (10) 18.63 ± 1.6 (w) (10) 25.2 ± 4.82 (a) (10) 23.92 ± 1.62 (a) (10) 0–3 months 17.62 ± 1.39 (w) (9)
15.39 ± 1.46 (e) (9)
17.65 ± 1.39 (w) (9) 14.93 ± 1.80 (e) (9)
26.14 ± 2.84 (a) (9) 23.46 ± 2.76 (k) (9)
28.59 ± 2.41 (a) (9) 22.52 ± 2.10 (k) (9) 4–6 months 17.54 ± 1.96 (w) (9)
15.41 ± 1.56 (e) (9)
16.99 ± 1.24 (w) (9) 14.91 ± 1.28 (e) (9)
25.18 ± 4.37 (a) (9) 22.15 ± 2.68 (k) (9)
23.93 ± 1.85 (a) (9) 20.67 ± 2.30 (k) (9) 1–6 months 15.91 ± 1.22 (w) (10) 15.71 ± 1.6 (w) (10) 21.4 ± 1.78 (a) (10) 21.4 ± 1.35 (a) (10) 6–12 months 16.86 ± 1.50 (w) (9)
14.37 ± 1.17 (e) (9) 15.67 ± 0.89 (w) (10)
17.02 ± 1.45 (w) (9) 14.41 ± 0.88 (e) (9) 15.45 ± 1.37 (w) (10)
25.54 ± 2.04 (a) (9) 21.56 ± 3.36 (k) (9) 20.33 ± 1.1 (a) (10)
23.78 ± 1.83 (a) (9) 20.92 ± 1.59 (k) (9) 22.0 ± 2.05 (a) (10) 1–2 years 15.64 ± 1.08 (w) (10) 15.67 ± 0.78 (w) (10) 22.82 ± 1.66 (a) (10) 24.21 ± 1.63 (a) (10) 1–3 years 16.41 ± 1.13 (w) (9)
14.21 ± 0.77 (e) (9)
16.63 ± 1.88 (w) (9) 14.69 ± 1.35 (e) (9)
26.73 ± 2.87 (a) (9) 24.30 ± 2.46 (k) (9)
25.44 ± 2.20 (a) (9) 23.65 ± 1.71 (k) (9) 2–4 years 16.36 ± 1.45 (w) (10) 16.0 ± 1.41 (w) (10) 24.64 ± 2.21 (a) (10) 25.6 ± 2.53 (a) (10) 4–6 years 17.62 ± 1.62 (w) (9)
15.81 ± 1.17 (e) (9) 18.0 ± 1.27 (w) (10)
18.51 ± 1.74 (w) (9) 16.53 ± 1.48 (e) (9) 18.25 ± 1.48 (w) (10)
30.57 ± 3.82 (a) (9) 25.22 ± 3.44 (k) (9) 29.45 ± 2.58 (a) (10)
31.07 ± 3.10 (a) (9) 25.97 ± 2.32 (k) (9) 30.12 ± 2.52 (a) (10) 6–14 years 20.18 ± 1.61 (w) (9)
17.34 ± 1.52 (e) (9)
20.66 ± 1.92 (w) (9) 18.14 ± 1.46 (e) (9)
38.16 ± 4.43 (a) (9) 31.38 ± 4.75 (k) (9)
36.32 ± 3.72 (a) (9) 32.78 ± 3.89 (k) (9) 18–30 years 26.14 ± 3.03 (w) (9)
22.88 ± 1.34 (e) (9)
27.03 ± 2.14 (w) (9) 23.42 ± 1.90 (e) (9)
49.63 ± 7.74 (a) (9) 41.23 ± 7.63 (k) (9)
48.27 ± 3.09 (a) (9) 39.93 ± 2.73 (k) (9) Side-to-side
difference
1.03 ± 0.73 (2.5) 0.94 ± 0.69 (2.3) 1.19 ± 1.17 (3.5) 1.26 ± 1.01 (3.3)
Data are presented as means ± SD Minimum F-wave latency from 10 recordings
w, wrist stimulation; e, elbow stimulation; a, ankle stimulation; k, knee stimulation Side-to-side difference shows mean ± SD (upper limits of normal)
TIBIAL MEDIAN ULNAR 17.37 ± 1.23 18.67 ± 1.71 (w) (25/25)
15.81 ± 1.15 (e)
18.66 ± 1.48 (w) (25/25) 16.24 ± 0.93 (e)
0–3 months 16.01 ± 1.23 17.15 ± 0.92 (w) (12/20)
14.99 ± 0.94 (e)
17.25 ± 1.93 (w) (9/20) 15.08 ± 1.85 (e)
4–6 months 15.73 ± 1.19 16.95 ± 1.12 (w) (12/20)
14.64 ± 0.82 (e)
16.74 ± 0.77 (w) (7/20) 14.68 ± 0.67 (e)
6–12 months 15.92 ± 1.28 15.75 ± 1.14 (w) (7/20)
14.23 ± 0.51 (e)
16.49 ± 1.01 (w) (4/20) 14.32 ± 0.50 (e)
1–3 years 16.91 ± 1.46
4–6 years 18.76 ± 1.71
7–14 years 22.00 ± 1.97
18–30 years 28.04 ± 1.68
Side-to-side difference 0.56 ± 0.37 (1.3) Data are presented as means ± standard deviation (SD)
The tibial H-reflex was elicited by submaximal intensity of stimulus over the posterior tibial nerve at the knee with recording over the soleus distally measured half the distance from the stimulation point to the medial malleolus.
The median and ulnar H-reflex was elicited in infants with proportions showing a response shown in parenthesis.
Side-to-side difference shows mean ± SD (upper limits of normal) Source: Ref. 9.
7.7
Normal H Refl ex Latencies in Children (msec)Figure 7.1 Neuropathic recruitment of the deltoid in a 12-month-old child with a brachial plexus injury sustained at birth. The initial recruited motor unit action potential is 2,500 μV, and it is fi ring at 25 Hz.
cathode, with a more proximal surface anode in close proximity. For example, for ulnar orthodromic sen- sory studies, the author has utilized ring electrodes on the fifth digit and recording electrodes over the ulnar nerve at the elbow. Generally, a standard bipo- lar stimulator may be utilized for children 6 months of age and older.
Recording Electrodes
Sensory Conduction
Generally, sensory nerve action potentials are easily recorded in newborns. The standard ring electrodes, needle recording electrodes, and/or pediatric-size fin- ger-clip electrodes may be used. While for adults, a
peroneal, tibial, facial, and phrenic motor nerves and the median, ulnar, and sural sensory nerves.
Stimulation of the posterior tibial nerve (recording abductor hallucis brevis) produces a discrete CMAP more commonly than stimulating the peroneal nerve (recording over extensor digitorum brevis). The exten- sor digitorum brevis (EDB) muscle may be difficult to visualize or palpate in infants. Its CMAP configura- tion frequently has either an initial positivity or a low broad configuration. In addition, the CMAP ampli- tude may change substantially with slight changes in position for the active electrode over the extensor digitorum brevis.
The axillary and musculocutaneous motor nerve conduction studies may be helpful in the setting of infantile brachial plexopathy. Care should be taken to minimize volume conduction. Often, the intact side is used for amplitude comparisons.
Evaluations of proximal nerves, such as the axil- lary spinal accessory musculocutaneous and femoral, are often useful in the evaluation of severe demyelin- ating neuropathies (Fig. 7.4). The distal latencies of these nerves may be severely prolonged on the set- ting of severe reductions in the CMAPs of more distal nerves due to conduction block or axon loss.
Percutaneous stimulation of the phrenic nerve is performed with techniques similar to that uti- lized in the adult, with stimulation performed at the posterior border of the sternocleidomastoid at the level of the thyroid cartilage or alternatively just medial (or occasionally lateral) to the sternal head of the sternocleidomastoid. Recording electrodes may be placed in the fifth to sixth intercostal space 2 cm apart at the anterior axillary line, or alter- natively an active electrode may be placed imme- diately below the costal margin at the level of the nipple with recording electrode at the xiphoid. The active electrode may need to be moved to adjacent 4-cm interelectrode distance is optimal, this is not pos-
sible in small children. Hence, the pediatric electrodi- agnostic clinician should attempt to obtain as much distance as possible between active and reference electrodes. Every attempt should be made to obtain at least a 2-cm interelectrode distance. Stimulation of the digits, palm, or wrist, with electrodes located more proximally at the elbow for median and ulnar sensory studies provide longer distance and less measurement error. In general, normative data for sensory nerve con- duction velocities are more readily available than nor- mative data for distal latencies at specific distances.
Motor Conduction
Generally, standard 6-mm silver disc surface electrodes are used as active and reference electrodes for motor conduction studies. Some electrode diagnosticians pre- fer the use of ring electrodes on digits as the reference electrode and a standard surface electrode over the Moro point at the muscle as the active electrode (Fig. 7.3).
Often, 4–6-cm distances are used from the stimulator to active electrode. Conduction velocities and CMAP amplitudes are generally more relevant data in infants than motor distal latencies because distal nerve entrap- ments are rare. Thus, the distances used from distal stimulation to active electrode are less critical.
Special Considerations for Nerve Conduction Studies
The best normative data for pediatric nerve con- duction studies are available for the median, ulnar, Figure 7.2 Pediatric nerve stimulator (A). The interelectrode distance between cathode and anode is less than
2 centimeters (B).
Figure 7.3 Recording electrodes for a median motor nerve conduction study in a small child. The active electrode is placed over the abductor pollicis brevis on the thenar eminence. The recording electrode is a ring electrode placed on the index fi nger. The ground electrode is a 6-millimeter silver disc electrode placed on the back of the hand.
B A