2. MATURATIONAL FACTORS
IN PEDIATRIC ELECTRODIAGNOSIS
Peripheral nerve myelination begins at about the
15th week of gestation and continues throughout
the first 3–5 years after birth
Conduction velocities are determined by
myelination, diameter of the fiber, and internodal
differences.
The diameter of the fibers at the time of birth has
been shown to be one-half of that in the adult.
The nodes of Ranvier continue to remodel, with
peak internodal distances being reached at 5 years
of age
3. 1. NERVE CONDUCTION STUDIES
Normal standard adult values for
conduction velocities are reached by age 3
to 5. In infancy, upper and lower extremity
conduction velocities are similar under age 1
Faster conductions are maintained in the
upper extremities and comparatively slower
conductions in the lower extremities, as
with adults. Unique values for expected
conduction velocities are observed for
specific peripheral nerves
4. CONT.
a. Motor Nerve Conduction
Motor conduction velocities in infants are found to be one-
half of adult values. In infants, conduction studies should
be at least greater than 20 m/s. At birth, motor conduction
velocity (MCVs) for the median, ulnar, and peroneal nerves
are 27 m/s.
b. Distal Motor Latency
Distal motor latencies (DMLs) show maturational changes
between infancy and 3–5 years of age, similar to motor
conduction velocities
5. CONT.
c. Compound Muscle Action Potential
Compound muscle action potential (CMAP)
amplitudes are important to consider in the
evaluation of axonal loss, conduction block, and
muscle fiber atrophy
d. Sensory Nerve Conduction
Modern EMG equipment, which includes amplifiers
and signal averaging capability, allows sensory nerve
action potentials to be routinely recorded in the
absence of peripheral nerve pathology
6. CONT.
e. F-waves
The F-wave is a late response that appears as a
supermaximal motor nerve stimulation and arises
from the discharge of a small number of motor
neurons in response to antidromic stimulation of
the motor axon. The F-wave latency is measured
from hand and foot intrinsic muscles, and is useful
for evaluating the motor nerve conduction velocity
and proximal nerve segments.
7. 2. ELECTROMYOGRAPHY
a. Motor Unit Configuration and Amplitude
Amplitudes of motor unit action potentials (MUAPs)
are lower in infants, with amplitudes ranging from
150 microvolts to approximately 2,000 microvolts
b. Motor Unit Duration
Infantile motor unit action potentials are often
shorter in duration. Durations of motor unit action
potentials are often shorter than 5 milliseconds in
infants
8. CONT.
c. In general, as strength of voluntary
contraction increases, there is an increase in
motor unit action potentials recruited.
However, the recruitment pattern in infants
may be disordered and chaotic.
9. STIMULATING ELECTRODES
For neonates and young infants, small stimulators with
short interelectrode distances are commercially
available and simplify the testing of short nerve
segments over small extremities
The stimulation intensity may be reduced by the use of
a small monopolar needle electrode as the stimulating
cathode, with a more proximal surface anode in close
proximity.
Generally, a standard bipolar stimulator may be utilized
for children 6 months of age and older.
10.
11. 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 finger-
clip electrodes may be used.
Motor Conduction
Generally, standard 6-mm silver disc surface electrodes
are used as active and reference electrodes for motor
conduction studies.
12.
13. SPECIFIC CLINICAL PROBLEMS IN
PEDIATRIC ELECTRODIAGNOSIS
Spinal Cord Injury
Neonatal spinal cord injury may occur as an obstetrical complication
or as a result of a vascular insult to the spinal cord.
Typical clinical presentation may include findings of diffuse
hypotonia, possible respiratory distress, hyporeflexia, and urinary
retention.
An anterolateral spinal cord injury due to a vascular insult will
produce EMG findings of severe denervation in diffuse myotomes.
Typically, two to three weeks may lapse before fibrillations and
positive sharp waves are elicited.
Anterior horn cell and axonal degeneration will typically result in
decreased CMAP amplitudes in multiple peripheral nerves.
14. CONT.
Somatosensory evoked potentials SSEPs may help establish a
sensory level in an infant or young child with spinal cord injury,
and is also useful in the evaluation of the comatose or obtunded
child at risk for spinal cord injury without radiographic
abnormality (SCIWORA)
Brachial Plexus and Cervical Nerve Root Lesions
Traumatic obstetrical brachial plexopathy usually results from
traction on the brachial plexus (predominantly upper trunk) and
its associated spinal roots.This can lead to stretching or rupture
of the trunks of the plexus and/or partial axonotmesis or
avulsion of the spinal roots.
15. CONT.
Injury to the upper trunk of the brachial plexus and/or
C5–6 cervical roots is the more common injury known
as Duchenne-Erb’s palsy.
Damage to the lower trunk and/or C8–T1 cervical roots
is referred to as Klumpke’s palsy.
Severe brachial plexus injuries may involve the entire
plexus and C5–T1 nerve roots diffusely.
A Horner’s syndrome due to injury of the C8 andT1
roots and the superior cervical sympathetic ganglion
may be an associated clinical finding.
16. CONT.
Examination should be deferred until at least
three to four weeks after the injury to allow for
abnormal spontaneous rest activity (fibrillations
and positive sharp waves) to develop in the setting
of denervation and axon loss.
Complete injuries are characterized
electromyographically by absent MUAPs (Motor
Unit Action Potential) and absent CMAP
(Compound Muscle Action Potential) amplitudes
in peripheral nerves supplied by the transected
axons.
17. CONT.
The preservation of the CMAP amplitude 10 days or
more after the injury with complete clinical paralysis
suggests that the damage is, in part, a neuropraxic
injury with better prognosis
In perinatal traumatic brachial plexopathy, positive
sharp waves and fibrillations, indicative of true
denervation, can be found by 14 to 21 days after
injury
Absence of fibrillations or positive sharp waves after
this time frame suggests a neuropraxic lesion with
intact axons. In this setting, the prognosis for
recovery is favorable.
