Pediatric Cranial Neuropathies


Age (years)

Number of subjects

Orbicularis oculi

Orbicularis oris

0–1

120

3.1 ± 0.8

5.3 ± 1.7

1–3

91

3.3 ± 0.5

5.4 ± 1.6

3–9

89

3.5 ± 1.0

5.6 ± 1.5

9–15

44

3.5 ± 0.9

5.6 ± 1.7




Table 15.2
Normal facial nerve conduction velocity (meters per second (m/s) ± 2 sd) stimulating CN VII first at a point anterior to the tragus and then at a point along the horizontal portion of the mandible from birth to 15 years
























































































Age

Number of subjects

Cervicofacial branch NCV

0–30 day

18

19.0 ± 2.5

1–2 months

14

21.4 ± 3.4

2–4 months

12

24.5 ± 3.9

4–6 months

24

26.3 ± 2.8

6–8 months

23

29.1 ± 3.3

8–10 months

15

31.7 ± 3.7

10–12 months

14

33.3 ± 3.3

12–18 months

30

36.1 ± 3.0

18 m–2 years

27

37.5 ± 4.7

2–3 years

34

39.5 ± 2.7

3–4 years

16

41.9 ± 4.5

4–5 years

21

43.4 ± 3.3

5–6 years

12

45.5 ± 4.8

6–7 years

12

45.8 ± 5.3

7–8 years

13

46.5 ± 4.1

8–9 years

15

48.1 ± 3.8

9–11 years

17

48.3 ± 2.8

11–13 years

12

48.7 ± 5.6

13–15 years

15

48.5 ± 2.8


NCV nerve conduction velocity

Distances (mm) between stimulation points are 34.6 ± 6.6 up to 12 months, 48.7 ± 9.7 from 1 to 5 years, and 56.1 ± 6 from 5 to 15 years


Electroneuronography (ENOG) uses surface electrodes placed along the nasolabial fold to record a global facial CMAP elicited by a brief supramaximal electrical stimulus applied to the facial nerve at the stylomastoid foramen. The peak-to-peak amplitude of the CMAP is measured bilaterally; an asymmetry greater than 30% is considered abnormal [4]. ENOG is used to evaluate the severity of a lesion to the cranial nerve VII, and has shown prognostic value in complete acute non-traumatic unilateral facial paralysis in childhood [5].



Needle Electromyography of Facial Muscles


Conventional needle EMG contributes to the determination of the characteristics and severity of a lesion to the cranial nerve VII, and gives clues regarding pathogenesis and outcome. Needle EMG examination is performed at rest, and with voluntary contraction or after stimulation. EMG is recorded by a concentric needle electrode in at least one muscle innervated by the temporofacial branch (orbicularis oculi or frontalis), and in another innervated by the cervicofacial branch (orbicularis oris or depressor anguli oris). When tolerated, fasting an infant for up to 4 h before the test may facilitate the recording of bursts of activity arising from the facial muscles while the baby is crying or sucking a pacifier. In older children, voluntary contraction can be recorded after asking the child to imitate the examiner by closing the eyes, smiling, and whistling.

The maximum amplitude of a motor unit potential (MUP) is measured from the highest negative peak to the lowest positive peak of the largest EMG burst. Traces are classified as: (1) normal interference pattern; (2) neurogenic (i.e., single or reduced, high-amplitude MUPs units) or; (3) myogenic (i.e., low-amplitude where the maximum amplitude decreased by at least 30%) (Fig. 15.1). The normal maximum MUP amplitude of the interference pattern is 850 μV (range: 400 μV–1.2 mV) with normal MUP duration from 1 to 2.8 ms. The proportion of polyphasic potentials present in a normal muscle may exceed 30% (Table 15.3) [6].

A395258_1_En_15_Fig1_HTML.jpg


Fig. 15.1
Needle EMG of facial muscles, exemplary recordings: normal pattern (upper trace); low-amplitude pattern, reflecting muscle hypoplasia (middle); neurogenic reduced recruitment (lower trace)



Table 15.3
Needle EMG of muscles of the face, the tongue and soft palate: normal pattern in subjects from 4 days to 3 years old
































Muscles

EMG interference pattern
 
Maximal amplitude (range, mV)

MUPs duration (range, ms)

Proportion of polyphasic MUPs (%)

Orbicularis oculi, Orbicularis oris

0.40–1.2

1–2.8

> 30

Genioglossus

0.38–1.5

1–3.9

> 50

Levator veli palatini, Pharyngoglossus, Palatoglossus.

0.42–1.8

1–3.2

> 50


MUPs motor unit potentials


Blink Responses


This technique explores both facial and trigeminal nerve functions, as well as the pathways between their respective cranial nuclei within the brainstem. The blink reflex results from the contraction of the orbicularis oculi muscle provoked by stimulation of the supraorbital branch of the trigeminal nerve [7]. A single electric shock is applied to the supraorbital foramen to elicit BRs recorded from the orbicularis oculi muscle on both sides. Stimulation of the ipsilateral supraorbital trigeminal nerve provokes a direct response with two components: R1, which is immediate and brief, and R2, which is delayed and longer lasting. Stimulation of the contralateral nerve V provokes a crossed R2 response.

The maturation from birth of the electrically elicited BRs has been studied [8]. The R1 response is always present and its latency achieves normal adult values (range: 9–13 ms) at 44 weeks postmenstrual age. The ipsilateral R2 response can be evoked in most newborns at term birth (latency range: 34–43 ms), but the contralateral R2 response is not always obtained before the age of 8 months. The R1 component corresponds to an oligosynaptic reflex arc involving at least two and no more than three synapses in the pons between the main sensory nucleus of cranial nerve V and the motor nucleus of the ipsilateral cranial nerve VII. The R2 component follows polysynaptic medullary pathways, which are more caudal and closer to the bulbar formations. The spinal trigeminal nucleus has projections to the adjacent paramedian reticular formation and the motor nuclei of both seventh nerves. Injury in the trigeminal pathway leads to delayed or absent ipsilateral R1 and R2 responses, and contralateral R2 response, while a lesion in the facial pathway shows delayed ipsilateral R1 and R2, but normal contralateral R2. Lesions at the pons show ipsilateral abnormal R1 response, while contralateral stimulus has normal R1. Lateral medullary lesions show abnormal R2 response on the affected side, stimulating either the non-affected or the affected side [9].


Neurophysiological Assessment of the Trigeminal Nerve


Methods for studying trigeminal afferents have several limitations. The specific clinical assessment of the ophthalmic, maxillary, and mandibular nerves is not reliable in the young child. Supraorbital sensory nerve action potential has been reported only in normal adults so far [10]. Somatosensory evoked potentials are misleading because electrical stimuli to the orofacial area generate muscle potentials and trigeminal reflexes that contaminate the scalp signal [11]. Trigeminal motor function is clinically assessed by palpating the masseter-temporalis muscles at rest and on voluntary contraction after asking the child to bite down. Transcranial motor evoked potentials are not routinely available in an ambulatory setting, and normal values during growth are not available. Surface electrodes placed over masseter and temporalis muscles enable the analysis of the timing and the envelope of EMG bursts, taking into account that bursts are contaminated with signals generated by facial muscles. Conventional needle EMG of the masseter and temporalis muscles remains the way to study trigeminal motor function and to detect neurogenic abnormalities.



Cranial Nerves IX–X and XII Electrodiagnostic Studies


With the aim to explore bulbar dysfunction and evaluate congenital dysphagia, EMG techniques provide information on brainstem structures involved in oral sensorimotor functions. This includes EMG of muscles of the tongue and soft palate and EMG during bottle-feeding, which investigates the electrophysiology of sucking and swallowing.


The Genioglossus Muscle and the Hypoglossal Nerve


The hypoglossal nerve is purely a motor nerve. Its nucleus consists of a column which extends for nearly the full length of the medulla oblongata. Emerging from the skull by the anterior condylar canal, cranial nerve XII crosses the pharyngomaxillary space and curves anteriorly in the carotid groove. In the sublingual area it sends terminal branches to the ipsilateral muscles of the tongue. The genioglossus is a paired paramedian muscle of the tongue; it can be recorded by the endo-oral route. After local anesthesia by swabbing this area with a small amount of lidocaine (the swab should not contain enough lidocaine for the infant to swallow any drops, as that would entail a risk of side effects from inadvertent ingestion), the needle electrode is inserted in the ventral surface of the tongue, slightly lateral to the midline (Fig. 15.2). The interference pattern is recorded when the infant is crying and also when sucking a nipple. The normal maximal amplitude of the interference pattern is from 380 μV to 1.5 mV (Table 15.3).

A395258_1_En_15_Fig2_HTML.gif


Fig. 15.2
Motor nerve conduction of the hypoglossal nerve stimulus is applied proximally behind the mandible (large arrow #1) and then more distally under the chin (large arrow #2). EMG needle is inserted into the ventral surface of the genioglossus muscle (tongue), just lateral of the midline

For hypoglossal NCSs, electrical stimuli (0.2 ms, 10–40 mA) are applied proximally behind the mandible and then more distally under the chin. The motor response has a polyphasic morphology, a mean duration from 6 to 10 ms, and amplitude from 0.8 to 1 mV. Latencies induced by stimulation under the angle of the mandible do not show a significant change between birth and 15 years, ranging from 2.4 to 4.8 ms (Table 15.4). The hypoglossal NCV increases more than 30% in the first year (Table 15.5).


Table 15.4
Normal motor latency (ms ± 2 sd) of the genioglossus muscle when stimulation is applied to cranial nerve XII behind the mandible from birth to 15 years




























Age (years)

Number of subjects

Genioglossus motor latency

0–1

120

3.8 ± 1.0

1–3

91

3.5 ± 1.1

3–9

89

3.3 ± 0.9

9–15

44

3.4 ± 0.6



Table 15.5
Normal hypoglossal nerve conduction velocity (m/s ± 2 sd) stimulating CN XII behind the mandible and then at distal submental point under the chin from birth to 15 years
























































































Age

Number of subjects

Hypoglossal NCV

0–30d

18

23.5 ± 2.2

1–2 months

14

24.1 ± 2.2

2–4 months

12

26.6 ± 2.7

4–6 months

24

28.9 ± 2.9

6–8 months

23

31.8 ± 3.4

8–10 months

15

34.3 ± 2.9

10–12 months

14

35.7 ± 3.0

12–18 months

30

37.5 ± 2.1

18 months–2 years

27

40.6 ± 2.6

2–3 years

34

42.1 ± 3.0

3–4 years

16

43.5 ± 3.4

4–5 years

21

46.1 ± 2.5

5–6 years

12

46.5 ± 4.9

6–7 years

12

47.3 ± 2.1

7–8 years

13

48.1 ± 6.9

8–9 years

15

49.0 ± 2.6

9–11 years

17

50.2 ± 7.1

11–13 years

12

50.9 ± 6.4

13–15 years

15

50.7 ± 5.4


NCV nerve conduction velocity

Distances between stimulation points (mm) are: 32.5 ± 9.3 up to 12 months, 36.1 ± 6.5 from 1 to 5 years, and 38.2 ± 9.7 from 5 to 15 years


Muscles of the Soft Palate and The Pharyngeal Plexus


The motor fibers of cranial nerves IX and X supplying the muscles of the pharynx arise from the upper part of the nucleus ambiguus. The pharyngeal branches of nerve X merge with the fibers of nerve IX to constitute the pharyngeal plexus, which innervates muscles of the soft palate. The levator veli palatini muscle spreads into the large paramedian section of the soft palate. After local anesthesia by swabbing the mucosa with a small amount of lidocaine, a needle electrode is inserted 1–1.5 cm from the median line. Also, palatoglossus and pharyngoglossus muscles can be easily reached by inserting the needle electrode in the palatoglossal and palatopharyngeal arches respectively. The normal maximal amplitude of the interference pattern in these soft palate muscles is 1.3 mV (Table 15.3).

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Nov 18, 2017 | Posted by in PEDIATRICS | Comments Off on Pediatric Cranial Neuropathies
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