FACIAL PARALYSIS IN THE NEONATE
Facial paralysis or an asymmetric fades is a common finding in the neonate. This may be due to acquired traumatic facial palsy (a common iatrogenic problem with forceps deliveries), central nervous system conditions, congenital facial palsy, and congenital hypoplasia of the depressor anguli oris muscle. Differentiating developmental from traumatic facial paralysis noted at birth is important for determining prognosis, but also for medicolegal reasons. Facial NCSs aid in diagnosis (82). Side-by-side comparisons of amplitudes and latencies are essential. CMAP amplitude reduction and prolonged latency on the involved side indicate facial nerve involvement. Brainstem auditory evoked potentials and blank reflexes may be helpful in determining central nervous system involvement. Axonal integrity can be determined by electromyographic evaluation for spontaneous activity and motor unit recruitment. Improvement on serial testing provides favorable prognostic information, particularly when improvement occurs over 1 to 2 weeks. Normal facial nerve distal latencies in the newborn are less than or equal to 12.0 msec; in children 1 to 12 months less than or equal to 10.0 msec; in children 1 to 2 years of age less than or equal to 6.3 msec; in children 2 to 3 years of age less than or equal to 4.5 msec; in children 3 to 4 years less than or equal to 4.0 msec; and less than or equal to 5.0 msec in children older than 4 years of age (83).
Asymmetric crying fades (ACF) is congenital hypoplasia of the depressor anguli oris muscle characterized by asymmetry of lower lip depression during crying. This has an overall incidence of 0.6%. One recent study determined the incidence of ACF in a large population of patients with 22qll.2 deletion to be 14% (84). Associated palatal anomalies were common (77%), as was congenital heart disease (78%). It is suggested that newborns with ACF be referred for further screening for the 22qll.2 deletion syndrome.
Hereditary Neuropathies (Charcot-Marie-Tooth [CMT] Subtypes)
Clinical findings associated with hereditary neuropathies and the current classification of these disorders are described in Chapter 18. The demyelinating form (CMT 1) typically has onset in early childhood. Marked slowing of MCVs, usually to less than 50% of normal is usually present in early childhood (85-87). Generally, marked swelling of motor NCVs is present by 3 to 4 years of age (84). Distal latencies are usually severely prolonged. There is usually less temporal dispersion than observed in AIDP (GBS) due to fairly uniform demyelination of all axons. Needle EMG abnormalities include defibrillation with positive sharp waves, decreased interference pattern, and large-amplitude polyphasic MUAPs resulting from reinnervation by collateral axonal sprouting.
CMT 2 is the axonal form. CMAP and SNAP amplitudes may be reduced, but NCVs are either in the low normal range or mildly reduced. Needle EMG shows evidence of chronic denervation and reinnervation. CMT 3 is also referred to as Dejerine-Sottas disease and congenital hypomyelinating neuropathy which usually present in infancy. CMAP amplitudes are reduced due to a combination of conduction block and axonal loss, motor NCVs are typically less than 10 m/s, and latencies may be three times the normal value (88).
Acute Inflammatory Demyelinating Polyradiculoneuropathy (GBS)
These children often present with an acute rapid ascending paralysis initially affecting the lower limbs. While pain is common, sensory symptoms are usually mild and objective sensory loss is fairly rare. Electrophysiologically, criteria for poor recovery in adults may not apply to children. One study documented good recovery in children with low median CMAPs and fibrillation potentials (89), while another study showed no difference in the incidence of reduced CMAP amplitude among ventilated and nonventilated children (74). It has been noted that gait disorder, leg pain, a high rate of distal conduction block (decreased distal CMAP amplitudes), and a good prognosis are among the main specific features of GBS in childhood (90).
Classic electrophysiologic findings in GBS include prolonged or absent F-waves early in the course of the disorder, slowing of CVs, both proximally and distally, prolonged distal latencies, reduced CMAP amplitudes with evidence of conduction block, and significant temporal dispersion (see Figure 6.10) (91). The electrophysiologic findings may lag behind the clinical signs and symptoms. In addition, electrophysiologic recovery may lag behind clinical recovery.