Facial Paralysis in the Neonate
Facial paralysis or an asymmetric facies 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.
Facial nerve conduction studies aid in diagnosis (68). Side-to-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 one to two weeks. Normal facial nerve distal latencies in the newborn are mZs. Note the conduction block (amplitude drop from 2.734 to 0.260 mV) and temporal dispersion.Krabbe disease is associated with marked central and peripheral demyelination, and NCS typically show a mixed sensorimotor demyelinating peripheral neuropathy. The peripheral neuropathy occurs early in the neonatal period in Krabbe disease and affects the nerves uniformly. Nerve conduction studies may provide a highly sensitive tool to screen this patient population (78).
In ataxia telangiectasia, there is a loss of large, predominantly sensory, myelinated fibers due to a primary axonal degeneration. In Friedreich’s ataxia, an autosomal recessive condition, there is a primary axonal degeneration of peripheral nerve fibers producing reduced or absent sensory compound action potential amplitudes.
Acquired Toxic Neuropathies
Toxic polyneuropathies with predominantly axonal involvement include lead-, mercury-, and vincristine- induced neuropathy, among others.
Predominantly demyelinating neuropathies may be caused by organophosphate poisoning and arsenic poisoning. While arsenic poisoning may clinically simulate Guillain- Barre syndrome or chronic inflammatory demyelinating polyneuropathy (CIDP), electrophysiologic studies have shown evidence of both axonal degeneration and severe demyelination.Burn-Associated Neuropathies
Children and adults with extensive burns are at increased risk for mononeuropathies and/or peripheral neuropathies (79-84). Mechanisms include direct nerve tissue destruction from the burn, extensive edema with compartment syndrome, critical illness polyneuropathy caused by systemic mediators, and entrapment neuropathies caused by scarring during and/or after healing. The incidence of neuropathy exceeds 10% in many series. Burn-associated polyneuropathy (BAPN) is common after thermal injury, and the electrophysiologic manifestations of BAPN are usually present within the first week (81). Thermal injuries may induce an inflammatory cascade that results in alterations of nerve function. In one series, those with severe neuropathy had higher levels of C-reactive protein (81). Other risk factors associated with a significantly higher prevalence of neuropathy include age above 20 years, electric burns, burns involving full thickness of the skin, a surface area of more than 20%, history of alcohol abuse, and number of days in the intensive care unit. In animal models of burn injury, both functional and morphological deficits are produced in peripheral nerve axons at sites well removed from a full-thickness dermal burn injury (85). The neural deficits may contribute to changes in neuromuscular transmission and the development of limb and respiratory muscle weakness that also accompany burn injury. Further animal work has demonstrated that burn wound excision at 30 minutes but not at 3 hours prevented the nerve conduction deficits measured in mice with 20% body surface area burns (86). The cellular basis of burn-induced neuropathy is unknown, but nitric oxide and tumor necrosis factoralpha appear to play a role.
Diabetic Polyneuropathy
Nerve conduction velocity (NCV) in the distal motor and sensory nerves, the motor nerve distal latency, and the sensory nerve action potential (SNAP) amplitude were impaired in adolescent patients with type 1 diabetes. The deterioration in motor NCV, H-reflex latency, and SNAP amplitude became more conspicuous in late puberty and postpuberty, and was related to poor metabolic control (87). In another study of children 7 to 20 years old with a duration of diabetes of more than 3 years, 57% of the patients had abnormal conduction, which was seen most often in the motor nerves, especially in the peroneal nerve (41%), followed by the median nerve (24%) (88).