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 GBS or chronic 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 (96-101). 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 (98). 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 (98). Other risk factors associated with a significantly higher prevalence of neuropathy include age above 20 years, electrical 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 (ICU). 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 (102). The neural deficits may contribute to changes in neuromuscular transmission and the development of limb and respiratory muscle weakness that also accompanies 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 (103). The cellular basis of burn-induced neuropathy is unknown, but nitric oxide and tumor necrosis factor-alpha (TNF-alpha) appear to play a role.

Vitamin D deficiency has been reported in pediatric burn patients (104), and the available literature on vitamin D status in burn patients has been reviewed. Vitamin D deficiency has been demonstrated to result in itching, muscle weakness, and neuropathy, all of which are common postburn sequelae. The major source of vitamin D is synthesis in the skin with a small amount being absorbed through dietary intake. Population groups are at higher risk of vitamin D deficiency if they have inadequate exposure to ultraviolet (UV) light or reduced biosynthetic capability due to skin damage. Burn patients fall into both risk groups and also suffer common complaints that overlap with those reported by patients with vitamin D deficiency.

Diabetic Polyneuropathy

NCV in the distal motor and sensory nerves, the motor nerve distal latency, and the 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 (105). 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%) (106).

Neuropathies Associated With Infections

HIV INFECTION. Children with HIV may develop a variety of neurologic sequelae including encephalopathy, progressive multifocal leukoencephalopathy, myelopathy, intractable seizures, optic neuritis, acute vasculitis, hemiplegia, paraspinal lymphoma, and peripheral nerve disease. The peripheral nerve dysfunction may present as distal symmetric sensory or sensorimotor polyneuropathy, carpal tunnel syndrome (CTS), lumbosacral polyradiculopathy, motor neuronopathy, AIDP and CIDP, autonomic neuropathy, sensory ganglionopathy, and toxic neuropathy (caused by antiretroviral medications) (107). In addition, polyradiculopathy and multiple mononeuropathies may be caused by other infections (eg, cytomegalovirus, hepatitis B or C, and herpes zoster). In one series, one-third of children 5 to 14 years of age had symptoms and signs of peripheral nerve involvement. Distal paresthesia and/ or pain plus diminished ankle jerks and/or diminished vibration sense were the most common clinical findings. Symptoms were chronic and fluctuating, and pain was, in general, not severe. NCSs primarily revealed axonal changes (108). The issue of peripheral nerve involvement may be multifactorial. Children with HIV-1 infection are exposed to antiretroviral (ARV) drugs for an ever-increasing length of time throughout postnatal growth and development, and the cumulative toxicities are becoming progressively apparent. Evidence for nucleoside reverse transcriptase inhibitor (NRTI) associated mitochondrial toxicity is seen in vitro, in animal models and in NRTI-exposed adults and children (108). Peripheral neuropathy is associated with the chronic use of dual NRTI regimens in HIV-infected children, and regimens containing Zidovudine (Retrovir, AZT, ZDV) have less toxicity than do those containing d4T (109).

LYME DISEASE. Lyme disease is the most common tick-borne disease in the United States. Children and those spending extended time outdoors in wooded areas are also at increased risk. The spectrum of neurologic manifestations and the relative frequencies of different syndromes associated with North American Lyme disease caused by Borrelia burgdorferi infection have been reviewed in a series of 96 children referred for neurologic problems in association with the infection (110). The most frequent neurologic symptom was headache, and the most common sign was facial palsy. Less common manifestations were sleep disturbance, and papilledema associated with increased intracranial pressure. Signs and symptoms of peripheral nervous system involvement are infrequent. Cranial neuropathy is common (111) and children may present with only cranial neuropathy, both cranial neuropathy and other neurologic symptoms, and neurologic symptoms without cranial neuropathy. Patients with Lyme meningitis had statistically more frequent cranial neuropathy (73% vs. 4%) (112). In Lyme disease, the most common clinical syndromes include mild encephalopathy, lymphocytic meningitis, and cranial neuropathy (facial nerve palsy). In contrast with adult patients with neurologic Lyme disease, meningoradiculitis (Bannwarth's syndrome) and peripheral neuropathy syndromes are rare in children.

 
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