Toxic Neuropathies

Chapter 606 Toxic Neuropathies

Many chemicals (organophosphates), toxins, and drugs can cause peripheral neuropathy (Table 606-1). Heavy metals are well-known neurotoxins. Lead poisoning, especially if chronic, causes mainly a motor neuropathy selectively involving large nerves, such as the common peroneal, radial, and median nerves, a condition known as mononeuritis multiplex (Chapter 702). Arsenic produces painful burning paresthesias and motor polyneuropathy. Exposure to industrial and agricultural chemicals is a less common cause of toxic neuropathy in children than in adults, but insecticides are neurotoxins for both insects and humans, and if they are used as sprays in closed spaces, they may be inhaled and induce lethargy, vomiting, seizures, and neuropathy, particularly with recurrent or long-term exposure. Working adolescents and children in developing countries are also at risk. Puffer fish poisoning, usually by ingestion of even cooked fish meat contaminated with the venom, produces a Guillain-Barré–like syndrome.

Antimetabolic and immunosuppressive drugs, such as vincristine, cisplatin, and paclitaxel, produce polyneuropathies as complications of chemotherapy for neoplasms. This iatrogenic cause is the most common etiology of toxic neuropathies in children. It is usually an axonal degeneration rather than primary demyelination, unlike autoimmune neuropathies.

Chronic uremia is associated with toxic neuropathy and myopathy. The neuropathy is caused by excessive levels of circulating parathyroid hormone. Reduction in serum parathyroid hormone levels is accompanied by clinical improvement and a return to normal of nerve conduction velocity.

Biologic neurotoxins are associated with tick paralysis, diphtheria, botulism, and the variants of paralytic shellfish poisoning. Lyme disease, West Nile virus, leprosy, herpes viruses (Bell palsy), and rabies also produce peripheral nerve– or ventral horn cell–induced weakness or paralysis. Various inborn errors of metabolism are also associated with peripheral neuropathy from metabolite toxicity or deficiencies (Part XI and Table 606-1).