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Ebook Neuromuscular disorders (2/E): Part 2

(BQ) Part 2 book “Neuromuscular disorders” has contents: Toxic neuropathies, neuropathies associated with endocrinopathies, idiopathic polyneuropathy, autoimmune myasthenia gravis, muscular dystrophies, congenital myopathies, metabolic myopathies, mitochondrial disorders, and other contents. | CHAPTER 20 Toxic Neuropathies This chapter reviews neuropathies associated with various drugs and other environmental exposures (Table 20-1). Toxic neuropathies due to chemotherapeutic agents are discussed in Chapter 19. The associated neuropathy for most of these is an axonal, length-dependent predominantly sensory neuropathy. The history of exposure and sometimes the involvement of other organ systems help to suggest the correct diagnosis. Although we mention features that have been reported on nerve biopsy, this is not typically part of the workup as in most cases the abnormalities are nonspecific. ►► TOXIC NEUROPATHIES ASSOCIATED WITH MEDICATIONS Pathogenesis The pathogenic basis of the neuropathy is not known. Some have found that metronidazole binds to DNA and/or RNA, which could lead to breaks and impair transcription or translation to normal proteins.7,8 Others have speculated that toxicity may arise from the production of nitro radical anions that bind and disrupt normal protein/enzyme function.8 Furthermore, the histological abnormalities in metronidazole-treated rodents and abnormalities on brain MRI scans in patients with metronidazole-associated encephalopathy resemble thiamine (vitamin B1) deficiency. It has been postulated that there may be enzymatic conversion of metronidazole to an analog of thiamine, which may act as a B1 antagonist.9 METRONIDAZOLE MISONIDAZOLE Clinical Features Clinical Features Metronidazole is used to treat a variety of protozoan infections and Crohn disease.1–8 Metronidazole is a member of the nitroimidazole group and has been associated with hyperalgesia and hypesthesia in a length-dependent pattern. Autonomic dysfunction may develop as well. Motor strength is typically normal. The cumulative dose at which neuropathy occurs is wide, ranging from 3.6 to 228 g. Although there is no clear dose effect, neuropathy appears to occur more frequently in patients receiving greater than 1.5 g daily of metronidazole for 30 or .