Toxic Neuropathies

Several toxic agents have an easy access to the peripheral nervous system. These toxic substances belong to different classes, including therapeutic drugs, recreational abuse substances, environmental and industrial contaminants. Establishment of a real causal relationship between peripheral nervous system damage and toxic agents exposure is obvious in some condition (e.g., in the course of anticancer chemotherapy), but it can be very difficult or even misleading in other contexts, when potential exposure is not easy to be proven or is not reported by the affected subjects. Not all the reports describing the peripheral toxicity of substances causing rare events are convincing, and the list of putative neurotoxic agents is probably over-estimated. Nevertheless, relationship even with agents with only occasional neurotoxicity has been clearly established. The clinical effects of the exposure to neurotoxic agents are highly variable, depending on the mechanism of their action and on the intracellular target. In most cases, sensory impairment is exclusive or largely predominant over motor or autonomic damage. Similarly, the clinical course may be acute, subacute, or chronic and recovery after withdrawal from toxic exposure is not always guaranteed. Moreover, worsening lasting months after the suspension of toxic exposure (the “coasting effect”) has also been reported. Despite the typical clinical features are those of distal, symmetrical polyneuropathy, local application of neurotoxic agents may induce focal mononeuropathies.