I suspect toxic neuropathy is more common than is generally believed; it may be due to environmental exposure in some cases (and the Washington University Neuromuscular website certainly has a massive database of chemicals known to be neurotoxic) but I believe far more of it is iatrogenic--caused by medical interventions, particularly pharmaceutical ones.

And yes, unfortunately in a lot of these cases the neurotoxicity of the drugs does not show up quickly, but only with steady dosing over longer periods, so it doesn't usually show up as a prominent side-effect in the shorter clinical trials. With drugs designed to be taken for lifetime chronic conditions, it may not be noticeable for years or even decades. Drugs like the heavy metal anti-cancer meds (i.e., cisplatin) are notoriously neurotoxic because their effects show up rather quickly, but as has been mentioned, we are seeing neurotoxic effects with long-term taking of statins. These effects would have been hard to pick up in the original trials. And I suspect that we may one day find other neurotoxicities from other long term drugs or long-term small quantity chemical exposures (contrast the sudden effects of Agent Orange with the slow effects of phthalates).