Pyridostigmine toxicity. Electrophysiological study

A 54-year-old neurotic patient developed pyridostigmine-induced proximal weakness with daily 3600 mg of pyridostigmine. Detailed analysis of the RNS test showed three different types of responses which were reproduced in the in vitro nerve-muscle preparation, confirming that three different responses represent the different degree of pyridostigmine toxicity. One of responses was a pattern, thought to be typical of anticholinesterase toxicity: repetitive discharge and the maximal decrement in the second response followed by an increment (dip phenomenon). With reduction of pyridostigmine, clinical and electrophysiological improvement followed.