Electrophysiologic methods as an aid in diagnosis of botulism: a review.

Electrophysiologic studies can be of help to the clinician in establishing the diagnosis of botulism. This is particularly true when serologic and toxologic confirmation cannot be obtained. Among the situations in which laboratory confirmation is lacking are cases diagnosed late and some cases of wound botulism. The expected electrophysiologic findings in botulism are as follows: (1) There is almost always a small evoked muscle action potential in response to single supramaximal nerve stimulation. (2) Post-tetanic facilitation is similar to, but less notable, than that seen in the Lambert-Eaton syndrome. (3) Postactivation exhaustion is not prominent. (4) The decremental response of muscle action potential to slow rate of stimulation is absent or not notable. (5) Single-fiber electromyographic studies reveal increased jitter and blocking. Jitter is frequency dependent and decreases with higher discharge rates. Fiber density values are lowered.