On electrophysiological testing, motor conduction velocities and sensory nerve conduction remain normal. Compound muscle action potentials from affected muscles are diminished [84] . High frequency repetitive nerve stimulation produces an incremental muscle response similar to the Eaton-Lambert syndrome [85] . Autonomic function studies show an absent sympathetic skin response and significantly decreased heart rate variation [86] . Differential Diagnosis. Botulism may be confused with Guillain-Barré syndrome (especially the Miller Fisher variant), myasthenia gravis, or a pontine stroke. Furthermore, the differential diagnosis includes drug intoxication, poliomyelitis, tick paralysis, diphtheria, and paralytic shellfish poisoning. Botulism and atropine poisoning can both cause dilated pupils, dry mouth, constipation, urine retention, and prompt vomiting after food ingestion.