Botulinum toxin is produced by the anaerobic bacteria gram positive bacillus Clostridium botulinum and exerts its pathogenic influence by blocking acetylcholine release at neuromuscular junctions. This causes a flaccid, descending paralysis. Early symptoms include blurry vision, followed by minimally reactive, dilated pupils, ptosis, and diplopia, in addition to dysarthria and dysphagia. The disease progresses distally to involve weak neck muscles which strain to hold the head up, weakening of the arms, respiratory musculature, and finally the legs, in a symmetrical fashion, until flaccid paralysis sets in. Deep tendon reflexes are reduced. The patient remains afebrile and with a clear sensorium. Common sources are contaminated home-canned vegetables, especially green beans, garlic in oil, fermented fish, and improperly stored foods, including previously cooked, but now room temperature, tin-foil wrapped baked potatoes.

Botulism can be differentiated against GBS which has ascending flaccidity (starting with paresthesia and weakness in the distal legs and progressing upwards), sensory involvement, absent DTR's, and normal pupils. Botulism can also be differentiated from Myasthenia Gravis, which causes weakness of muscles which fatigue with repetition and recover with rest, ptosis that worsens throughout the day, normal pupils, and normal reflexes. All three disease states have in common a clear sensorium and no fever.