Neurotoxic Changes with Crotalid Envenomation

Fasciculations and paresthesias are frequent seen with rattlesnake envenomation, with respective occurrences of 33% and 63%. A common complaint following bites by the Southern Pacific rattlesnake (C. viridis helleri), and sometimes reported after other pit viper biters, is tingling or numbness over the tongue and mouth or scalp, fingers and toes, and around the wound. Two syndromes of neurotoxicity following rattlesnake envenomation have been described. Myokymia, or muscle fasciculations, may occur following enveno-mation by various species of rattlesnakes, including Southern Pacific rattlesnakes, western diamondback rattlesnakes (C. atrox), and timber rattlesnakes (C. horridus horridus) (26,47,48).

Another type of neurotoxicity, described following envenomation by certain populations of Mojave rattlesnakes (C. scutulatus scutulatus), may manifest with generalized weakness, cranial nerve palsies, and respiratory paralysis. Venom of the Mojave rattlesnake, unlike the venom of other rattlesnakes, does not usually produce a significant coagulopathy. It also produces far less tissue destruction than most other rattlesnake venoms (26,48,49).

Mojave venom A is found in snakes inhabiting California, Utah, and southwestern Arizona. It contains Mojave toxin, which can produce a systemic neu-rotoxic syndrome with lethargy, obtundation, neuromuscular weakness, cranial nerve dysfunction, and respiratory paralysis in the absence of local symptoms. Mojave toxin acts presynaptically, inhibiting the frequency of miniature endplate potentials and indirectly evoked muscle contraction without affecting muscle responses to direct stimulation or to acetylcholine (50-52).

Mojave rattlesnakes not expressing Mojave toxin (type B snakes, generally located in the area between Tucson and Phoenix) are characterized by hemorrhagic and proteolytic venom peptides that type A snakes lack, and they cause local tissue findings similar to those of other North American crotalids. Mojave toxin has also been isolated in venom of western diamondback rattlesnakes and prairie rattlesnakes (51,53).

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