Neurotoxicity Associated With the Southern Pacific Rattlesnake (Crotalus helleri) Michael Levine, MD*; David Tashman, MD; Ian Recchio; Nathan Friedman, MD; Justin Seltzer, MD; Alicia Minns, MD; Frank LoVecchio, DO, MPH *Corresponding Author. E-mail: michaellevine@mednet.ucla.edu. The Southern Pacific rattlesnake (Crotalus helleri) is commonly encountered throughout Southern California. Typical toxicity includes tissue injury and hematologic toxicity. However, neurotoxicity is not commonly reported with rattlesnake envenomations, other than infrequently with select species, including the Mojave rattlesnake (Crotalus scutulatus scutulatus). Importantly, clinical neurotoxicity has not been well described with the Southern Pacific rattlesnake, the only rattlesnake in the city of Los Angeles, along with the Southern and coastal regions of Los Angeles County. In this case series, 7 patients envenomated by the Southern Pacific rattlesnake with significant neurotoxicity, including dysarthria, ataxia, and myokymia, are presented. Clinicians practicing in this region should be aware of evolving patterns of toxicity associated with the Southern Pacific rattlesnake. [Ann Emerg Med. 2022;-:1-5.] 0196-0644/$-see front matter Copyright © 2022 by the American College of Emergency Physicians. https://doi.org/10.1016/j.annemergmed.2022.08.020 INTRODUCTION The Southern Pacific rattlesnake (Crotalus helleri) is a common species throughout Southern California and is the only native rattlesnake species found within Los Angeles City limits, Southern Los Angeles County, and the coastal regions (eg, Malibu). The snake resides in diverse habitats, including coastal dunes, foothills, grasslands, montane forests, and desert habitats. Consequently, it is frequently encountered by the casual hiker or homeowner. Human interactions with Southern Pacific rattlesnakes are common as the species’ range overlaps with densely populated areas. Approximately 5,000 venomous snakebites are reported to US Poison Control Centers annually. 1 Among these, rattlesnakes account for a sizable percentage and are arguably some of the most dangerous of all native North American snakes. Toxicity from rattlesnakes generally consists of local tissue injury and hematologic toxicity, including thrombocytopenia, coagulopathy, and/or hypofibrinogenemia. 2,3 In addition, neurotoxicity has been classically associated with envenomation from the Mojave rattlesnake (C. scutulatus scutulatus), whereas myokymia, a unique contraction of the muscles resembling a rippling or wave appearance, has been infrequently described in the Southern Pacific, timber rattlesnake (Crotalus horridus horridus), and rarely the midget faded rattlesnake (Crotalus viridis decolor). 4,5 Significant neurotoxicity, including dysarthria, weakness, and ataxia, has rarely been described. Historically, among North American snakes, neurotoxicity has been nearly exclusively associated with a subset of the Mojave rattlesnake containing Mojave A toxin. This snake’s range extends from eastern Southern California to New Mexico and south into the Sonoran and Chihuahuan deserts; this species is not known to live in Los Angeles or San Diego cities, in the Southern parts of Los Angeles County, or the coastal regions. 6 Southern Pacific rattlesnake venom contains other neurotoxins, including small basic peptides or beta-defensins, which are myotoxins. We report 7 cases of envenomation by the Southern Pacific rattlesnake that manifested clinical findings consistent with neurotoxicity. The first 6 cases were in the Los Angeles region, and the seventh case occurred in the San Diego region. Table summarizes these cases. CASE REPORT 1 A 60-year-old man with a history of hypertension who routinely uses aspirin, lisinopril, and amlodipine presented to the emergency department following a rattlesnake bite to the right leg while hiking. He described a 2-foot-long black snake and identified the snake as a Southern Pacific rattlesnake based on photographs. He developed pain at the site immediately. Approximately 1 hour later, he initially developed numbness in the right leg, and then progressed throughout the body. His initial examination was notable for 2 puncture wounds on the right anterior leg with some localized edema as well as truncal and gait ataxia. There was no ptosis. Motor strength and reflexes were normal. The sensation was intact to light touch. His initial laboratory studies were Volume -, no. - : - 2022 Annals of Emergency Medicine 1 TOXICOLOGY/CASE REPORT