Crotalus oreganus concolor (Viperidae; Crotalinae): A case of envenomation with venom analysis from the envenomating snake and a diagnostic conundrum of myo-neurological symptoms

Abstract

Background:Crotalus oreganus concolor is a smaller species of North American rattlesnake indigenous to a confined middle region of the western United States. Reports of envenomation to humans are quite rare, and studies regarding the toxicity and pharmacological actions of C. o. concolor venom have shown the presence of low molecular weight myotoxins with myotoxic effects, and low metalloproteinase activity.

Method: A case that occurred in a remote location following the bite of a captive C. o. concolor is presented.

Case: The bite was sustained to the right thumb while removing the snake from a drawer-type housing unit and it resulted in a single fang puncture. Immediately, there was tingling in the bitten thumb followed by extreme tingling in the lips that progressed to the toes, and tightening of the face, forehead, and chest. Ambulance ground transport to a medical helicopter airlift site was initiated. While in transport early on the patient experienced a cascade of symptoms beginning with blurry vision, total body paresthesia, dyspnea and transient diaphragmatic paralysis followed by three waves of spastic muscle paresis of the hands and feet. These symptoms were transient and had resolved spontaneously prior to arrival at the hospital three hours post bite. Patient laboratory values and coagulation parameters remained within normal limits, except for a mild increase in D-dimer, elevated creatine kinase, and reduced total calcium. Local envenomation at the bite site was minimal, but numbness of the thumb persisted for longer than a week. For various reasons antivenom was not administered at any stage and symptoms were successfully managed symptomatically. At 24 hours, and following discharge, the patient was experiencing total body weakness, but able to walk slowly without assistance. He continued to experience myalgias in the right arm and overall generalized weakness for several days. Several weeks later sloughing of skin around the bite site was observed, but other local symptoms, other than numbness of the thumb, had resolved completely. Venom from the offending snake was collected and venom analysis performed revealing the presence of very high levels of myotoxins, small peptides that induce rapid tetanic muscle contractions in mice, and several serine proteinases often associated with coagulopathies.

Discussion/Conclusion: Causes of the patient’s transient myo-neurological symptoms were confounding diagnostically with respect to those that were potentially venom-induced versus those that may have been stress-induced physiological responses.