Background: In the late nineties, Bond and Burkhardt described a severe thrombocytopenic phenomenon from envenomation by Crotalus horridus. This thrombocytopenia persisted despite administration of platelets and antivenom. Questions remain regarding the clinical significance and time to resolution of this thrombocytopenia. In addition, as new antivenoms are available in North America, the response to current treatment is not well reported. The purpose of this study is to provide further insight into the approach to treatment of Crotalus horridus envenomation. Methods: This is a retrospective chart review of 21 cases of presumed envenomation by C. horridus. Data collected included age, sex, antivenom administration, laboratory data, length of hospital stay, blood products adminis-tered, and general clinical course. We also evaluated platelet response to antivenom, bleeding outcomes, and complications from envenomation.Results: Patients' ages ranged from 19 to 71 years. All patients were men. Most patients presented with thrombocytopenia and all had limb swelling. Patients responded initially to antivenom treatment, however subsequently developed a profound thrombocytopenia, including fourteen with platelet counts less than 20 x 10 (Tu, 1991)/L. Abnormalities in thromboelastography (TEG) were noted in conjunction with thrombocytopenia. Patients displayed persistent thrombocytopenia despite administration of Crotalidae polyvalent immune Fab or Crotalidae immune F(ab')2. Median time to rebound platelet count greater than 20 x 109/L was ten days (range 6-12 days) from envenomation. Complications included a partial finger amputation in one patient, bleeding gums in four patients, bloody stools in two patients, bloody nasogastric output in one patient. No patients required red blood cell transfusion and no deaths occurred. Conclusion: Practitioners treating C. horridus should recognize the possibility of severe thrombocytopenia and its persistence despite antivenom. They should counsel patients on appropriate abstention from activities that could lead to trauma, as well as the importance of follow up for repeat laboratory studies to ensure the resolution of thrombocytopenia.
