A 30-year-old woman, who was otherwise healthy with no known medical history, presented to the emergency department with new onset of right-sided chest pain that began while she was sleeping. When she awoke, she saw something crawling down her chest and onto the bed. She grabbed it and placed it in a plastic bag to bring to the ED with her.
What bit her, and what are the treatment options?
Find the diagnosis and case discussion on p. 27.
Diagnosis: Black Widow Spider Envenomation
Latrodectus species, also known as black widow spiders, are found across the United States. The female can cause serious envenomation, though no fatalities have been reported in the past 50 years.
The spider's body size is 1-2 cm, and it is usually a shiny black color with a red hourglass shape on the ventral abdomen. Black widow venom contains alpha-latrotoxin, which causes the opening of nonspecific cation channels, leading to increases in calcium influx, release of acetylcholine at the motor endplate, and levels of norepinephrine. This appears to be designed to induce rapid paralysis of the insect's victim. (Lancet 2011;378:2039.)
The clinical presentation includes mild local skin findings at the bite site that range from mild erythema to a target lesion with a central punctate site, central blanching, and an outer erythematous ring. The target lesion may be accompanied by localized diaphoresis and piloerection. The bite site typically becomes painful within 30 minutes to two hours.
Painful muscle cramping and fasciculations begin near the bite site over the next three to four hours and progress centripetally toward the large muscle groups of the chest, abdomen, and back. The severity of these muscle spasms can produce board-like rigidity, weakness, dyspnea, headache, and paresthesias. The clinical picture may mimic an acute surgical abdomen, acute myocardial infarction, aortic dissection, and obstructive ureterolithiasis. Other common symptoms include hypertension, tachycardia, nausea, and vomiting. Fever and leukocytosis may also be seen. (Ann Emerg Med 1992;21:782.)
The diagnosis of black widow spider envenomation is based on clinical presentation. No specific diagnostic test for envenomation exists, but an ECG, basic metabolic panel, complete blood count, troponin, and urinalysis may be helpful in evaluating for other causes when the diagnosis is unclear.
The initial management of a patient with black widow spider envenomation consists of symptomatic and supportive care. The bite site should be appropriately cleaned and tetanus prophylaxis provided if the patient's immunizations are not up-to-date. Treatment for pain and muscle spasms typically begins with opioids and benzodiazepines. IV calcium, dantrolene, and methocarbamol were previously studied and are not effective for pain relief and muscle cramping compared with a combination of benzodiazepines and opioids and are not recommended.
Antivenom may also be considered in cases where the pain and cramping is not relieved by analgesia, particularly in patients under a year old or over 65. Black widow antivenom is effective and resolves all symptoms quickly, but it does carry a risk of causing hypersensitivity and allergic reactions including anaphylaxis. It is contraindicated in those with hypersensitivity to horse serum (the antivenom is equine-derived), a significant reactive airway disease, or a history of atopy. The typical dose is one vial of antivenom IV infused over 15 to 30 minutes. The dose is the same for children and adults. (Curr Pharm Biotechnol 2012;13:1935.)
This patient was initially treated with oral analgesics, but 30 minutes after arrival, she began experiencing severe worsening pain to her chest and back. She received multiple rounds of IV pain medications without improvement, and the decision was made to give her the Latrodectus antivenom. Her symptoms completely resolved within 20 minutes after receiving the antivenom, and she was discharged home with no residual pain and no complications from the antivenom administration.