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DESCRIPTION
Spiders of the genus Latrodectus include the following:
- L. mactans, the black widow, is found in the United States, South Africa, and South America.
- L. hesperus includes the brown widow, red widow, and other spiders, which are found in the United States.
- L. hasseltii is the red-back spider of Australia and New Zealand.
- L. tredecimguttatus is native to the Mediterranean, Eastern Europe, and Russia.
- L. indistinctus is the button spider of South Africa.
TOXIC DOSE
One bite is toxic.
PATHOPHYSIOLOGY
The venom acts at neuromuscular junctions to cause the release of acetylcholine and norepinephrine at postganglionic sympathetic synaptic sites. This produces uncontrolled muscle contraction.
EPIDEMIOLOGY
- Although poisoning is common, the toxic effects are typically mild to moderate; death is a rare event.
- Extremes of age and underlying cardiopulmonary disease increase the risk of death.
RISK FACTORS
Envenomation is usually an accidental incident and occurs through activities that place the victim in the spider habitat (e.g., putting hands in woodpiles and dark corners, harvesting grain by hand, or using an outhouse).
PREGNANCY AND LACTATION
Monitor pregnant patients for premature labor or spontaneous abortion; however, outcome is typically good.
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DIFFERENTIAL DIAGNOSIS
Nontoxicologic causes of pain and cramping often accompanied by sweating include acute abdomen, myocardial infarction, or sickle cell crisis.
SIGNS AND SYMPTOMS
- Localized pain and cramping "migrating" from large muscle groups in the bitten extremity, to buttocks, abdomen, or chest over 30 to 120 minutes strongly suggests the diagnosis.
- Effects peak in the first few hours but may persist for days.
Vital Signs
Hypertension and tachycardia are common, but rarely require treatment.
HEENT
Although ptosis and eyelid edema may occur, these reactions are uncommon.
Dermatologic
- Diaphoresis is common.
- The bite site may show two small punctures with a small erythematous and diaphoretic area.
Cardiovascular
- Dysrhythmias and myocardial ischemia occur rarely.
- A bite to the arm or chest may produce pain that mimics myocardial ischemia.
Pulmonary
- Tachypnea and respiratory distress may develop.
- Respiratory failure has been reported but is rare.
Gastrointestinal
- Nausea and vomiting are common. Abdominal pain predominates.
- Boardlike rigidity of abdominal muscles may mimic acute abdomen.
Musculoskeletal
- Pain and spasm of large muscle groups develop within 30 minutes to 2 hours and resolve over 24 to 48 hours.
- Mild rhabdomyolysis has been reported.
Neurologic
- Weakness, hyperreflexia, headache, anxiety, and paresthesia are common and may persist for several days.
- Children may be irritable or drowsy.
Reproductive
- While there is concern that uterine muscle spasm could induce miscarriage or labor, pregnant women have had successful outcomes.
- Pregnant patients should be monitored for premature labor or spontaneous abortion.
PROCEDURES AND LABORATORY TESTS
Essential Tests
No tests may be needed in mildly symptomatic patients.
Recommended Tests
- ECG should be performed in patients with hypertension or chest pain. Effects of a bite to the arm may migrate to the chest, simulating myocardial ischemia.
- Creatine kinase is measured in patients with prolonged muscle spasm to rule out rhabdomyolysis.
- Arterial blood gas is used in patients with respiratory distress.
- Other tests may be needed to rule out acute abdomen (e.g., complete blood count, electrolytes, abdominal radiography, and computed tomography).
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Treatment should be focused on ensuring adequate ventilation and controlling muscle spasm and pain.
DIRECTING PATIENT COURSE
The health-care professional should call the poison control center when:
- Severe hypertension, myocardial ischemia, respiratory failure, intractable pain, or other severe effects are present.
- Signs and symptoms are not consistent with widow spider envenomation.
- Administration of antivenom is planned.
- Drug interaction or underlying disease presents an unusual problem.
The patient should be referred to a health-care facility when:
- The patient or caregiver seems unreliable.
- Toxic effects develop.
- Toxicity is not consistent with widow spider envenomation.
- An underlying disease presents an unusual problem.
Admission Considerations
Inpatient management is warranted in symptomatic pregnant patients or patients with persistent pain, respiratory distress, severe hypertension, or myocardial ischemia despite therapy.
ANTIDOTES
Black widow spider antivenom (Lactrodectus mactans) is available from Merck.
- Indications
- The primary indication is severe envenomation (marked hypertension, respiratory distress, myocardial ischemia, persistent pain despite parenteral opioids and muscle relaxants, or evidence of labor or miscarriage).
- Antivenom should be considered in patients with underlying cardiopulmonary disease.
- Contraindications include hypersensitivity to horse serum.
- Administration
- Antivenom should be administered in a monitored critical care setting, with preparation to manage the airway and treat anaphylaxis.
- The skin test involves injection of 0.02 ml of test solution (included with the antivenom) intradermally and observation for a wheal-and-flare reaction. A negative skin test does not rule out the possibility of a hypersensitivity reaction to antivenom.
- Antivenom is administered as one vial diluted in 50 to 100 ml of 0.9% saline administered intravenously over 20 to 30 minutes. Alternatively, one vial may be injected intramuscularly as described in the package insert.
- Adverse effects
- Acute allergic reactions, including anaphylaxis, may develop.
- Serum sickness (e.g., fever, rash, and myalgia) may occasionally develop 5 to 14 days after administration.
ADJUNCTIVE TREATMENT
The aggressive use of parenteral opioids and muscle relaxants provides the most effective pain relief short of antivenom. Frequent small bolus doses should be administered while monitoring respiratory and cardiac function.
Analgesics
- Morphine sulfate. Adult dose is 2 to 5 mg intravenously every 15 to 60 minutes as needed; pediatric dose is 0.05 mg/kg to 0.1 mg/kg up to 5 mg every 15 to 60 minutes intravenously as needed.
- Meperidine. Adult dose is 25 to 50 mg intravenously every 30 minutes to 4 hours as needed to a maximum dose of 300 mg. Pediatric dose is 1 to 2 mg/kg up to 50 mg intravenously or intramuscularly every 30 minutes to 4 hours.
Muscle Relaxants
- Diazepam. Adult dose is 2 to 10 mg intravenously every 1 to 4 hours. Pediatric dose is 0.04 to 0.3 mg/kg up to 10 mg intravenously every 1 to 4 hours as needed.
- Methocarbamol. Adult dose is 15 mg/kg in-travenously over 5 minutes, followed by 15 mg/kg infusion over 4 hours. Pediatric dose is 15 mg/kg intravenously over 5 minutes every 6 hours.
Calcium Gluconate
- Calcium gluconate is used to relieve pain, although results are inconsistent. It is not as effective as opioids and muscle relaxants. Relapse of pain and cramping is common.
- Adult dose is 10 ml of 10% solution intravenously over 10 to 20 minutes, which may be repeated every 3 to 4 hours; pediatric dose is 50 mg/kg, up to 500 mg/kg/day.
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PATIENT MONITORING
- Respiratory and cardiac function should be monitored continuously during acute episode and during treatment.
- Patients who receive antivenom may develop serum sickness (e.g., fever, rash, and arthralgia) 5 to 14 days later.
EXPECTED COURSE AND PROGNOSIS
- Toxic effects typically peak within hours and then improve over several days.
- Muscle pain, malaise, and weakness may persist for several days to weeks.
- No permanent sequelae are expected.
DISCHARGE CRITERIA/INSTRUCTIONS
- From the emergency department
- The patient may be discharged after 4 to 6 hours if pain control is achieved and severe complications do not develop.
- The patient should be discharged with an oral narcotic analgesic and muscle relaxant.
- From the hospital. The patient may be discharged when pain resolves.
Section Outline:
ICD-9-CM 989.5Toxic effect of venom.
See Also: SECTION III, Black Widow Spider Antivenom chapter.
RECOMMENDED READING
Clark RF, Wethern-Kestner S, Vance MV, et al. Clinical presentation and treatment of black widow spider envenomation: a review of 163 cases. Ann Emerg Med 1992;21:782-787.
Moss HS, Binder LS. A retrospective review of black widow spider envenomation. Ann Emerg Med 1987;16:188-191.
Timms PK, Gibbons RB. Latrodectism—effects of the black widow spider bite. West J Med 1986;144:315-317.
Author: Katherine M. Hurlbut
Reviewer: Rivka S. Horowitz