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Educational Objectives:

After evaluating this article, participants will be able to:
1. Incorporate strategies into clinical practice for the identification of black widow envenomations
2. Provide appropriate management for black widow envenomations
3. Anticipate the expected complications from black widow envenomations

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Case History

The patient is a 51-year-old male who presents to the ED with a complaint of severe abdominal pain and cramping of 8 hours duration associated with diaphoresis, low-grade fevers, and anorexia. According to the patient, his symptoms began approximately 1 hour after suffering a scrotal bite from “some insect” while trying on a pair of boxer shorts his wife had just given him for Valentine’s Day.
 

The patient is normally healthy, is on no daily medications, has no previous abdominal surgeries, and no kidney stones. He drinks socially, but denies any drugs of abuse.

Physical Exam

Gen: Middle aged male in severe pain distress, rocking side to side in fetal position
Vitals:  P=120/min; RR=40/min; T=100.4 F; BP= 150/90 mmHg
Lungs: Clear to auscultation CV: RRR S1S2 no murmurs
GI: Severe diffuse abdominal tenderness with rebound and guarding, normoactive bowel sounds, no organomegaly
Rectal: (-) Heme G/U: Normal external genitalia with swelling & erythema of scrotum, normal descended testis
Ext: Diaphoretic, good pulses, normal color, no rash
Neuro: No focal deficits, motor/sensory intact

Laboratory Data

CBC: WBC= 19.4  H/H= 45/15 PLT= 313K
Lytes:  Na= 140  K=4.0  Cl= 110 HCO3= 23
BUN/Cr: 15/0.9   Glucose= 150
Lipase: 20 LFTs: Normal range
KUB/CXR:  Nonspecific bowel gas pattern, no free air
U/A:  0 WBCs  0 RBCs

Clinical Course

The spouse brings in a dark-colored spider to the ED with a distinctive “red hourglass” configuration on its lower body segment, which she discovered and subsequently “crushed” in her husband’s Valentine’s Day boxer shorts.

Black Widow Spiders – Anatomy

The Latrodoctus genus is a common spider found in temperate and tropical ones of the world. The species most common in North America include Latrodoctus bishopi, L. geometricus, L. Hesperus, L. variolus, and L. mactans. Black widows seem to be more prevalent during warmer periods of the year. Females can be up to 20 times larger in size, darker in color, and more toxic than their male counterparts. Black widows are described as charcoal or black with eight eyes, eight legs, fangs, and poison glands, and a characteristic red hourglass mark on the ventral aspect of the abdomen. To propagate the species, female black widows have been known to devour their male counterpart after mating as a food source, since the males often die soon after copulation leaving the female to rear the egg sac.

Pathophysiology

The female black widow is generally considered poisonous to humans; whereas the males are not due to their small jaws and a minimal number of poison glands. Black widows spiders control the amount of venom they inject; an estimated 15% of bites to humans are nonenvenomating.  The venom’s toxicity is due to the alpha-latrotoxin present in the spider’s venom. This toxin facilitates exocytosis of synaptic vesicles and the release of the neurotransmitters norepinephrine, gamma-aminobutyric acid, and acetylcholine. The toxin also causes degeneration of motor endplates, resulting in denervation. The venom destabilizes nerve cell membranes by opening ion channels, causing a massive influx of calcium into the cell, which may lead to hypocalcemia.

Clinical Presentation

Black widow bites can produce a pinprick sensation but often go unnoticed. Within the first two hours after the bite, the site may develop redness, cyanosis, urticaria, or a characteristic halo-shaped target lesion. These local symptoms may be followed by generalized symptoms of pain in regional lymph nodes, chest, abdomen, and lower back. Pain classically descends down the lower extremities with burning sensation on the soles of the feet. Abdominal rigidity and vomiting can be quite severe and may even be mistaken as a surgical emergency. According to one study, signs and symptoms in children were erythema on wound areas, irritability, constant crying, sialorrea, agitation, and seizures. Adult patients often describe pain on the wound site, thoraco-abdominal pain, muscle spasms and fine tremors.

Flexor spasm of the limbs can cause the patient to assume a fetal position while writhing in pain. Other severe symptoms include hypertension, sweating, salivation, dyspnea with increased bronchosecretions, and convulsions. If untreated, these symptoms may persist for up to several days, followed by muscle weakness and pain for several weeks. Less common effects include compartment syndrome of the upper extremity and priapism. Death is uncommon, although it may occur from respiratory or cardiac failure, with an overall mortality of <5%.

Management

Local wound care is appropriate and pain at the bite site may be relieved with early application of ice. Tetanus prophylaxis should be updated, but antibiotics are unnecessary unless there is evidence of a secondary wound infection. Oral analgesics may be of benefit if the pain is severe, although parenteral analgesics, such as morphine, may be used if the pain is generalized. Muscle spasms may require oral or parenteral benzodiazepines. In the past, administration of calcium gluconate was considered because of possible hypocalcemia following black widow envenomation. This is currently not advocated as recent studies have proven no benefit to the administration of calcium.

In extreme cases with severe symptoms, antivenom (Antivenin Latrodectus mactans) is recommended.  The antivenom is available in Australia and Arizona where envenomations occur more frequently, although current supplies are limited nationally.  Since antivenom is derived from horse serum, the patient may be skin tested by injecting a 1:10 dilution subcutaneously to test for an anaphylactic reaction prior to administration of a full dose of the antivenom. Although this practice is commonly recommended, in reality, the antivenom has been associated with a relatively low rate of allergic reactions. The use of latrodectus-specific antivenom is restricted to patients with severe envenomation and no allergic contraindications, and in whom opioids and benzodiazepines are ineffective. Young children and elderly patients with severe toxicity should receive antivenom early in the clinical course, as well as patients with hypertensive and cardiac disease. Patients receiving antivenom may experience flu-like symptoms or serum sickness 1-3 weeks following treatment. This entity is generally self-limited and responsive to antihistamines and prednisolone.

Disposition

Any symptomatic patient who has suffered a bite from a black widow spider can be admitted for observation and pain control. If there is cardiopulmonary compromise or convulsions, the patient is admitted to the intensive care unit for stabilization and possible antivenom administration.

Clinical Outcome

Therapeutically, the patient is given calcium gluconate and morphine without pain relief. Before the patient is rushed to the OR for an exploratory lap, he is given black widow spider antivenom with adequate pain resolution. He recovers without sequelae apart from a chronic case of arachnophobia. Since the husband had recently obtained a substantial life insurance policy and will leaving all his worldly possessions to his wife, she is fully questioned by authorities but no “foul play” is ultimately suspected.

REFERENCES
  • Clark RF: The safety and efficacy of antivenin Latrodectus mactans.  Clin Tox 39:125-127, 2001.
  • Clark RF, Wethern-Kestner S, Vance MV, Gerkin R: Clinical presentation and treatment of black widow spider envenomation: A review of 163 cases. Ann Emerg Med 21:782-787, 1992.
  • Offerman SR, Daubert GP, Clark RF: The treatment of black widow spider envenomation with antivenin latrodectus mactans: a case series. Perm J. 2011 15(3):76-81, 2011.
  • Cohen J, Bush S: Case report: compartment syndrome after a suspected black widow spider bite. Ann Emerg Med. 45(4):414-6, 2005.
  • Erickson T, King R: Spider and Arthropod Bites, in *Pediatric Emergency Medicine: A Comprehensive Study Guide, Strange, Ahrens, Schafermeyer (eds). McGraw-Hill, New York, 43rd Edition: 2009.
  • Rash LD, Hodgson WC: Pharmacology and biochemistry of spider venoms. Toxicon 40:225-254, 2002.
  • Saucier JR: Arachnid envenomation. Emerg Med Clin North Am. 22(2):405-22, 2004.
  • Shlamovitz GZ: Man with back pain. Black widow spider bite. Ann Emerg Med 50(5): 496, 2011`
  • Tong T, Scheir A, Clark RF: Arthropod Bites and Stings. In: Pediatric Toxicology: Diagnosis and Management of the Poisoned Child. Erickson T, Ahrens W, Aks S, et al (eds): McGraw-Hill, New York, 1st ed, 2005 pp 556-566.


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