Rosen & Barkin's 5-Minute Emergency Medicine Consult (660 page)

BASICS

• Syndromes caused by envenomation by black widow spider bite
  
• Mechanism of toxicity:
  
  • Females are responsible for human envenomations
    
  • Venom contains potent neurotoxin, α-latrotoxin:
    
    • Causes cation-channel opening presynaptically, resulting in increased neurotransmitter release into synapses and neuromuscular junctions
      
    • Increased neurotransmitter release causes increased neurologic, motor, and autonomic effects
      
• Morbidity and mortality are dose dependent
  
• Severity of envenomation depends on:
  
  • Premorbid health of victim:
    
    • HTN or cardiovascular disease increase risk
      
  • Size and age of victim:
    
    • Children (i.e., smaller size for a given dose of venom) are at greater risk of morbidity and mortality.
      
  • Number of bites
    
  • Location of bite wounds
    
  • Size and condition of spider
    
• Rarely fatal
  

Black widow spider features:

• Appearance:
  
  • Glossy black with red markings shaped like an hourglass or a pair of spots on the ventral aspect of the globular abdomen
    
  • Females have 25–50 mm leg spans and 15 mm long bodies
    
• Found throughout North America, except the far north and Alaska
  
• Prefer dark sheltered hideaways such as garages, barns, outhouses, woodpiles, and low-lying foliage
  
• Most bites occur during the warmer months when spiders are defending their webs and egg clutches
  

DIAGNOSIS

• History of spider bite very unreliable and species usually not identified
  
• Bite:
  
  • Described as a pinprick or pinch, if felt at all
    
• Local complaints (within minutes of bite):
  
  • Pain:
    
    • Sharp, burning at the bite site
      
    • Usually resolves spontaneously within minutes or hours
      
    • May become worse and spread proximally from the bite
      
• Systemic complaints (within 15–60 min):
  
  • Cardiac:
    
    • Palpitations
      
    • Chest pain or tightness
      
  • Pulmonary:
    
    • Shortness of breath
      
    • Cough
      
  • Neuromuscular:
    
    • Headache
      
    • Dizziness
      
    • Painful regional muscle cramps and spasms
      
    • Cramping may progress to larger muscle groups
      
    • Arm bites may lead to arm and chest muscle tightness and dyspnea
      
    • Leg bites may lead to abdominal pain and leg spasms
      
    • Cutaneous dysesthesias and hyperesthesias
      
    • Localized or diffuse diaphoresis
      
  • GI:
    
    • Nausea, vomiting
      
    • Abdominal pain
      
  • Genitourinary:
    
    • Painful persistent erection
      
  • Gynecologic:
    
    • Pregnant patients may develop uterine contractions and preterm labor
      
  • Skin:
    
    • Pruritus
      
  • Psychiatric:
    
    • Anxiety
      
    • Sense of impending doom
      

• Vital signs may be abnormal:
  
  • HTN or hypotension
    
  • Tachycardia or bradycardia
    
  • Fever
    
  • Tachypnea
    
• Cardiac:
  
  • Dysrhythmias
    
  • Myocarditis
    
• Pulmonary:
  
  • Bronchorrhea
    
  • Pulmonary edema
    
  • Respiratory failure:
    
    • Usually due to respiratory muscle weakness
      
• Abdomen:
  
  • Rigidity
    
• Genitourinary:
  
  • Priapism
    
• Neurologic findings:
  
  • Tetanic contractions, fasciculations or tremors of extremities
    
  • Spasm and rigidity in large muscle groups
    
  • Autonomic instability
    
  • Seizure
    
• Skin:
  
  • Local:
    
    • 2 pinpricks from the spider’s fangs
      
    • Tender and blanched skin with surrounding erythema (“target lesion”)
      
    • Swelling
      
    • Localized sweating
      
  • Diffuse:
    
    • Urticaria
      
    • Piloerection
      
    • Generalized diaphoresis
      
• Psychiatric:
  
  • Acute toxic psychosis
    
  • Agitation or restlessness
    

Diagnosis is based on:

• Clinical presentation
  
• Careful inquiry to elicit spider bite history
  
• Identification of spider (if possible)
  

• No specific blood tests for black widow spider venom
  
• CBC:
  
  • WBC may be mildly elevated
    
• Electrolytes, calcium
  
• BUN, creatinine
  
• Lipase, LFTs
  
• Creatine kinase:
  
  • Elevated in patients with significant muscle spasm
    
• Cardiac enzymes
  
• Pregnancy test
  
• Urinalysis:
  
  • May demonstrate albuminuria
    
• ABGs in rare cases with pulmonary edema
  
• ECG and cardiac monitoring for:
  
  • Patients with known cardiac disease
    
  • Patients with chest pain, unstable vital signs or dysrhythmias
    
  • May show digitalis effect transiently
    

• CXR for respiratory complaints
  
• Abdominal imaging to rule out other causes of pain
  

• Acute surgical abdomen (e.g., appendicitis, cholecystitis, pancreatitis, AAA)
  
• Ureterolithiasis/nephrolithiasis
  
• Sympathomimetics (e.g., cocaine, amphetamines)
  
• Hypocalcemia
  
• Tetanus
  
• Muscular injury or strain
  
• Hypertensive emergency
  
• MI/acute coronary syndrome
  
• Anxiety disorder
  
• Allergic reaction
  

TREATMENT

• ABCs/ACLS
  
• Immobilize the wound site and apply cool compresses or ice for comfort during transport to hospital
  
• Supportive measures (analgesics, anxiolytics) may be required for patients with systemic symptoms
  
• Negative-pressure venom extraction devices have not been recommended for widow spider bites
  
• Every effort should be made by caregivers at the scene to find and bring in the responsible spider for identification
  

• ABCs
  
• ACLS as needed
  
• Fetal monitoring for pregnant patients
  

• Clean the bite site thoroughly
  
• Tetanus prophylaxis
  
• Antiemetics for nausea and vomiting
  
• Analgesics
  
• Antihistamines
  
• Benzodiazepines for agitation and restlessness
  
• Muscle cramps/spasm therapy:
  
  • Benzodiazepines
    
  • Narcotics
    
• Antihypertensive agents for symptomatic HTN
  
• Antivenin:
  
  • Elicit history of allergy to horse or horse serum
    
  • Indications:
    
    • Moderate to severe symptoms that do not respond to symptomatic measures
      
    • Significant HTN
      
    • Respiratory distress
      
    • Symptomatic and pregnant
      
    • Priapism
      
    • Severe rhabdomyolysis
      
    • Compartment syndrome
      
    • Seizures
      
• Perform a skin test for sensitivity to horse serum prior to antivenin administration (test kit included in the antivenin package)
  
• Watch for type I immediate hypersensitivity reaction in the 1st 20 min:
  
  • Occurs in up to 25% of recipients
    
  • Consider pretreatment with antihistamines or SC epinephrine 1:1,000
    
  • Treat anaphylactic reactions with steroids, antihistamines, epinephrine, and cardiopulmonary support
    
  • Due to the small quantity of antivenin used, if serum sickness reactions occur, they are usually mild
    
  • Effectiveness is usually apparent within 2 hr of the 1st treatment and repeated doses are rarely necessary
    
  • Antivenin may help prevent persistent neuropathic symptoms
    

• Antivenin: 1 ampule (2.5 mL) diluted into 50–100 mL of D
  ₅
  W or NS (peds: Same dose) IV over 1 hr
  
• Diphenhydramine: 10–50 mg IV or IM q6–8h (peds: 5 mg/kg/d div. QID)
  
• Lorazepam: 1–2 mg IV or IM (peds 0.01 mg/kg IV or IM)
  
• Morphine sulfate: 2–10 mg (peds: 0.1 mg/kg) IV or IM PRN (titrate to patient response)
  
• Sodium nitroprusside: 0.5–10 mcg/kg/min if diastolic >120 mm Hg
  
• Tetanus prophylaxis
  

FOLLOW-UP