Spider Bite, Black Widow, Emergency Medicine

Basics

Description

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

Etiology

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

Signs and Symptoms

History

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

Physical Exam

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 spiders 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

Essential Workup

Diagnosis is based on:

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

Diagnosis Tests & Interpretation

Lab

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

Imaging

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

Differential Diagnosis

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

Pre-Hospital

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

Initial Stabilization/Therapy

ABCs
ACLS as needed
Fetal monitoring for pregnant patients

Ed Treatment/Procedures

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

Medication

Antivenin: 1 ampule (2.5 mL) diluted into 50 " 100 mL of D5W 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

Disposition

Admission Criteria

Pediatric, elderly, pregnant, or symptomatic patients
Significant cardiovascular symptoms and signs, or severe HTN, particularly in presence of premorbid cardiac disease or chronic HTN
Respiratory distress or pulmonary edema
Persistent symptoms not responding to aggressive management and specific antivenin

Discharge Criteria

Asymptomatic patients with no positive identification of a black widow spider can be released after observation for 1 " 2 hr
Asymptomatic patients with no comorbid illness with a positive identification of the black widow spider should be observed for a minimum of 4 " 6 hr and discharged if their condition does not change
All discharged patients must be instructed to watch for the following symptoms and to seek appropriate follow-up:
- Hematuria
- Rash
- Joint pain
- Lymphadenopathy
- Shortness of breath
- Signs of infection
Discharged patients who received antivenin should be instructed to watch for signs of serum sickness:
- Type III delayed hypersensitivity
- Uncommon
- Occurs 5 days " 3 wk post treatment
- Treat with antihistamines and steroids

Issues for Referral
Toxicology consult for patients requiring admission or antivenin administration

Follow-Up Recommendations

In most untreated patients, symptoms peak after 2 " 3 hr and then begin to resolve, occasionally recurring episodically over the following few days
In otherwise healthy adults, complete resolution of symptoms occurs within 2 " 3 days
Neurology follow-up if persistent neurologic symptoms last weeks to months including:
- Fatigue
- Generalized weakness or myalgias
- Paresthesias
- Headache
- Insomnia
- Impotence
- Polyneuritis

Pearls and Pitfalls

Widow bites in infants may present as intractable crying
A high fever and WBC count should prompt consideration of alternatives to spider bites (e.g., infection)

Additional Reading

Boyer LV, Binford GJ, McNally JT. Spider bites. In: Auerbach, ed. Wilderness Medicine. 5th ed. Philadelphia, PA: Mosby; 2007.
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(7):782 " 787.
Otten EJ. Venomous animal injuries. In: Marx JA, Hockenberger RS, Walls RM, et al., eds. Rosens Emergency Medicine. 7th ed. Philadelphia, PA: Mosby; 2009.
Weinstein S, Dart R, Staples A, et al. Envenomations: An overview of clinical toxinology for the primary care physician. Am Fam Physician. 2009;80(8):793 " 802.

Codes

ICD9

989.5 Toxic effect of venom

ICD10

T63.311A Toxic effect of venom of black widow spider, acc, init

SNOMED

217666004 Poisoning due to black widow spider venom (finding)

Home

Erectile Dysfunction

Doctor123.org