Etiology
- Latrodectus Mactans (black widow spider, show-button spider)
- Seasonal Prevalence: most black widow bites occur between April-October in the United States
- Geography: found in USA and Canada (black widow is most abundant in southeastern United States)
- Spider resides in dark spaces wood piles, rock piles, sheds, garages, and basements
- Female (which bites humans) is black with 1 cm body, 5 cm legspan, and has red hourglass mark on ventral abdomen
- Spider is aggressive and bites on slight provocation (typically when trapped or web is disturbed)
- Latrodectus Bishopi (red-legged widow spider)
- Geography: found in Florida
- Other Latrodectus species
- Found in other temeperate and subtropical parts of the world
Physiology
- Alpha Latrotoxin (Neurotoxin) in Venom
- Lack of local necrosis
- Binds irreversibly to nerves and depletes acetylcholine and norepinephrine from presynaptic nerve terminals
- Clinical Effects
- Neuropathy -> acute hypoventilation
- Autonomic activation
- Diffuse central and peripheral nervous system excitation
Diagnosis
- CBC: leukocytosis
Clinical Manifestations
Widow Spider Bite Site
- Asymptomatic bite site: occurs in many cases
- Fang puncture sites at bite site: uncommon
- Momentary sharp pain at bite site: however, this is often not prominent on exam
Neuro Manifestations
- Anxiety
- Painful Muscle Cramps/Spasms of Extremities and Trunk: cramping pain begins within 15-60 min after bite
- Headache
- Hyperreflexia (see Hyperreflexia)
- Weakness
- Twitching/Tremor/Fasciculations (see Tremor)
- Parasthesias of Hands/Feet (see Peripheral Neuropathy)
- Intracerebral Hemorrhage
Cardiac Manifestations
- Tachycardia (see Sinus Tachycardia): due to autonomic activation
- Systolic Hypertension (see Hypertension): due to vasoconstriction
GI Manifestations
- Abdominal Pain with Rigidity (see Abdominal Pain): due to muscle spasms
- However, characteristically, abdomen is not tender on exam
- Nausea/Vomiting (see Nausea and Vomiting)
Pulmonary Manifestations
- Labored Respirations: due to respiratory muscle weakness
- Acute Hypoventilation/Respiratory Failure (see Acute Hypoventilation)
Renal Manifestations
- Urinary Retention
- Rhabdomyolysis (see Rhabdomyolysis)
- Acute Kidney Injury (AKI) (see Acute Kidney Injury)
Other Manifestations
- Salivation
- Diaphoresis/Sweating
- Fever (see Fever)
- Uterine Contractions/Pre-Term Labor
Treatment
Treatment of Pain at Bite Site
- Spontaneous Resolution: pain at bite site usualy subsides within several hours (although recurrence over the next 2-3 days are common)
- Analgesics: may be required
- Hot Bath: prompt, but temporary relief of pain
- RICE Therapy
- Rest
- Ice
- Compression
- Elevation
Treatment of Muscle Spasms
- Spontaneous Resolution: painful spasms begin to subside within the first 12 hrs (but may recur for days-weeksbefore fully resolving)
- Calcium Gluconate
- Administration: (10%-10 mL IV over 10-20 min)
- Clinical Efficacy: transient cessation of muscle cramps
- Benzodiazepines: useful for muscle spasms
- Methocarbamol (Robaxin) (see Methocarbamol)
- Administration: IV
- Clinical Efficacy: may relieve muscle spasms
Widow Spider Antivenom
- Administration: 1 vial in 50 mL of NS IV given over 15 min
- May need to test for hypersensitivity before use
- Effective with a few hrs -> may repeat PRN
- Clinical Efficacy
- Controversial: indicated mainly for uncontrolled hypertension, pregnancy, eizures, or respiratory arrest
- Side Effects
- Anaphylaxis (see Anaphylaxis)
- Serum Sickness (see Serum Sickness): as antivenom is derived from horse serum
Tetanus Prophylaxis
- Indicated
Prognosis
- Deaths: have been reported (mostly in children, elderly, and debilitated)
References
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