Itsy Bitsy Spider Bites - ED Diagnosis and Management

A 34 year-old male with no medical problems presents to the emergency department with a bug bite. He states he was cleaning out his attic when he felt a pinch on his right arm. He saw a spider on his leg, killed it, and brought it in for you to see. Other than some mild redness and swelling around the bite, the patient has no complaints.

What kind of spider is this and how can you tell?

This is a black widow, which belong to the group of Lactrodectus spiders. Lactrodectus spiders are characterized by a red or orange hourglass marking on the abdomen. Females are larger than males, and only their bite can pierce through human skin.

What does the bite look like?

Bites from a black widow can start as a small, erythematous macule and grow into a larger targetoid lesion.

spiderbite

Is this bite venomous? (Hint: Yes, it is) How does the venom work?

alphatox

Black widows create a venom called Alpha-Iatrotoxin. Alpha-Iatrotoxin stimulates calcium channels in presynaptic cells causing the release of neurotransmitters like acetylcholine and norepinephrine.

What kind of symptoms should we expect to see?

Muscle cramps and spasms, rarely rigidity; can be generalized
Pain that starts local and can spread; usually only lasts for a day but can be severe
Diaphoresis near bite site
Hypertension, tachycardia
Headache, nausea, vomiting

What treatment can we offer in the ED for latrodectism?

Clean the wound with normal saline or sterile water
Control pain/spasm with opioids and benzodiazepines
IV calcium has been suggested to help alleviate symptoms, but there are no studies to support its use
Give ANTIVENOM! Different antivenoms are created for the different species of Latrodectus. Antivenom is usually very effective at relieving symptoms and shortens the course of disease. There are reports of anaphylactic reactions to antivenom, so be sure to monitor your patient after administration.

What would your disposition be for a patient with a black widow bite?

Usually, patients with black widow bites can be discharged home if adequately pain-controlled. If symptoms are severe, patients should be admitted for analgesia and observation.

References:
Schneir, Aaron B. “Chapter 205. Bites and Stings.” Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7e. Eds. Judith E. Tintinalli, et al. New York, NY: McGraw-Hill, 2011.

Black widows create a venom called Alpha-Iatrotoxin. Alpha-Iatrotoxin stimulates calcium channels in presynaptic cells causing release of neurotransmitters like acetylcholine and norepinephrine. [/expand]

What kind of symptoms should we expect to see?

Muscle cramps and spasms, rarely rigidity; can be generalized
Pain that starts local and can spread; usually only lasts for a day but can be severe
Diaphoresis near bite site
Hypertension, tachycardia
Headache, nausea, vomiting

What treatment can we offer in the ED for latrodectism?

Clean the wound with normal saline or sterile water
Control pain/spasm with opioids and benzodiazepines respectively
IV calcium has been suggested to help alleviate symptoms but there are no studies to support its use
Give ANTIVENOM! Different antivenoms are created for different species of Latrodectus. Antivenom is usually very effective at relieving symptoms and shortens the course of disease. There are reports of anaphylactic reactions to antivenom, so be sure to monitor your patient after administration.

What would your disposition be for a patient with a black widow bite?

Usually, patients with black widow bites can be discharged home if adequately pain-controlled. If symptoms are severe, patients should be admitted for analgesia and observation.