Large Skin Reaction to Insect Bites and Stings: Is it Dangerous and What to Do?

Author: V. Dimov, M.D., Fellow, Creighton University Division of Allergy & Immunology
Reviewer: S. Randhawa, M.D., Fellow, LSU (Shreveport) Department of Allergy & Immunology
Faculty Adviser: A. Bewtra, M.B.B.S., M.D., Associate Professor, Creighton University Division of Allergy & Immunology

A 55-year-old male followed by the clinic for allergic rhinitis and asthma called the allergist on call with complaints of 5 recent insect bites/stings. He was working on his house (in August) when he was bitten by 5 insects: 4 of them slightly larger than flies and one which looked like a bee. He was bitten 5 hours ago, and now has edema and pain in the following areas: L cheek halfway to the jaw, left thumb, left little finger, right shin, and left hip, about 3 inches in size. He reports no SOB, wheezing, dizziness or fever. He did not see any stings left in the affected areas.

The patient put ice packs on the swellings and wants to know if anything else should be done.


A yellow jacket wasp with a typical narrow waist (left) and a honey bee with a fat hairy "fuzzy" body (right). Image source: Wikipedia 1, 2, GNU Free Documentation License.

PMH:
Allergic rhinitis, skin prick test positive for molds and grass, asthma, HTN

Medications:
Nasonex, Advair, Allegra, Amlodipine, triamcinolone lotion

What is the most likely diagnosis?
Local reactions to insect bites/stings

What is the strongest predictor of benign outcome of insect bites in this patient?
The long time frame. For example, most fatalities from wasp stings occur within an hour of the sting.

What advice would you give to this patient?
He had already taken an antihistamine (Allegra). He was advised to put triamcinolone lotion on the affected areas and to continue using the ice packs.

He reported large local reactions to bee stings several years ago but had no systemic symptoms at the time. The patient was asked to make an appointment for insect venom testing in 6 weeks.

Final diagnosis:
Local reactions to insect bites/stings

Summary

Skin testing

Skin testing in insect venom anaphylaxis is done 6 weeks after the sting.

Suggested indications for skin test with insect venom allergens:
- history of systemic reaction
- a local reaction away from the place of the sting ("a satellite")
- very large local reaction
- history of multiple stings on several occasions in the past

How to do skin testing in insect venom allergy - prick or intradermal?
Venom testing is performed initially with prick tests. If results are negative, intradermal testing is used with a concentration in the range of 0.001 to 0.01 µg/mL.

Skin test may be negative during the first 6 weeks after a sting due to a refractory period or "anergy."

Skin tests and RAST are complementary, as neither test alone will detect all patients with insect sting allergy.

Local Reactions

Large local reactions occur in 17-56% of stung people. The localized reaction may last 12-24 hours.

Large local reactions to stings have a 4-10% chance of a future systemic reaction. Local reactions may be life threatening if local swelling at the sting site compromises the airway. Edema may extend to 10 cm from site of the sting.

Topical antihistamines should not be used because they may penetrate the wounded skin, bind to proteins and cause sensitization through haptenization.


Mind map of insect venom allergy.

Systemic Reactions

In one study, 1-2% of the people experienced a generalized reaction, and 5% sought medical care. 3% of adults and less than 1% of children have systemic reactions to wasp stings. Adults are at a higher risk because they are more likely to have developed sensitization from a prior wasp sting.

Children generally have a more benign course after insect stings because they usually have only cutaneous systemic reactions. Remember:

C
Children
Cutaneous only

A
Adults
Airway
Anaphylaxis

Wasps and bees cause 30-120 deaths yearly in the United States.

Systemic reactions to stings are rapid: 50% of deaths occur within 30 minutes of the sting, and 75% occur within 4 hours.

In wasp stings, most deaths occur within 1 hour, with most severe reactions occurring within 10 minutes of the wasp sting. The systemic reaction is more related to the pre-existing level of circulating IgE rather than to the number of wasp stings.

Epinephrine, systemic steroids and ER care should be considered early in patients with systemic symptoms.

Acute management of anaphylaxis

Drugs: EASI

Epinephrine IM
Antihistamines PO, IM
Steroids PO, IM, IV
Inhaled b2-agonists, if wheezing; IV fluids if hypotensive


Mind map diagram of anaphylaxis.

All patients with history of systemic reaction to insect stings should be prescribed EpiPen Twin Pack.

EpiPen delivers epinephrine within seconds to minutes and "buys" the victim 20 minutes to get to the nearest emergency room. EpiPens expire every 18 months and it is recommended to have 2 of them handy.

References:
Insect Bites. Dirk M Elston. eMedicine.
Bee and Hymenoptera Stings. Hemant H Vankawala, Randy Park. eMedicine.
Wasp Stings. Carl A Mealie. eMedicine.
Anaphylactic Shock Due to Bee Sting
Venom Allergy: A Short Review.
Clinical review: ABC of allergies, Venom allergy. Pamela W Ewan. BMJ 1998;316:1365-1368.
Insect sting anaphylaxis. David B.K. Golden. Immunol Allergy Clin North Am. 2007 May; 27(2): 261–vii.
Hymenoptera Venom Allergy. Velma Paschall. Cleveland Clinic.
Insect Stings. NEJM, Volume 331:523-527, August 25, 1994.
Insect Stings and Bites. Ask the Expert. AAAAI.
Insect Sting. Ask the Expert. AAAAI.
Insect Sensitivity. Ask the Expert. AAAAI.
Insect Bite. Ask the Expert. AAAAI.

Published: 08/25/2008
Updated: 08/26/2008