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A 4-year-old boy with multiple edematous, pruritic red papules on the arms and legs
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A 4-year-old boy presents to your office complaining of several red lesions on his arms and legs associated with severe pruritus for the past several days. He has a 2-year history of similar lesions developing mainly in the summertime, which resolve within a week and leave behind hyperpigmentation.
Occasionally, one or two lesions will expand rapidly for 24 to 48 hours, become more tense and painful, and feel slightly warm to palpation, leading to treatment with oral antibiotics for presumed cellulitis. He does not have a history of fevers associated with the skin lesions. Despite similar outdoor exposure, other family members deny developing similar lesions.
Marissa J. Perman
Can you spot the rash?
Diagnosis: Insect bite hypersensitivity to mosquitoes
Case discussion
Insect bite hypersensitivity describes a particular response to insect bites often found in young children but may affect patients of any age. In most cases, there tend to be multiple sites with a central punctum or small papule, often set close together and similar in appearance. Because of the intense erythema, edema and occasional complaint of pain rather than pruritus, these lesions can sometimes be mistaken for cellulitis and improperly treated with antibiotics.
Insect bite hypersensitivity is seen much more commonly in the summer when the mosquito burden is higher, but the reaction can occur year round if a patient is exposed. Many types of insect bites can lead to insect bite hypersensitivity, including fleas and bed bugs, as the individual’s skin creates a similar reaction to multiple species. This article will focus mainly on mosquito bite hypersensitivity.
Allergenic proteins in the saliva of the mosquito lead to the local skin reaction observed in most people. Upon first exposure to a mosquito bite, no reaction occurs. Subsequent bites lead to an immune-mediated response. This typically consists of a wheal occurring within 20 to 30 minutes after the bite (immediate reaction) followed by a more persistent, pruritic, erythematous wheal occurring 24 to 36 hours after the bite (delayed reaction) that may last several days then resolves. These reactions are immunoglobulin E, IgG and T-cell mediated. Desensitization occurs with time but may take several years as patients begin to avoid exposure to mosquitoes by wearing protective clothing and using insect repellant.
Large local reactions (usually greater than 3 cm) also follow an immediate or delayed pattern, and the delayed response may persist for several weeks. If the inflammation in the skin is intense or severe edema results, vesicles or bullae may develop. Large local reactions associated with fever have been coined “Skeeter syndrome” and generally occur in otherwise healthy children. In these cases, the area becomes warm, edematous and red, leading to confusion with cellulitis but occurs shortly after a mosquito bite, helping to differentiate it from an infectious process.
Numerous, variably sized, erythematous,
edematous, excoriated papules and plaques
on the legs.
Photo courtesy of Perman MJ
The differential diagnosis includes cellulitis (usually hot, painful, lack of central punctum or crust and almost always individual rather than multiple sites), eosinophilic cellulitis, also known as Wells’ syndrome (an intense reddish-blue edematous plaque sometimes in response to an insect bite with abundant eosinophils and flame figures on histopathology), pityriasis lichenoides and lymphomatoid papulosis. Most of these other conditions can be distinguished by history, thorough physical examination paying close attention to distribution and biopsy, if needed.
Avoidance is the key to preventing insect bite hypersensitivity to mosquitoes. Removal of standing water around the home and limiting outdoor activity at times of high mosquito activity (dawn and dusk) is recommended. Clothing that covers skin provides excellent protection when feasible. In addition, insect repellant is also useful, particularly products that contain N,N-Diethyl-meta-toluamide (DEET) in concentrations between 10% and 30%. DEET is recommended by the AAP for children aged at least 2 months. DEET and permethrin 0.5% can be applied to clothing. Other recommended insect repellants include picaridin, IR3535 (3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester), or the plant-based oil of lemon eucalyptus and its synthetic equivalent p-Menthane-3,8-diol. Citronella and other botanicals found at specialty stores may also confer some protection but are less effective. Mosquito nets and magnets are other options.
Treatment of symptoms may provide relief once bites occur, including moderate potency topical steroids and H1 antihistamines. It is important to be aware of children with hypersensitivity reactions to insect bites, particularly mosquitoes, to provide a diagnosis, appropriate management and education on further prevention.
References:
AAP. Red Book Online: Prevention of Mosquitoborne infections: Available at: aapred
book.aappublications.org/content/1/SEC70/SEC128.body?sid=6bb8627a-aa78-4a5a-b7a5-3d8e25cea37b. Accessed Aug. 31, 2013.
Crisp HC. Ann Allergy Asthma Immunol. 2013;110:65-69.
Kulthanan K. J Dermatol. 2010;37:1025-1031.
Simons FE. J Allergy Clin Immunol. 1999;104:705-707.
For more information:
Marissa J. Perman, MD, is an attending physician at The Children’s Hospital of Philadelphia. She can be reached at permanm@email.chop.edu.
Disclosure: Perman reports no relevant financial disclosures.