Issue: August 2006
August 01, 2006
4 min read

Spot the Rash

Issue: August 2006
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This child presented to the doctor’s office with recurrent itchy red edematous papules with central vesicles. Note that the lesions are linear in nature, with a “breakfast, lunch, dinner” presentation. The child lives in a suburban neighborhood in the northeastern United States and has been treated with 1% topical hydrocortisone. What is your diagnosis?


This child had papular urticaria.

Pediatric patients are often misdiagnosed or referred to undergo extensive and costly tests when it comes to diagnosis of these insect bite-hypersensitivity reactions. However, a new set of guidelines could help aid in clinical diagnosis and potentially reduce unnecessary testing and treatment procedures.

Figure 2
Image of papular urticaria resulting from an insect bite. The linear organization of these lesions is known as “breakfast, lunch and dinner”, typical of fleabite hypersensitivity reactions.

SCRATCH, short for symmetry, cluster, Rover, age, target/time, confused, household, is a guide to the symptoms and features that can help pediatricians to recognize the source of a rash. Insect bite-induced hypersensitivity reactions account for a significant number of referrals to the pediatric dermatology clinic at the Johns Hopkins Children’s Center, according to a study appearing in an online edition of Pediatrics. These rashes mimic the symptoms of a variety of conditions, ranging from fungal infections, scabies, allergies, dermatitis and environmental contacts, to HIV-associated dermatosis. Reactions to a bite are often delayed, making it difficult to trace exposure.

Diagnosticians Raquel Hernandez, MD, a first year general pediatrics fellow at the Children’s Center and one of the study’s researchers and colleague Bernard Cohen, MD, head of dermatology at the Children’s Center, developed SCRATCH by examining patient records from visits to the dermatology clinic. They found that 5% of office visits to the dermatology clinic over a four-week period were attributed to papular urticaria or insect bite reactions. Case reports also showed that most of these children had undergone extensive lab tests and skin biopsies before they were referred to the clinic. Scabies was the most common misdiagnosis and many of the children were treated repeatedly for scabies.

After reviewing four pediatric case reports from December 2003 to January 2004, Hernandez and Cohen found that insect bite-induced hypersensitivity is frequently not included in the differential diagnosis for pruritic pediatric rashes. Furthermore, the terminology for insect bite reactions can be confusing, according to the study.

“We found that identification of insect bite-induced hypersensitivity in children is difficult because of the variability of symptoms,” Hernandez and Cohen wrote in the study. “We have proposed the SCRATCH principles as a means to help the practitioner with the diagnosis.”

Figure 3
Image of papular urticaria resulting from an insect bite. The child developed recurrent episodes of multiple itchy papules with central blisters that healed with hyperpigmentation. The lesions were most prominent on exposed areas of the skin, particularly the legs.

Using the tool is straightforward. If the rash fits the SCRATCH criteria, it’s likely bug-borne.

  • Symmetry – Eruptions are usually symmetric and appear on exposed parts of the body, such as the face, neck, arms and legs. Younger children may have rashes on their scalps. Diaper areas, palms and soles are not affected and the trunk is rarely affected. By contrast, scabies causes rashes on palms, soles and between toes and fingers. Careful inspection may show bites along the sockline and waistline or other clothing pressure sites.
  • Clusters – Lesions typically appear in linear or triangular clusters described as “meal clusters”. They are typical of bedbug bites, but also appear in fleabites. They initially appear as itchy, red edematous, indurated, urticarial pustules, which develop a central vesicle within one to three days.
  • Rover not required – Presence of pets in the household is not a criterion for diagnosis because a bite might occur outside of the home or in areas where there is no history of a pet in the environment. Exposures to mosquitoes and bedbugs are other important components to consider when conducting a patient’s history, according to the study.
  • Age specific – The condition is most prevalent in children between 2 and 10 years. Most children develop full immunity by age 10 and no longer have recurrent rashes.
  • Target lesions and time – Target-shaped lesions are typical of insect bite hypersensitivity. Time indicates the chronic/recurrent nature of the eruptions. Many patients may have delayed reactions and may not experience flare-ups until months or years after the initial exposure.
  • Confusion – Parents often express confusion and disbelief at the suggestion that there might be fleas or bedbugs in their homes.
  • Household with single family member affected – Unlike conditions that have similar symptoms, such as scabies and atopic dermatitis, insect bite rashes often appear in a single member in a family. Because this condition is caused by hypersensitivity, some individuals will react and others will not.

“Common sense might tell us that fleas and mosquitoes would affect other members of the family, but we must keep in mind that these rashes develop in children who have hypersensitivity that others do not have,” Hernandez stated in a release.

Three “P’s” of therapy

“Treatment of IBIH [insect bite-induced hypersensitivity] is usually disappointing to families and practitioners alike,” Cohen and Hernandez wrote in the study. “Fortunately, however, this condition is rarely serious and always improves with time.”

Hernandez and Cohen suggested management include the basic principals of prevention, pruritis control and patience.

Prevention includes wearing protective clothing outdoors and using insect repellent. Pet owners should implement flea-control measures such as flea collars, medication, frequent bathing of pets and wash bedding in hot water. If the source is bedbugs, continue to persist, families should consider professional application of pesticide treatments to remove allergens, according to the study.

For pruritus control, high potency topical steroids can help with individual lesions, they suggested. Antihistamines may provide some systemic relief, however there is little evidence that supports widespread use of these medications in children with recurrent and chronic lesions.

Pediatricians should also advise parents to be patient. Physicians should advise them of the possible recurrent nature of insect bite-induced hypersensitivity and reassure them of the eventual development of tolerance of symptoms and resolve of symptoms.

These three management tools of therapy “should be discussed with patients and parents to prevent unnecessary laboratory studies and multiple consultations,” they advised.

“Early diagnosis allows for appropriate patient and family counseling resulting in averting use of expensive, unnecessary laboratory studies and avoidance of painful procedures,” they wrote.

For more information:
  • Hernandez RG, Cohen BA. Insect bite-induced hypersensitivity and the SCRATCH principals: A new approach to papular urticaria. Pediatrics. 2006;118:e183-e190.

Spot the Rash is a monthly case study featured in Infectious Diseases in Children designed to test your skills in pediatric dermatology issues.