Called SCRATCH, the letters form a memorable acronym for symmetry, cluster, Rover, age, target/time, confused, household. It is a guide to the symptoms and features that help pediatricians and others to recognize the source of a rash.
Insect-bite skin rashes mimic the symptoms of a variety of conditions, ranging from fungal infections, scabies, allergies and environmental contacts, to HIV-associated dermatoses. Reactions to a bite are often delayed, making it difficult to trace exposure.
"SCRATCH could spare many children and their parents from going through invasive --not to mention expensive -- procedures if pediatricians recognize the problem early on," says Raquel Hernandez, M.D., a third-year resident at the Children's Center and lead author of the article, published in the July online edition of Pediatrics.
Hernandez and co-author Bernard Cohen, M.D., head of dermatology at the Children's Center, developed SCRATCH by examining a month's worth of patient records from visits to the Children's Center dermatology clinic. They found that the majority of children who were eventually diagnosed with an insect-bite rash had undergone extensive lab tests and skin biopsies before they were referred to Johns Hopkins.
The most common misdiagnosis was scabies, a skin infection caused by a parasite that produces red, itchy lesions. Many of the children were treated repeatedly for scabies.
If the rash fits this SCRATCH criteria, it's likely bug-borne, Cohen suggests:
S for Symmetry
Erruptions are usually symmetric and appear on exposed parts of the body, such as face, neck, arms, legs. Younger children may have rashes on their scalps. Diaper areas, palms and soles are not affected. The trunk is rarely affected. By contrast, scabies causes rashes on palms, soles and between toes and fingers.
C for Clusters
Lesions appear in "meal clusters," described as breakfast, lunch and dinner. The linear or triangular clusters are typical of bedbug bites, but also appear in bites caused by fleas.
R for Rover Not Required
Presence of pets in the household is not a criterion for diagnosis because a bite might occur outside of the home.
A for Age Specific
The condition is most prevalent in children between the ages of 2 and 10.
T for Target Lesions and Time
Target-shaped lesions -- named so for their resemblance to the bull's eye on a target -- 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. Most children develop full immunity by age 10 and no longer have recurrent rashes.
C for Confusion
Parents often express confusion and disbelief at the suggestion that there might be fleas or bedbugs in their homes. "One of the primary criteria is that if the parents don't believe me, I am probably right," Cohen says.
H for 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.
"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 said.