Children afflicted with insect-bite rashes are often
misdiagnosed or referred for extensive and costly tests,
but a new, easy-to-remember set of guidelines developed at
Hopkins Children's Center should help.
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," said Raquel Hernandez, 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, associate
professor in the School of Medicine and 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
"These guidelines are really intended to make
pediatricians consider insect-bite hypersensitivity as a
diagnosis and think twice before referring a child for a
skin biopsy or another invasive procedure," Cohen said.
Using the tool is straightforward, Cohen said. If the
rash fits the SCRATCH criteria, it's likely bug-borne. The
seven checkpoints are:
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
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
A for age specific. The
condition is most prevalent in children between the ages of
2 and 10.
T for target lesions and for
time. Target-shaped lesions — so named 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
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 said.
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
"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