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BALTIMORE, June 29 — A simple set of guidelines with the acronym SCRATCH can help nail down a diagnosis of a bedbug or flea bite bite, or dermatitis, or something else.

"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," said Bernard Cohen, M.D., director of pediatric dermatology at the Johns Hopkins Children's Center here.

Dr. Cohen and Raquel Hernandez, M.D., developed the guidelines and the mnemonic acronym SCRATCH, which stands for Symmetry, Cluster, Rover, Age, Target/time, Confused, Household, they reported in the July 1 and early online editions of Pediatrics.

They developed the guidelines after reviewing a month's worth of charts, and found that a majority of children with a final diagnosis of an insect-bite hypersensitivity reaction had undergone extensive lab tests and skin biopsies before they were referred to Johns Hopkins.

"Healthy itchy children provide a diagnostic and therapeutic challenge to parents, pediatricians, and pediatric dermatologists," the authors wrote. "The complaint of itch may prompt a costly, exhaustive, and invasive evaluation. In our pediatric dermatology practice, insect bite-induced hypersensitivity reactions, known as papular urticaria, account for 5% of these patients."

Papular urticaria can be caused by the bites of bedbugs, fleas, or mosquitoes, or the stings of bees or wasps. It's characterized by chronic or recurrent eruptions of intensely pruritic papules, vesicles, and wheals caused by a hypersensitivity reaction.

The lesions most commonly occur in linear clusters on exposed skin, but not in the genital, perianal, or axillary regions, the authors explained.

The intense itching caused by the eruptions often leads to scratching that results in excoriations that in turn can lead to infections, scarring, and permanent changes in skin pigmentation (either hyper- or hypopigmentation), particularly in dark-skinned people.

"We found that this common clinical entity is frequently not included in the differential diagnosis for pruritic pediatric rashes, suggesting that this may be an unfamiliar and elusive diagnosis for referring primary care providers and dermatologists alike," Dr. Hernandez and Dr. Cohen wrote.

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

Among the conditions that papular urticaria can be mistaken for are scabies, atopic dermatitis, contact dermatitis, and pityriasis lichenoides.

To help their colleagues make an early, accurate diagnosis or to rule out the possibility of flea or bedbug bites, the authors proposed the mnemonic acronym SCRATCH. The elements include:

• Symmetry — Most patients with insect-bite hypersensitivity reactions present with symmetrical eruptions on the face, neck, arms, and legs, with sparing of the diaper area, palms, and soles of the feet.
• Clusters — "Lesions usually appear in a 'meal cluster,' sometimes described as 'breakfast, lunch, and dinner,'" the authors noted. "These linear or triangular groupings of lesions are characteristic of bedbug bites; however, they may also be seen in flea bites."
• Rover Not Required — The diagnosis is not dependent on the presence of household pets. Exposure could come from periodic visits to a relative's house, for example.
• Age-specific — The condition is most prevalent in children between the ages of two and 10.
• Target Lesions/Time — Bull's-eye-rashes are typical of insect-bite reactions. "Time" refers to the chronic nature of the eruption and the need for patience and watchful waiting. Parents are advised to prevent secondary infections with appropriate use of nail and hand hygiene and moisturizers.
• Confusion — Parents are confused by the conflicting information they have been given, and the referring practitioner may find it hard to accept the diagnosis of an admittedly confusing condition. "We came to realize that the sheer implication that there might be bedbugs or fleas in the home was quite an insult (not to mention a disappointing diagnosis after being told that there are few remedies besides observation)," the authors wrote.
• Household — Unlike scabies or dermatitis, insect-bite reactions may affect only household members who are hypersensitive, and could be confined to a single person.

"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," Dr. Hernandez said.

Treatment, they wrote "is usually disappointing to families and practitioners alike. Fortunately, however, this condition is rarely serious and always improves with time. We emphasize the three 'P's' of management — prevention, pruritus control, and patience."

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