Bug-Bite Diagnosis: A Reminder for Dermatologists

[Pediatric Management]

Bug-Bite Diagnosis: A Reminder for Dermatologists

Before diagnosing skin infections, physicians must provide thorough examination. Experts provide an easy to remember system to approach insect bites.

By Ted Pigeon, Associate Editor

Insect bites and associated hypersensitivity reactions known as papular urticaria unfortunately go unnoticed by physicians sometimes. According to a new study in Pediatrics,1 children affected by such eruptions are often misdiagnosed and subjected to expensive, invasive, and ultimately unnecessary procedures. Therefore, clinicians may appreciate an easy-to-remember system researchers recently proposed to aid diagnosis of bug-bites.

Missed Diagnoses The exact pathophysiology of papular urticaria is still debated, but the reaction itself is defined by chronic or recurrent eruptions of pruritic papules, vesicles, and wheals resulting from a hypersensitivity reaction to biting insects. Lesions most commonly occur in linear clusters

Bed Bugs are Biting Back

Insect-bite-induced hypersensitivity (IBIH) can result from various antagonists, including cat and dog fleas and mosquitoes. The common bed bug is also known to produce an identical reaction despite being less commonly considered an offending agent. Thought to be mostly eradicated in the 1950s, bed bugs infestations have shown an enormous increase (500 percent) both in the US and Europe in the past three years.2,3 Unlike mosquitoes, bed bugs do not depend on surrounding environment for reproduction, therefore they can be transported to any climate and thrive. Heavily populated locations allow for the frequent transfer and proliferation of bedbugs in places like hotels and apartment buildings.2

on exposed skin and can cause intense itching, which can lead to infections, scarring, and permanent changes in pigmentation if patients irritate the lesions.

Bernard Cohen, MD and Raquel Hernandez, MD, authors of the recent Pediatrics study, say that papular urticaria account for a significant number of all referrals from pediatricians and dermatologists to their pediatric dermatology clinic at Johns Hopkins University. Papular urticaria can be mistaken for contact dermatitis, atopic dermatitis, pityriasis lichenoides, and scabies. Findings from the study highlight unique cases in which doctors often misdiagnose and should consider papular urticaria.

Start from Scratch Accurate, early diagnosis of these lesions is important, the authors write, allowing, "appropriate patient and family counseling resulting in averting use of expensive, unnecessary laboratory studies and avoidance of painful procedures." To aid diagnosis, the authors propose the mnemonic, "SCRATCH":

1. Symmetry: Most patients present with a symmetric eruption, say the authors. The most commonly affected areas tend to be exposed areas of the face, neck, arms, and legs, which contrasts with distribution found in scabies.

2. Clusters: Lesions usually appear in a triangular "meal cluster," which the authors say is sometimes described as "breakfast, lunch, and dinner," characteristic of bedbug bites (though sometimes seen in flea bites).

3. No "Rover" Necessary: The authors note that physicians find it difficult to diagnose papular urticaria when the patient has no history of a pet in the home. However, only a remote history of pet exposure is necessary to produce a rash; lack of "Rover" in the home should not eliminate IBIH from the differential.

4. Age: Authors stress that IBIH is most prevalent between the ages of two and 10, which may help physicians narrow the differential diagnoses.

5. Target Lesions/Time: According to the authors, Target lesions are characteristic for IBIH, especially in patients with dark skin pigments. "T" also stands for time, emphasizing the chronic nature of the eruption and the need for patience from the patient and the physicians.

6. Confusion: Parents may be confused by misinformation about infestations, leading them to reject the IBIH diagnosis and the physician to doubt him/herself. "We came to realize that the sheer implication that there might be bedbugs or fleas in the home was quite an insult," the authors write.

7. Household: IBIH often only affects a single family member, the authors note; it is actually quite rare for multiple family members to have similar symptoms of IBIH because individuals have different thresholds for sensitization.

1. Hernandez RG, Cohen BA. Insect Bite-Induced Hypersensitivity and the SCRATCH Principles: A New Approach to Papular Urticaria. Pediatrics. 2006 118: 1: 189- 196. 2. Hwang S, et al. Bed Bug infestations in an urban environment. Emerg Infect Dis. 2005; 11: 533- 538 3. Owen J. Bloodthirsty bedbugs stage comeback in US, Europe. National Geographic News. May 13, 2004 hhtp://news.news/2004/05/0513_040513_bedbugs.html.

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Practical Dermatology

August 2006

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