3-year-old boy presents to the ED with diffuse itchy rash
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A 3-year old boy presented to the ED for evaluation of an itchy rash. One week before presentation, he had complained of ear pain and was prescribed amoxicillin by his pediatrician for otitis media. A week later, he developed rhinorrhea, cough and a pruritic rash. The rash started on his hands and feet, then spread to his trunk and extremities. Some lesions seemed to disappear within a few hours. His hands and feet became swollen, and he developed pain with ambulation, prompting the ED visit for evaluation.
Can you spot the rash?
A. Erythema multiforme
B. Serum sickness-like reaction
C. Urticaria multiforme
D. Viral exanthem
Case Discussion
Urticaria is a type 1 hypersensitivity reaction characterized by erythematous, pruritic swellings in the skin and subcutaneous tissue (Figures 1 and 2). The lesions are usually the result of immunoglobulin E-mediated mast cell activation and release of vasoactive mediators including histamine, prostaglandins and leukotrienes. Urticaria is classified into two categories based upon duration of the eruption: acute and chronic urticaria. Acute urticaria is characterized by an eruption lasting less than 6 weeks and is the most common type of urticaria in children. Most of these cases in children are due to an infection, which is most often viral. These patients will typically report antecedent symptoms of upper respiratory infection or otitis media before the onset of the rash. Medications also can elicit acute urticaria, most commonly penicillin antibiotics. Chronic urticaria is defined as urticaria lasting more than 6 weeks and is more commonly seen in adults.
Individual lesions of urticaria classically present as a “wheal and flare,” with a central edematous swelling and surrounding erythema. By definition, individual lesions are transient and resolve within 24 hours. Itching is the most common symptom. Many infants and young children can experience angioedema in the face, hands and feet. Significant swelling in the feet or around joints can lead to difficulty walking. When urticarial lesions coalesce, they can form large annular (ringlike) and polycyclic configurations. They may also develop a hemorrhagic dusky center and resemble targets, which can be confused with erythema multiforme (EM). Thus, urticaria forming annular patterns has been coined urticaria multiforme (UM) — (correct choice, C) — and is a common presentation of urticaria in infants and young children. The differential diagnosis of acute annular urticarial lesions also includes serum sickness-like reactions (SSLRs), which are most frequently associated with antibiotics such as cefaclor. SSLR and UM are likely on the same spectrum and are thus treated similarly.
There are many clinical clues that can be used to differentiate UM from EM. Unlike the fleeting lesions of UM that resolve within 24 hours, EM is composed of lesions that are fixed and can last for weeks. Although UM lesions can sometimes form dusky centers and resemble the targetoid lesions of EM, they do not become bullous or necrotic. Another finding unique to UM is the presence of dermatographism, which is the ability to elicit a wheal after scratching the skin. Fevers, lymphadenopathy and arthralgias may be present in both UM and SSLR.
First-line treatment for acute urticaria is with nonsedating H1 antihistamines such as cetirizine, loratadine or fexofenadine. A second agent is often needed, and an H2 blocker such as ranitidine or famotidine is given concomitantly with an H1 blocker. It is important to continue the antihistamines after clearance and gradually taper them off to prevent recurrence. Any potential offending medications should be discontinued. It is also crucial to avoid nonsteroidal anti-inflammatory drugs (which often are erroneously given to control pain from acral edema or treat fevers) because they can cause mast cell degranulation and worsening of urticaria. Systemic steroids are generally not indicated, especially when an underlying infection is suspected as the trigger for the urticaria. Steroids are typically reserved for severe cases that are recalcitrant to antihistamines. Overall, UM is generally responsive to antihistamines and the rash tends to resolve within days to weeks for most patients.
- References:
- Shah KN, et al. Pediatrics. 2007;doi:10.1542/peds.2006-1553.
- Chapter 20. The hypersensitivity syndromes. In: Paller A, Mancini AJ, eds. Hurwitz Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood and Adolescence. 5th ed. Edinburgh: Elsevier; 2016: 467-494.
- For more information:
- Michele Khurana, MD, is a pediatric dermatology fellow at The Children’s Hospital of Philadelphia. She can be reached at khuranam@email.chop.edu.
- Marissa J. Perman, MD, is an attending physician at The Children’s Hospital of Philadelphia.
Disclosures: Khurana and Perman report no relevant financial disclosures.
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