Urticaria multiforme represents a morphologic subset of urticarial reactions. It is a common, benign hypersensitivity reaction mediated by histamine that predominantly affects children between 4 months and 4 years of age. This entity often manifests after a preceding illness, medication exposure, or vaccination. It can be mistaken for more concerning entities, namely erythema multiforme or serum sickness.
Reported culprit medications include furazolidone, amoxicillin, palivizumab, albuterol, topiramate, nitrofurantoin, aspirin, pyrazolone, and mesalamine / 6-mercaptopurine / omeprazole, and reported vaccines include those against varicella, rotavirus, Haemophilus influenza, diphtheria, tetanus, and pertussis.
On physical exam, patients appear nontoxic and systemic findings are typically limited to a low-grade fever. Cutaneous findings include large polycyclic, annular, erythematous wheals on the face, trunk, and extremities. The wheals may develop an ecchymotic or dusky center. Although the dusky appearance can be concerning for erythema multiforme, there are no true target lesions, blistering, or necrosis of the skin and/or mucous membranes. The lesions are often pruritic but not painful. Individual lesions typically do not last longer than 24 hours.
Other key associated findings include dermatographism, acral and facial angioedema without associated laryngoedema, and symptoms of a preceding or concomitant illness such as low-grade fever, cough, or diarrhea.
The cutaneous eruption is self-limited and lasts about 1-2 weeks without any intervention. The lesions heal without post-inflammatory hyperpigmentation or scarring.
ICD10CM: L50.9 – Urticaria, unspecified
SNOMEDCT: 126485001 – Urticaria
Differential Diagnosis & Pitfalls
Serum sickness-like reaction – This entity is on the same spectrum as urticaria multiforme, but individual lesions may last longer than 24 hours. Acral rash, fever, lymphadenopathy, and myalgias after drug exposure are more prominent features of this disease entity compared with urticaria multiforme. Dermatographism is less prominent compared with urticaria multiforme. Unlike serum sickness, true arthritis, hypocomplementemia, and immune complexes are absent.
Serum sickness – Rare allergic reaction with cutaneous eruptions, true arthralgias, renal involvement, and potentially neurologic involvement, with hypocomplementemia and immune complexes.
Erythema multiforme – Individual lesions last longer than 24 hours. Morphologic features include a classic target appearance, with a dusky center surrounded by pale rim followed by erythematous rim. There may also be blistering or necrosis of the skin and mucous membranes.
Urticarial vasculitis – Urticarial wheals with a dusky or purpuric appearance that last longer than 24 hours. Histopathology demonstrates evidence of cutaneous leukocytoclastic vasculitis. This entity is often associated with an underlying systemic disorder.
Viral exanthem – Nonspecific viral exanthems tend to be more macular and papular with a diffuse distribution.
Kawasaki disease – Look for mucocutaneous changes such as fissured lips and/or a strawberry tongue, acral edema and erythema, as well as high fever, conjunctivitis with perilimbal sparing, and cervical lymphadenopathy.
Juvenile rheumatoid arthritis – Evanescent macules or slightly elevated papules that may have a serpiginous or irregular border, along with fevers and joint pain of greater than 6 weeks' duration in a child younger than 16 years of age.
Drug Reaction Data
Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.