Papular Urticaria
Photoclinic
A 7-year-old boy was brought for evaluation of an intensely pruritic rash that recurred every May and lasted through September. The lesions affected the arms and legs primarily, were bilaterally distributed, and worsened after mosquito bites. The child had been treated symptomatically with oral antihistamines, antibiotics, and corticosteroids.
Numerous erythematous, hyperpigmented, 0.5- to 1-cm macules and papules were noted on the child’s lower legs and arms. Multiple excoriations were also apparent. The trunk and other areas normally covered by clothing were spared. Physical findings were otherwise normal.
Papular urticaria—also called insect bite–induced hypersensitivity—accounts for about 5% of pruritic rashes in children.1 This recurrent pruritic eruption is thought to be a reaction to the bites from insects. Mosquitoes are among the most commonly implicated insects. The rash occurs during warmer months, when insects are active, and is typically confined to the bite areas.
The diagnosis of papular urticaria is clinical and can be based on the recently proposed SCRATCH principles2:
S – symmetric distribution.
C – crops or clusters of differing appearance.
R – lack of a pet or “Rover.”
A – age-specific (2 to 10 years old).
T – target appearance and prolonged time to resolution (usually weeks to months).
C – confused pediatrician or parent.
H – household with only a single member affected.
This child’s presentation met all 7 criteria and had 2 other common characteristics: “exposed skin only” and “seasonal exacerbation.” These features added to the principles as E and S makes “SCRATCHES,” which may be a more specific acronym.
Treatment strategies focus on avoiding insect bites (with protective clothing, netting, and insect sprays). Repeated scratching of bites often leads to hyperpigmentation and excoriation which, rarely, leads to secondary bacterial infection. Topical corticosteroids can be applied to individual lesions and may reduce inflammatory changes; however, skin thinning and hypopigmentation may result with prolonged use. Oral antihistamines lessen pruritus, but prophylactic use of these agents has not been studied.
Although some children can become desensitized from repeated arthropod exposures, symptoms can persist into adulthood.
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.