Papular Urticaria

Papular urticaria is a chronic or recurrent hypersensitivity reaction to bites of fleas, bedbugs, mosquitoes, mites or other arthropods, chiefly in children aged 2 to 10 years. It reflects delayed type reaction to antigens in the insect saliva.

• Younger children are most affected before they develop desensitisation.
• Pets, bedding, soft furnishings and outdoor exposure are the sources.
• Often affects several family members simultaneously, though only susceptible individuals react.

Groups of intensely itchy, erythematous urticarial papules, 3 to 10 mm, with a central punctum, sometimes vesicles or bullae, in crops on exposed limbs, trunk and buttocks.

• Recurrent episodes in summer and rainy seasons; scratching leads to excoriation and crusting.
• Differential diagnosis: scabies, chickenpox, impetigo, insect bite, folliculitis, atopic dermatitis, Gianotti Crosti syndrome, dermatitis herpetiformis, Langerhans cell histiocytosis, prurigo.
• Complications: secondary infection, impetigo, post inflammatory pigmentation, scarring, sleep disturbance, school absence, anxiety.

Clinical, with an exposure history to pets, bedding and environment.

• Skin scraping to exclude scabies; swab if infected.
• Inspect pets, bedding and furniture for fleas, bedbugs and mites.
• Biopsy and allergy tests are rarely needed.

Remove the source and relieve itch.

• Supportive: wash bedding and clothing at 60 degrees Celsius weekly, vacuum carpets, treat pets for fleas with veterinary approved products, treat the home with insecticide where infestation is confirmed, use insecticide treated bed nets, wear long sleeves, keep nails short, cool baths.
• Pharmacological: hydrocortisone 1 percent or mometasone furoate 0.1 percent cream once or twice daily for 5 to 7 days; calamine lotion; oral cetirizine (2 to 5 years 2.5 mg twice daily, 6 to 11 years 5 mg daily, 12 years and over 10 mg daily); topical fusidic acid 2 percent cream three times daily for 7 days, or oral flucloxacillin 25 mg/kg/day in four divided doses for 7 days, for secondary infection. Repellent: DEET 10 to 30 percent (children over 2 months) or picaridin 20 percent.
• Procedures: none.
• Special groups: pregnancy, emollient, mild topical steroid and cetirizine acceptable; infants, avoid DEET under 2 months and avoid sedating antihistamines; atopic children, treat the underlying eczema.
• Red flags: widespread vesicles with fever, secondary infection with cellulitis, burrows in finger webs (scabies), lesions not responding, anaphylaxis or angioedema.
• Follow-up: review at 2 weeks; reinforce environmental control, as the condition usually settles in 2 to 3 years with desensitisation.