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Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1997. Updated by Dr Oakley and Dr Karen Koch, Consultant Dermatologist, WITS Donald Gordon Mediclinic, Johannesburg, South Africa. March 2018.
Papular urticaria is a common reaction to insect and arachnid bites. It is more common in children than in adults . It presents during the summer or autumn months as crops of very itchy red papules and vesicles.
Despite the name, papular urticaria is not true urticaria, which is characterised by temporary wealing that resolves within hours. Weals in papular urticaria last for days to weeks. Papular urticaria is not associated with an internal complaint.
It is also called a persistent insect bite reaction.
Papular urticaria most often occurs in children. This is because desensitisation to insect bites has not yet developed .
It may also occur in adults, especially in travellers to new environments.
Papular urticaria is thought to be an immunological reaction to insect bites. The reaction dies down after a few months or years, as the person becomes desensitised to them. The initial bite is rarely noticed.
Fleas and mites that live on cats and dogs are most often responsible .
Not everyone with papular urticaria has pets, and it can be nearly impossible to work out what a patient is reacting to. There have been reports of allergy to mosquitoes, gnats, bird mites, carpet beetles, caterpillars and other insects .
Papular urticaria presents with very itchy clusters of red bumps.
Scratching papular urticaria causes the spots to become crusted.
The spots remain for a few days to a few weeks and can leave persistent hyperpigmented marks (postinflammatory pigmentation) or hypopigmented scars, especially if they have been scratched deeply.
Papular urticaria is not dangerous.
The differential diagnosis of papular urticaria includes:
Papular urticaria is usually a clinical diagnosis. A biopsy may support the diagnosis, as insect bites have a characteristic microscopic appearance.
The histopathology of papular urticaria includes mild dermal oedema, extravasation of erythrocytes, interstitial eosinophils, and exocytosis of lymphocytes. Vasculitic features may be noted.
Seek veterinary advice regarding management of the infested animal(s).
Papular urticaria is normally self-limiting. The immunological basis of this reaction means that it may take months or even years for children to become desensitised to the offending insect . Papular urticaria may clear up on holiday or on moving house.
Occasionally the eruption can clear for years and then recur unexpectedly.
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