Urticaria

Papular urticaria is a common and often annoying disorder manifested by chronic or recurrent papules caused by a hypersensitivity reaction to the bites of mosquitoes, fleas, bedbugs, and other insects. Individual papules may surround a wheal and display a central punctum.
Although the overall incidence rate is unknown, papular urticaria tends to be evident during spring and summer months.
This eruption is primarily self-limited, and children eventually outgrow this disease, probably through desensitization after multiple arthropod exposures. However, adults can be affected, but at a much lower rate.

Etiology 
Papular urticaria is generally regarded to be the result of a hypersensitivity to bites from insects,such as mosquitoes, gnats, fleas, mites,bedbugs, caterpillars, and moths. However, it is unusual to identify an actual culprit in any given patient.One specific mite causing it is Peymotes ventricosus.
It is also known as the “grain itch”, “barley itch”, “straw itch”, “hay itch” and “mattress itch”.

Histology
The histopathologic pattern in papular urticaria consists of mild subepidermal edema, extravasation of erythrocytes, interstitial eosinophils, and exocytosis of lymphocytes.

Immunology
Immunohistochemical evidence suggest that a type I hypersensitivity reaction plays a central role in the pathogenesis of papular urticaria. The reaction is thought to be caused by a hematogenously disseminated antigen deposited by an arthropod bite in a patient who is sensitive. This theory is supported by the fact that these lesions can and often do occur in areas away from the bites. The putative antigen is unknown.

Clinical features
The eruption is characterized by crops of symmetrically distributed pruritic papules and papulovesicles. The lesions can also appear in an area localized to the site of insect bites, but they occur on any body part. The lesions tend to be grouped on exposed areas, particularly the extensor surfaces of the extremities. Scratching may produce erosions and ulcerations. Secondary impetigo or pyoderma is common.

Treatment
Its treatment is conservative and is symptomatic in most cases. Mild topical steroids and systemic antihistamines for relief of the itching. When severe enough use of short-term systemic corticosteroids is warranted. If secondary impetigo occurs, topical or systemic antibiotics may be needed.

Prevention
Use of insect repellents while the patient is outside and the use of flea and tick control on indoor pets are required when these individuals are being treated for papular urticaria.
Rigorous use of an effective insecticide may prevent insect bites and, accordingly, papular urticaria. Insecticides containing diethyltoluamide (DEET) are among the most beneficial.