Papular urticaria is a common and often annoying disorder manifested by chronic or recurrent papules. Is there 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.
Papular urticaria, usually called hives, is characterized by large numbers of very itchy red bumps (papules) that come and go every few days over a period of a month or so. The bumps are usually between 0.2 and 2 cm. in size and some may develop into fluid-filled blisters (bullae). This condition is usually triggered by allergic reactions to insect bites, sensitivity to drugs, or other environmental causes. In some cases, swelling of the soft tissues of the face, neck, and hands (angioedema) may also occur.
Because it is difficult for children and adults to resist scratching these itchy crusted bumps, the possibility of infection is great and caution must be taken. Papular urticaria may accompany, or even be the first symptom of various viral infections including hepatitis, infectious mononucleosis, or German measles (rubella). Some acute reactions are unexplained, even when recurrent
Although the overall incidence rate is unknown, papular urticaria tends to be evident during spring and summer months; in some climates, such as that in San Francisco, California, this condition may affect children throughout the year. In addition, despite no known racial or sex predisposition, certain ethnic groups (specifically Asians) may be more predisposed to more intense reactions, and a small Nigerian study reported a slight female predominance for skin diseases such as papular urticaria and atopic dermatitis. Papular urticaria was evident in 2.24% of 5250 first-time pediatric patients, with 6029 diagnoses in one pediatric dermatology service survey. A survey of skin disorders in more than a 1000 new pediatric patients at a hospital in Bangalore, India found insect bite reactions and papular urticaria in 5.1% A Nigerian survey of 491 pediatric dermatoses in 441 patients found papular urticaria in 6.7% of them.
This eruption is primarily self-limited, and children eventually outgrow this disease, probably through desensitization after multiple arthropod exposures. However, adults can be affected, albeit at a much lower rate.
Etiology and Pathophysiology
The histopathologic pattern in papular urticaria consists of mild subepidermal edema, extravasation of erythrocytes, interstitial eosinophils, and exocytosis of lymphocytes. These findings suggest a pathophysiologic process that is immunologically based.
Morphologic and 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.
The presence of immunoglobulin and complement deposits in the skin of some patients with papular urticaria suggests that the lesions may be due to a cutaneous vasculitis. The deposits were most frequently seen in lesions within 24 hours of their development. The presence of granular deposits of Clq, C3, and immunoglobulin M (IgM) in superficial dermal blood vessel walls suggests that immune complexes (IgM aggregates) may be primarily involved in the pathogenesis, with complement activation initiated by Clq through the classic pathway. A T helper 2 (Th2) shift may be present, similar to what is observed in atopy.
In a study of the specific pattern of flea antigen recognition by IgG subclass and IgE during the progression of papular urticaria caused by flea bite, variations in the antibody responses of both subclasses to flea antigens were identified. Among these 25 patients, those with 2-5 years of papular urticaria had more IgE bands than patients with shorter or longer durations of symptoms. Thus, the predominant specific antibody isotypes appear to vary according to the time elapsed from the onset of fleabite-induced papular urticarial. The cellular immune response against whole-flea antigen in patients with papular urticaria by flea bites may be the result of an impaired dendritic cell population.
- The treatment of papular urticaria should be conservative and is symptomatic in most cases.
- Mild topical steroids and systemic antihistamines for relief of the itching that often accompanies this condition may be used.
- On occasion, papular urticaria may be severe enough to warrant the use of short-term systemic corticosteroids.
- If secondary impetigo occurs, topical or systemic antibiotics may be needed. Note that the use of insect repellents while the patient is outside and the use of flea and tick control on indoor pets are necessary when these individuals are being treated for papular urticarial.
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