You are in: eMedicine Specialties > Dermatology > ALLERGY AND IMMUNOLOGY Urticaria, PapularArticle Last Updated: Aug 11, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Robert A Schwartz, MD, MPH, Professor and Head of Dermatology, Professor of Medicine, Professor of Pediatrics, Professor of Pathology, Professor of Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School Robert A Schwartz is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and Sigma Xi Editors: Alexa F Boer Kimball, MD, MPH, Associate Professor of Dermatology, Harvard University School of Medicine; Vice Chair, Department of Dermatology, Massachusetts General Hospital; Director of Clinical Unit for Research Trials in Skin (CURTIS), Department of Dermatology, Massachusetts General Hospital and Brigham and Women's Hospital; David F Butler, MD, Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Scott and White Clinic; Director Dermatology Residency Training Program, Scott and White Clinic; Jeffrey J Miller, MD, Associate Professor, Department of Dermatology, Penn State University, Milton S Hershey Medical Center; Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University; Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center Author and Editor Disclosure Synonyms and related keywords: urticaria, papular urticaria, insect bites, type I hypersensitivity reaction, id reaction, bug bites INTRODUCTIONSection 2 of 12
  BackgroundPapular 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.1 Papular urticaria tends to be evident during spring and summer months. However, in some climates, such as in San Francisco, California, this condition may affect children throughout the year. PathophysiologyThe 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.1 Papular urticaria is generally regarded to be the result of a hypersensitivity or id reaction to bites from insects,2 such as mosquitoes, gnats, fleas, mites,3, 4 and bedbugs.5, 6 Varicella vaccines have also been implicated.7 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.8 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 classical pathway. FrequencyUnited StatesThe incidence is unknown. InternationalThe incidence is unknown. Mortality/MorbidityThe main morbidity is the discomfort due to localized pruritus. RaceNo racial predisposition is known, although certain ethnic groups, specifically Asians, may be more predisposed to more intense reactions. SexNo sexual predisposition is known. AgeThis eruption occurs primarily in children, but they eventually outgrow this disease, probably through desensitization after multiple arthropod exposures.9 This condition, however, can also occur in adults, albeit at a much lower rate. CLINICALSection 3 of 12
HistoryPatients report usually chronic or recurrent episodes of a papular eruption that tends to occur in groups or clusters associated with intense pruritus. Physical
CausesA hypersensitivity reaction to the bites of mosquitoes, fleas, bedbugs, and other insects causes papular urticaria. It is unusual to identify an actual culprit in any given patient.11, 12 DIFFERENTIALSSection 4 of 12
Dermatitis Herpetiformis Id Reaction (Autoeczematization) Impetigo Insect Bites Pityriasis Lichenoides
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| Drug Name | Triamcinolone 0.1% cream (Aristocort) |
|---|---|
| Description | Indicated for the treatment of dermatitis. Midpotency topical corticosteroid that inhibits cell proliferation. Has immunosuppressive and anti-inflammatory properties. |
| Adult Dose | Apply sparingly bid/qid as severity warrants |
| Pediatric Dose | Administer as in adults |
| Contraindications | Documented hypersensitivity; herpes simplex infection; fungal, viral, or tubercular skin lesions |
| Interactions | None reported |
| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus |
| Precautions | May cause adverse systemic effects if used over large areas, on denuded areas, on occlusive dressings, or during prolonged treatment periods |
| Drug Name | Prednisolone |
|---|---|
| Description | Decreases inflammatory reactions by suppressing migration of polymorphonuclear leukocytes and reducing capillary permeability. |
| Adult Dose | 40-60 mg/d PO divided 1-2 doses/d |
| Pediatric Dose | 0.5-2 mg/kg/d PO divided 2-4 doses/d |
| Contraindications | Documented hypersensitivity; viral, fungal, or tubercular skin lesions |
| Interactions | Decreases effects of salicylates and toxoids (for immunizations); phenytoin, carbamazepine, barbiturates, and rifampin decrease effects |
| Pregnancy | C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus |
| Precautions | Caution in hyperthyroidism, osteoporosis, cirrhosis, nonspecific ulcerative colitis, peptic ulcer, diabetes, and myasthenia gravis |
These agents are type 1 histamine receptor blockers that act to block the action of histamine after its release from mast cells and basophils. They are most effective when used prophylactically. Two classes of antihistamines exist: sedating and nonsedating. Typically, the sedating antihistamines are stronger and have more anticholinergic adverse effects.
| Drug Name | Cetirizine (Zyrtec) |
|---|---|
| Description | Indicated for the treatment of allergies. Forms a complex with histamine for H1-receptor sites in blood vessels, GI tract, and respiratory tract. |
| Adult Dose | 5-10 mg PO qd |
| Pediatric Dose | <2 years: Not established 2-5 years: 2.5 mg PO qd >5 years: Administer as in adults |
| Contraindications | Documented hypersensitivity |
| Interactions | Increases CNS toxicity of depressants |
| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals |
| Precautions | Caution in hepatic or renal dysfunction; doses >10 mg/d may cause drowsiness |
Therapy must cover all likely pathogens in the context of this clinical setting.
| Drug Name | Erythromycin (E-Mycin, E.E.S., Ery-Tab, Eryc, Erythrocin) |
|---|---|
| Description | Inhibits bacterial growth, possibly by blocking dissociation of peptidyl t-RNA from ribosomes causing RNA-dependent protein synthesis to arrest. In children, age, weight, and severity of infection determine proper dosage. When bid dosing is desired, half-total daily dose may be taken q12h. For more severe infections, double the dose. |
| Adult Dose | 250 mg erythromycin stearate/base (or 400 mg ethylsuccinate) PO q6h 1 h ac or 500 mg q12h Alternatively, 333 mg PO q8h; increase to 4 g/d depending on severity of infection |
| Pediatric Dose | 30-50 mg/kg/d (15-25 mg/lb/d) PO divided q6-8h; double dose for severe infection |
| Contraindications | Documented hypersensitivity; hepatic impairment |
| Interactions | Coadministration may increase toxicity of theophylline, digoxin, carbamazepine, and cyclosporine; may potentiate anticoagulant effects of warfarin; coadministration with lovastatin and simvastatin increases risk of rhabdomyolysis; decreases metabolism of repaglinide, thus increasing serum levels and effects |
| Pregnancy | B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals |
| Precautions | Caution in liver disease; estolate formulation may cause cholestatic jaundice; GI adverse effects are common (give doses pc); discontinue if nausea, vomiting, malaise, abdominal colic, or fever occur |
These agents have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body's immune response to diverse stimuli.
The authors and editors of eMedicine gratefully acknowledge the contributions of previous authors, Adam S. Stibich, MD, and Christy Shaffer, to the development and writing of this article.
| Media file 1: Papular urticaria. | |
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Article Last Updated: Aug 11, 2008
