View source for Wheal

==Background==
*In [[urticaria]] (hives), both wheals and [[angioedema]] are present. Wheals result from localized edema of upper dermis, while angioedema results from edema of lower dermal and subcutaneous tissues<ref>Bernstein JA, Moellman J. Emerging concepts in the diagnosis and treatment of patients with undifferentiated angioedema. Int J Emerg Med. 2012 Nov 6;5(1):39. doi: 10.1186/1865-1380-5-39. PMID: 23131076; PMCID: PMC3518251. </ref>
*Mast cell and basophil activation involving the release of vasoactive substances
*Broad differential diagnosis of etiologies
**Sometimes iatrogenic; for example, skin wheals from intradermal lidocaine infiltration, allergy skin prick test, tuberculin skin test

==Clinical Features==
* Papules that are well-circumscribed but irregular, pruritic, and often with a pale center and red flare on the borders
* Transient duration, usually hours, with spontaneous self-resolution
* If related to anaphylaxis or allergy, may also involve other systems such as respiratory, circulatory, GI 

[[File:Urticarial wheal.jpg|thumb|Urticarial wheal]]

==Differential Diagnosis==
*[[Anaphylaxis]]
*[[Acute allergic reaction]]
*[[Contrast induced allergic reaction]]
*[[Acute transfusion reaction]]
*[[Chronic urticaria]]
*[[Dermatographism]]
*[[Cold urticaria]]

==Evaluation==
*Clinical diagnosis
**Take a thorough history to assess for precipitating factors, including recent foods, travel, medications/treatments, insect bites/stings, autoimmune disease, viral infections, anaphylaxis history, etc
**Check for association with overlying objects such as watches, jewelry clothing, bands, etc

==Management==
* If any suspicion of anaphylaxis, treat with IM [[epinephrine]]
* 2nd gen H1 [[antihistamines]] are effective; if ineffective, consider  [[corticosteroids]] and H2 antihistamines<ref>Schaefer P. Acute and Chronic Urticaria: Evaluation and Treatment. Am Fam Physician. 2017 Jun 1;95(11):717-724. PMID: 28671445.</ref>
* Avoid any causative agent or medications if identified, and treat the underlying illness

==Disposition==
*Observe in ED for 4-6 hours until symptoms improve; utilize clinical gestalt
*If anaphylactic picture, after observation discharge with anaphylaxis emergency plan and epipen

==See Also==
*[[Angioedema]]
*[[Anaphylaxis]]
*[[Acute allergic reaction]]

==References==
<references/>

[[Category:Dermatology]]
[[Category:Symptoms]]