Urticaria
causes: viral infections (respiratory -80% in children), drugs: beta-lactams, NSAIDs/aspirin, opiates, contrast media; foods- adults (shellfish berries nuts pork, chocolate, tomatoes, food additives, children: dairy wheat, eggs , citrus; inhalants - pollen, dust, mold, animal dander; emotional stress
acute: lasts for less than 6 weeks. - 95% of cases. does not require any lab workup.
chronic: lasts more than 6 weeks - consider workup.;usually caused by autoimmune urticaria, chronic infections (h pylori), physical urticaria, or idiopathic
physical urticarias: dermatographism is the most common physical urticaria and is present in up to 5% of the population. presents with wheals that occur within minutes of the skin being scratched.
urticaria DDX: urticarial like drug or viral exanthems: drug or viral induced urticaria type 1 hypersensitivity reaction. drug or viral induced urticaria like exanthema= type 4 hypersensitivity reaction. apaular urticaria and reactive erythemas (serum sickness, erythema multiform, erythema marginatum, and erythema chronic migrans)
serum sickness: type 3 hypersensitivity reaction to medications or infections. symptoms : fever, urticaria like lesions [look histologically and clinically like urticaria but can last greater than 24 hours], arthritis, low complement.
erythema multiform: acute self limited disease usally associated with herpes simplex virus infections. classes target papule and plaques. lesions may occur at any site, but palm and sole are most commonly involved. oral mucosal involvement is common but limited
erythema marginatum: this is an autoimmune reaction to specific strains of group A streptococcal pharyngitis. it is poorly understood but though tot be an antibody-mediated type 1 +/- delayed type hypersensitivity reaction (type 4). occurs 1-5 weeks after sore throat with : migratory poly arthritis of large joints, caritas, subcutaneous nodules on extensor forearms and Sydenham chorea) cutaneous manifestation of acute rheumatic fever. urticaria-like, migratory, annular, polycyclic, light pink, smooth edematous plaques that spread centigully. differfentiated from urticaria by lesions lasting hours to days nd neutrophilic inflammation on histology.
Erythema chronic migrans (ECM): pink to red examining annular patch +/- central clearing. 7-15 days after deer tick detachment. feature type disease. maybe associated with flu like illness. initially a single patch--> disseminated lesions can occur days to weeks after initial lesion.