Urticaria

Urticaria

Urticaria is a transient eruption of erythematous (red) or edematous swelling of the dermis (Wheal) and usually associated with itching. 

Pathogenesis: How it occurs?
Allergens bind to IgE receptors on mast cells leading to their degranulation and release of histamine and other inflammatory mediators which result in capillary dilatation (causing redness seen at site of hives) and leaking of fluid into interstitial space (resulting in edema and swelling).

Mast cell degranulation in response to allergen
binding to their IgE receptos

Etiological factors: many factors may be associated with urticaria like :
-Drugs : penicillin, morphine & NSAIDs
-Foods: seafood, strawberries, nut, cheese & food additives.
-Insect bites and stinges.
-Inhalants : pollens &animal denders.
-Parasitic infestations: ankylostoma & ascaris.
-Infections.
-Emotional stress. 

Types of Urticaria:

-Papular urticaria : It's a form of urticaria that occurs in response to insect bites such as mosquitoes, flea and bedbugs. It's more common in children and young adults.  

papular urticaria in a child

Physical urticaria : It's caused by physical agents like cold, heat, sunlight, pressure and sweating. Dermographism "skin writing''  is a type of physical urticaria in which scratching or stroking the skin produces raised wheals along the scratch line.  

Dermographism note how skin lesions "wheals"
take the same pattern as the skin was stroked.

-Angioedema: It's an edema of the deep dermis and subcutaneous tissue it affects distensible tissues like eyelids,lips,lobes of ears and external genitalia. It may also affect mucous membranes like the larynx which is a life threatening condition.

Angioedema of eyelids

Treatment of Urticaria:
-Detection and avoidance of the triggering factor.
-Antihistamines.
-Corticosteroids. 
-adrenaline : in severe cases with angioedema.
Topical antipruritic e.g. calamine lotion.