Changes

==Pathogenesis==

==Pathogenesis==

The aetiopathogenesis of urticaria is complex and many causes have been suggested. The basic pathogenesis is thought to be due to degranulation of mast cells and basophils leading to the release of inflammatory mediators and an increase in vascular permeability. The condition may occur due to exogenous or endogenous hypersensitivity reactions. Exogenous urticaria may occur as a result of exposure to chemicals, medication and insect bites or stings. Endogenous urticaria occurs following inhalation of allergens such as pollens.  

The aetiopathogenesis of urticaria is complex and many causes have been suggested. The basic pathogenesis is thought to be due to degranulation of mast cells and basophils leading to the release of inflammatory mediators and an increase in vascular permeability. The condition may occur due to exogenous or endogenous hypersensitivity reactions. Exogenous urticaria may occur as a result of exposure to chemicals, medication and insect bites or stings, shampoos or insecticides. Endogenous urticaria occurs following inhalation of allergens such as pollens.  

==Signalment==

==Signalment==

Because of the numerous underlying causes of urticaria, definitive diagnosis may be difficult. Historical and clinical findings may lead to suspicion of the condition. The localisation of lesions (e.g. site of contact with saddle or insect repellent) or history of medication or exposure to chemicals may help to determine an underlying cause.  

Because of the numerous underlying causes of urticaria, definitive diagnosis may be difficult. Historical and clinical findings may lead to suspicion of the condition. The localisation of lesions (e.g. site of contact with saddle or insect repellent) or history of medication or exposure to chemicals may help to determine an underlying cause.  

Acute urticaria often resolves spontaneouly without requiring treatment. Dexamethasone given once at a dose of 0.1 mg/kg IM usually results in resolution of clinical signs within 24 hours.  Recurrent cases may require further investigation in order to determine the underlying cause. This may include further questioning about the animal's history and response to withdrawal of drugs or topical products. If no underlying cause is found, an investigation for allergies is indicated and may include intradermal allergy testing, insect control trials and an elimination (novel protein) diet. Biopsy of lesions is generally unrewarding but may reveal a mild to moderate perivascular to interstitial dermatitis. Antihistamines such as Hydroxyzine may be useful in the management of chronic urticaria but are ineffective in treating acute urticaria. Acupuncture has been reported to be effective in one horse.

Acute urticaria often resolves spontaneouly without requiring treatment. If urticaria is susupected all current medications should be stopped. Dexamethasone given once at a dose of 0.1 mg/kg IM usually results in resolution of clinical signs within 24 hours.  Recurrent cases may require further investigation in order to determine the underlying cause. This may include further questioning about the animal's history and response to withdrawal of drugs or topical products. If no underlying cause is found, an investigation for allergies is indicated and may include intradermal allergy testing, insect control trials and an elimination (novel protein) diet. Biopsy of lesions is generally unrewarding but may reveal a mild to moderate perivascular to interstitial dermatitis. Antihistamines such as Hydroxyzine may be useful in the management of chronic urticaria but are ineffective in treating acute urticaria. Acupuncture has been reported to be effective in one horse.

==Prognosis==

==Prognosis==