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==Description==

==Description==

Urticaria is a condition of the skin characterised by multiple oedematous swellings (wheals) that dent or 'pit' with digital pressure. It occurs in all domestic animals but most commonly in the horse.

Urticaria is a condition of the skin characterised by the development of multiple flat-topped, oedematous swellings (wheals) that dent or 'pit' with digital pressure. Episodes may be acute, chronic or recurrent. The condition occurs in all domestic animals but most commonly in the horse.

==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. Other hypotheses include exogenous or endogenous hypersensitivity reactions. Exogenous urticaria may occur due to chemicals, medication and insect bites or stings. Endogenous urticaria occurs due to inhalation of allergens.

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 due to inhalation of allergens.

==Signalment==

==Signalment==

==History and clinical signs==

==History and clinical signs==

Multiple wheals are often observed with urticaria and occur within a few minutes or hours of exposure to the causative agent. A history of recurrence or repeated episodes is often reported. Affected areas can vary from small, localised lesions up to 3cm in diameter, to extensive generalised areas involving large areas of skin. Lesions can occur on any part of the body but usually develop on the back, legs, flanks, neck and eyelids. In severe cases the mucous membranes of the nose, mouth, anus and vulva may be involved. . Pruritus may or may not be present and the lesions usually disappear rapidly.

Multiple wheals are often observed and occur within a few minutes or hours of exposure to the causative agent. A history of recurrence or repeated episodes is often reported. Affected areas can vary from small, localised lesions up to 3cm in diameter, to extensive generalised areas involving large areas of skin. Lesions can occur on any part of the body but usually develop on the back, legs, flanks, neck and eyelids. In severe cases the mucous membranes of the nose, mouth, anus and vulva may be involved. Pruritus may or may not be present and the lesions usually disappear rapidly.

==Diagnosis==

==Diagnosis==

Because of the numerous underlying causes of urticaria, definitive diagnosis may be difficult. Historical and clinical findings may lead to the suspicion of urticaria. The localisation of lesions (e.g. site of contact with saddle or insect repellent) or history of medication of exposure to chemicals may help to determine an underlying cause. Dermatographism is a specific pressure-induced type of urticaria in which wheals form in reponse to exogenous pressure. Commonly these are observed in the saddle area of the horse.  

Because of the numerous underlying causes of urticaria, definitive diagnosis may be difficult. Historical and clinical findings may lead to the suspicion of the condition. The localisation of lesions (e.g. site of contact with saddle or insect repellent) or history of medication of exposure to chemicals may help to determine an underlying cause. Dermatographism is a specific pressure-induced type of urticaria in which wheals form in reponse to exogenous pressure. Commonly these are observed in the saddle area of the horse.  

==Treatment==

==Treatment==