Changes

==History and clinical signs==

==History and clinical signs==

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.

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. 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. 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 and treatment==

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.  

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.  

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 investigation of 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. 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 investigation of 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.