Urticaria

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.

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

Signalment

Horses between 1 and 10 years of age are most prone to developing the condition. There is no sex predilection but Thoroughbreds and Arabs are thought to be more affected than other breeds.

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. Pruritus may or may not be present.

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) may help to determine an underlying cause or alternatively a history of medication or exposure to chemicals.

References==

• Pascoe, R. R., Knottenbelt, D. C. (1999) Manual of Equine Dermatology Elsevier Health Sciences
• Scott, D. W., Miller, W. H. (2003) Equine Dermatology Elsevier Health Sciences