here - Australian College of Veterinary Scientists

Wheals vary in size and shape and quite arbitrarily may be divided into:
1. Conventional: 2-3mm up to 3-5mm.
2. Papular: multiple small uniform 3-6mm diameter wheals i.e. insect bites.
3. Giant: either single or coalesced multiple wheals up to 20-30cm diameter.
4. Annular: donut like lesions.
The lesion may present differently depending on the location of the oedema i.e.
whether it is in the upper layers of the dermis or subcutaneous and may be pruritic or
non pruritic.
1. "Oozing urticaria" - where dermal oedema is severe, oozing of serum from
the skin surface may occur. Care should be taken to distinguish this from an
erosive/ulcerative process or a pyoderma. NB lesion must still pit on pressure.
2. Gyrate urticaria - has been referred to as the dermal form of erythema
multiforme but it should be stressed that this syndrome is not related to 'true'
erythema multiforme which is primarily an epidermal disease (lesions DO NOT
pit on pressure). Drug reactions appear to be the most common cause of this
form of urticaria.
3. Angiooedema (Angioneurotic oedema) - a subcutaneous form of urticaria
which tends to be more diffuse due to lack of restraint to spread in the sub
cutis. Usually involves the head and extremities and is more indicative of a
systemic and serious disease than urticaria.
Diagnosis
Because of the numerous potential causes of urticaria a definitive diagnosis may only be
reached after extensive clinical and diagnostic investigation which can be time
consuming, expensive and often unrewarding. Horse owners usually are reluctant to
undertake the costly task of endeavouring to obtain an accurate diagnosis.
Initially, diagnosis is mostly based on clinical signs (mostly cutaneous reaction patterns)
and a careful history of the case. (Scott & Miller 2003)
History is important:
- Is it the first attack?
- If not, how many and are they seasonal?
- Site of lesions- is it a point of contact with gear?
- Use of any drugs, frequency and reaction at time of use, drenches,
medicated sprays, ointments, shampoos, ultrasound gel. Etc
- Pasture plants
Specific activities-exercise only induced
Being worked, (confirm by 30 min exercise producing urticaria) out
in paddock for pick of grass
- Food allergy can only be traced by elimination diets and then
challenge with suspected feed ( very time consuming with NO short
ACVSC Proceedings Dermatology Chapter Science Week 2005 43