here - Australian College of Veterinary Scientists

years, median age 6.5 years, with age of onset of disease 1-27 years (median 5.5 years)
and duration of clinical signs at time of referral ranging from 2 months to >5years.
Fourteen of the horses presented with pruritus and six with pruritus and urticaria.
Four horses had recurrent or chronic urticaria without obvious pruritus, including
one with angio-oedema. The degree of pruritus was considered to be severe in six
animals, and was particularly severe in case 3 (see figure 1) resulting in self inflicted
damage and requiring the use of a nosebag to prevent biting. In most cases the
clinical signs were restricted to the trunk, with tail rubbing also present in seven,
mane involvement in two and facial irritation noted occasionally. Papules or
“bumps” were reported or found on dermatological examination in six cases. Two
horses had histories of intercurrent respiratory problems thought to be of allergic
aetiology on the basis of previous investigations (endoscopy and cytological
examination of tracheo-bronchial washes). In 12 horses the clinical signs were
perennial, with exacerbation in the summer noted in two and winter exacerbation in
two others. Four animals showed a seasonal pattern to their skin problem, one of
which was restricted to spring, two to the winter and the fourth to the summer. This
latter horse was only stabled in the summer and turned out all winter. In eight
animals the duration of clinical signs was not long enough to determine if the
problem was going to be perennial, but in six the signs began in autumn or winter
and two started with symptoms in late summer or autumn. All animals were stabled
for at least 50% of the day, with 15 horses being stabled full time at the time of
maximal clinical signs.
Diagnosis:
A large number of differential diagnoses may need to be considered, depending on
the history and distribution of clinical signs, but would include:
insect hypersensitivity
ectoparasites (lice, chorioptic mange, psoroptic mange, trombiculidiasis,
poultry mites)
oxyuriasis
forage/storage mites
helminth infestations (oxyuriasis, strongyloidosis, Pelodera cutaneous larval
migrans)
contact dermatitis
adverse cutaneous food reaction
drug reactions
systemic diseases causing pruritus (rare cases of lymphoma, hepatic and renal
neoplasia)
As in the dog and cat, the diagnosis of atopic dermatitis is reached after ruling out all
other possible differentials and the diagnosis is essentially a clinical diagnosis.
Laboratory investigations such as routine haematological and biochemical profiles
are rarely contributory to reaching a diagnosis in atopic horses, but may be indicated
to investigate possible systemic disease in cases with suggestive clinical signs. Skin
ACVSC Proceedings Dermatology Chapter Science Week 2005 13