WSAVA Nov 2021 Proceedings - Flipbook - Page 35
0013
DIAGNOSTIC APPROACH FOR THE ITCHY DOG AND
CAT
M. Tunhikorn
Bangkok/Thailand
Qualifications:
Maturawan Tunhikorn
DVM, DipACVD
maturawan.tun@mahidol.edu
Diagnostic approach for the itchy dog and cat
Itch or pruritus is one of the major problems that pet owners often bring
their animals to the veterinarian. Animals can exhibit pruritus in various
ways, such as licking, scratching, biting, scooting, or rubbing. Numerous
skin diseases can cause itch, both dermatologic and nondermatologic,
making the list of differential diagnoses very long. The most common
causes of itch are from ectoparasitic infestation, allergies, and infections.
There can also be a combination of more than one disease-causing pruritus in an individual animal. To identify the cause of the itch, the clinician
must obtain a thorough general and dermatological history and physical
examination to determine the list of differential diagnoses. Once the list
has been formed, the clinician can select the most appropriate tests and
follow them in proper order to rule in or rule out the suspected cause.
The diagnostic approach for pruritic animals should involve the following
1. Acquire a detailed history both general and dermatological
2. Perform a thorough physical and dermatological examination
3. List and prioritize the possible diagnoses
4. Perform the required tests/treatment trial, collect the information,
perform further investigation (if needed) and establish a diagnosis
History
Obtaining a detailed and accurate history is of great importance in the
diagnosis of pruritic skin diseases. Skipping this part could lead to misdiagnosis, waste of time and money, and cause frustration to the veterinarian and owners. The clinician should develop the skill of questioning the
owner. A questionnaire can be of great help, so the essential questions
are not missed. Examples of questions regarding pruritus are:
• Is the animal itchy? some owners are not aware that their pet is pruritic.
Since itch can manifest in different ways, asking specific questions (e.g.,
does your dog rub itself with furniture or does your cat lick itself) would
give you more information than asking whether the dog or cat is itchy.
Some cats are closet-licker, and the owner has no idea that the cat is
itchy.
• What is the age of onset? Pruritus starting at a younger age is more
likely from ectoparasitic infestation (scabies, fleas). Allergies can develop
in young to middle-aged animals with atopic dermatitis starting at around
6 months to 3 years old. Hormonal skin diseases, such as hyperadrenocorticism or hypothyroidism, most often develop in middle-aged to senior
dogs.
• Is it acute or chronic onset pruritus? Acute onset of pruritus is often
seen in ectoparasitic infestations such as scabies, fleas, or food allergy.
Allergies often are chronic; a dog with atopic dermatitis may lick its feet
constantly since a puppy.
• Where did the itch start, and how did it progress? Some diseases have
their characteristic pattern. A dog with scabies might start scratching its
ears, then the elbows, abdomen, and hock before becoming generalized.
Atopic dermatitis is often characterized by pruritus of the face, ears, anterior flexure fold, distal limbs. Flea allergy dermatitis usually involves the
dorsolumbar region, whereas flea infestation involves more of the ventral
aspect of the body.
• Is it itch before rash VS rash before itch? Non-lesional pruritus is most
likely due to allergies. Skin lesions (e.g., papules, pustules, crusts, excoriations) appear later due to self-trauma or secondary infections. Psychogenic pruritus can also start with no lesions. If the animal had lesions
before becoming itchy, it is more likely from ectoparasite infestation (e.g.,
scabies, cheyletiellosis) or infections.
• What is the itch level score (scale of 0-10)? Asking the owner about the
severity of the pruritus can give an idea of the disease-causing the problem. Canine scabies can be very pruritic, whereas demodicosis shows very
mild pruritus if no secondary infection is present. However, the severity of
the itch depends on the owner’s observations and is not always accurate. The itch level score is helpful to help determine whether the animal
response to the treatment when it is back for a recheck exam.
• Is the problem year-round? Seasonal pruritus is frequently associated
with atopic dermatitis, flea allergy dermatitis, and chigger mites, while
adverse food reactions cause non-seasonal pruritus.
• Any parasites observed on the animal and other household members?
Sometimes fleas, lice, or cheyletiella can be observed with naked eyes.
• Are other in-contact animals or humans have skin issues? If other in-contact animals also developed skin diseases, it is most likely from ectoparasitic infestation, for example, scabies or cheyletiella. Dermatophytosis can
likewise affect both animals and humans. Other zoonotic skin diseases
are scabies, cheyletiellosis, ear mites (rare).
• What are the current and previous diets, treats, and supplements?
Adverse food reactions can cause severe pruritus with acute onset. Based
on the diet information, the clinician can formulate a diet for a food trial.
• Are there any gastrointestinal problems (e.g., soft stool, vomiting)? Consider adverse food reactions in dogs or cats which have GI signs.
• What is the response to previous treatment? What was the current
medication? What is the patient’s response to glucocorticoid administration? The information helps the clinician to learn what medication worked
and not worked. Poor response to glucocorticoid raises the suspicion of
scabies.
Physical examination
Thorough physical examination is essential, both general and dermatological. The clinician should assess whether there is any lesion on the animal.
If so, were they primary lesions or secondary lesions? What are the distribution and pattern? Is it symmetrical or asymmetrical? Is it generalized or
localized? Lesion localization for canine scabies would be the ear margin,
elbows, ventral abdomen, and hock joints. Atopic dermatitis in dogs tends
to be localized at the face, ears, feet, flexure surface, and skin folds. Cats
are different than dogs in that they usually present with four reaction
patterns. The reaction patterns in cats include:
Miliary dermatitis.
Self-induced alopecia.
Head and neck pruritus.
Eosinophilic granuloma complex
List and prioritize the possible diagnoses
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