Allergic Skin Disease

Question 1

How is atopy properly diagnosed? What is not used for a definitive diagnosis?

Answer 1

ruling out other diseases

intradermal serum allergy testing

Question 2

What signalments are associated with flea allergy dermatitis, atopy, food allergy, and contact dermatitis?

Answer 2

FAD - no age predilection, tends to be over 6 m/o

ATOPY - 1-3 y/o, WHWT and English Bulldog predisposed

FOOD - any age, often <1 y/o and older patients

CONTACT - no age predilection

Question 3

What is onset of flea allergy dermatitis like?

Answer 3

rapid, especially in warmer weather

Question 4

What is onset of atopy like?

Answer 4

gradual onset, depends on what patient is allergic to

• house dust mite = non-seasonal
• grass pollen = summer
• year-round signs possible with worsening during particular months

Question 5

What is onset of food allergy like?

Answer 5

non-seasonal, usually gradual onset

Question 6

What is onset of contact dermatitis like?

Answer 6

rapid onset, depends on what patient is allergic to

• carpet = non-seasonal
• plant = seasonal

Question 7

What are the classical lesions of allergic diseases?

Answer 7

• excoriations
• alopecia
• erythema
• hyperpigmentation
• lichenification

Question 8

What is the classical distribution of lesions associated with flea allergy dermatitis? What is commonly not associated?

Answer 8

caudal half of the body around the dorsal lumbosacral region, tailbase, perineum, thighs, and umbilicus (++++ pruritic)

lesions on ears

Question 9

What is the classical distribution of lesions associated with atopy?

Answer 9

face, paws, distal extremities, ears, ventrum

(++++ pruritic)

Question 10

What is the classical distribution of lesions associated with food allergy?

Answer 10

face, paws, distal extremities, ears, ventrum

(+/- pruritic)

Question 11

What lesions are characteristic of contact allergy? What is the classical distribution? What is not associated?

Answer 11

vesicles and erythematous papules (+++ pruritis)

hairless areas readily in contact with environment - abdomen, muzzle, ventral of paws

lesions on ears, unless associated with ear medication

Question 12

What is a unique lesion seen in cats with allergic skin disease? What are 2 examples?

Answer 12

reaction patterns

1. miliary dermatitis - diffuse crusted papules
2. eosinophilic granuloma complex

Question 13

Other than reaction patterns, what are 4 unique presentations of allergic dermatitis in cats?

Answer 13

1. indolent ulcer - symmetrical lesion of the upper lip
2. eosinophilic granuloma - mouth or body
3. eosinophilic plaque - linear papules on caudal thighs
4. flea allergy dermatitis - caudal dorsal, symmetrical alopecia, face/neck

Question 14

What are the preferred diagnostics for flea allergy dermatitis, atopy, food allergy, and contact allergy?

Answer 14

FAD - distribution of lesions, flea or flea dirt, 2-3 month treatment trial

ATOPY - r/o other differentials, environmental allergy testing is best used to make a vaccine, not a dx

FOOD - diet trial with hydrolyzed protein or novel protein diets (serum tests are NOT accurate)

CONTACT - patch test (type 4 sensitivity = serum and intradermal testing is inaccurate)

Question 15

What are 5 steps to the rule-out process when diagnosing allergic skin disease?

Answer 15

1. r/o infectious disease, like Sarcoptes, Dermatophytosis, and Demodex
2. r/o FAD with an 8 week trial with strict flea control for all animals in the household
3. r/o food allergy with an 8-12 week elimination diet
4. perform a patch test if distribution and history matches contact allery
5. if all have been ruled out, consider atopy and proceed to intradermal testing (gold standard) or serum allergy testing to develop allergy-specific immunotherapy