Allergic Dermatoses (I-III)

Most common lesion distribution of flea bite hypersensitivity

DORSAL

- dorsal lumbosacral area

- caudomedial thighs

- ventral abdomen

- flank

Lesion distribution of food/environmental allergies

VENTRAL

- head shaking

- face rubbing

- foot licking (top and bottom)

- belly scratching (ventrum, axilla)

- scooting

4 major feline inflammatory skin reaction patterns

Miliary dermatitis - papules, crusts

Self induced symmetrical alopecia

Head and neck pruritus/dermatitis

Eosinophilic granuloma complex

What are the 3 components of eosinophilic granuloma complex?

- eosinophilic plaques

- eosinophilic granulomas

- indolent ulcers

Common locations for indolent ulcers

- paw pads

- roof of mouth

- front limbs

- top of the tongue

- under the chin

- upper lip

Characteristics of eosinophilic plaques

- produce a moist, serous discharge

- common on the ventral abdomen

Primary feature of skin allergies is...

Pruritus

6 differential categories for pruritus

P-A-I-N

Parasitic

Allergic

Infectious/immune mediated

Neuropathic/neoplastic

Neoplasias that can cause pruritus

- mast cell

- histiocytic

- mammary

Manifestations of pruritus in dogs

- licking

- rubbing

- rolling

- biting/chewing

- scratching

Manifestations of pruritus in cats

- over grooming

- rubbing

- rolling

- biting/chewing

- scratching

3 most common causes of pruritus

- flea bite hypersensitivity

- food allergy

- atopic dermatoses

Characteristics of flea infestations

- minimal to no pruritus

- possible blood loss

Characteristics of flea bite hypersensitivity

- pruritus

- can be seasonal or non seasonal

- skin lesions present if infestation

- may or may not actually see fleas

Diagnosis of flea infestation

- history

- distribution of lesions

- finding fleas or flea dirt

- possible anemia

Primary lesions of flea bite hypersensitivity

- papules

- crusts

Secondary lesions of flea bite hypersensitivity

- alopecia

- scaling

- hyperpigmentation

- lichenification

Management of flea bite hypersensitivity

- eliminate fleas on the animal

- treat all in contact dog

- eliminate fleas in environment

- anti pruritic therapy

- assess and treat for secondary bacterial or Malassezia dermatitis

Anti pruritic therapy options for flea bite hypersensitivity

Glucocorticoids

Apoquel, zenrelia

Cytopoint

What are food intolerances?

- have no immunologic basis

- idiosyncratic reactions to certain foods or active substances

- do not cause pruritus or dermatologic disease

Pathogenesis of food allergies

- immunologically mediated

- loss of tolerance to food antigens

- altered GI permeability

- altered local immune surveillance

- dysbiosis of gut microbiome

True or false: food allergies have a genetic predisposition.

True

What type of hypersensitivity is food allergies?

Type IV - delayed type

Signalment of food allergy patients

Bimodal distribution

< 1 year old

OR

Somewhere in adulthood and have been eating the same ingredient for 2+ years

Food sensitivities are generally centered around what ingredient?

Proteins

Clinical signs of food allergies in dogs

- initially pruritus and/or diffuse erythema

- self trauma including alopecia, excoriations, crusts

- eventually chronic inflammation causing hyperpigmentation and lichenification

- recurrent pyoderma without pruritus

- uncommonly urticaria and angioedema

Environmentally induced and food induced atopic dermatitis can mimic...

Scabies

Potential sequelae of food allergies in dogs

Secondary superficial pyoderma - papules, pustules, crusts, moth eaten alopecia, epidermal collarettes

Secondary yeast dermatitis - erythema, waxy/oily debris, rusty discoloration

What concurrent GI signs may be present in food allergies?

- diarrhea

- soft stools

- frequent stools (3+ bowel movements per day)

True or false: clinical signs alone cannot differentiate food allergies from environmental allergies.

True

Distribution of feline food allergies

- face

- head and neck

- generalized

- pruritic otitis

- conjunctivitis

- hypersalivation

Diagnosis?

Food/environmental allergies

Diagnosis?

Flea bite hypersensitivity

Diagnosis of food allergies

- history (consistently non seasonal)

- clinical signs (big 5)

- dietary elimination and challenge trials

What common techniques are not helpful in diagnosing food allergies?

- intradermal testing

- prick and patch testing

- gastroscopy and colonoscopy

- hair testing

- saliva testing

- serologic testing (measure type I hypersensitivity, not type IV)

What is the most common food allergen category?

Proteins - usually a short run of amino acids

Common food allergens in dogs

- beef

- dairy

- chicken

- wheat

- corn

- soy

Common food allergens in cats

- beef

- fish

- chicken

Pathogenesis of food allergen cross-reactivity

Allergen amino acid sequences may be conserved in similar species or between species

Animals allergic to chicken may be cross reactive to..

- eggs, other poultry

- fish (white fish, salmon)

Animals allergic to beef may be cross reactive to...

- lamb, venison, bison

- dairy

Animals allergic to yellow mealworm may be cross reactive to...

- house dust mites

- storage mites

Problem with home cooked limited ingredient diets in food trials

- owner intensive so unlikely to be consistent

- unlikely to be balanced

Problem with commercial limited ingredient diets in food trials

Tend to be contaminated

Problem with novel protein prescription diets in food trials

- difficult to find "novel" ingredients, especially with unknown dietary history

- concerns regarding cross reactivity among sources

What diets should we choose for diet trials?

Hydrolyzed protein diets

Use the lowest MW available

How long should a food trial be?

8 weeks minimum

Duration may be shortened by using anti-inflammatories for the initial 2-4 weeks (apoquel, pred)

Important considerations for food trials

- gradual transition

- no other foods, treats, supplements, flavored pills, chew toys

- must resolve secondary skin and ear infections before the end of the trial

What is a food challenge?

If improvement is noted, the patient is placed on their previous diet to see if clinical signs recur

Can also do this if we don't think the food trials worked

True or false: environmental and food allergens can occur concurrently.

True

What is canine atopic dermatitis?

A hereditary, typically pruritic and predominantly T cell driven inflammatory skin disease involving the interplay between...

- skin barrier abnormalities

- allergen sensitization

- microbial dysbiosis (smaller populations of bacteria on the skin)

Pathogenesis of CAD

Abnormal skin barrier - disrupted epidermal lipid barrier facilitates allergen uptake

Langerhans cells and TH2 cells trigger production of allergen specific IgE and sensitization

Allergen exposure -> mast cell degranulation -> release of mediators of pruritis and inflammation (IL-31)

True or false: there is a genetic component to CAD.

True

Breed disposition to CAD

- WHWT

- labs

- goldens

- boxers

- GSD

- frenchies

What is feline atopic syndrome? (FAS)

Allergic diseases of the skin, GI tract and respiratory tract

What is feline atopic skin syndrome? (FASS)

Allergic skin disease caused by environmental allergens

Pathogenesis of FASS

T cell involvement

IgE involvement but unsure of extent

Exposure to environmental allergens appears to exacerbate

Common allergens/triggers for atopic dermatitis

- pollens (grass, tree, weed)

- house dust mites

- molds

- foods

History of patients with canine atopic dermatitis

Pruritus beginning early in life - 6 months to 6 years old, peak age of onset 1-3 years (or, 1-3 years of exposure to their environment)

May begin as seasonal or non seasonal pruritus, but most become non seasonal by middle age

Clinical signs increase in duration and severity

Lesion distribution of canine atopic dermatitis

BIG 5 - in general, ventral distribution

- ears

- periocular, muzzle

- feet

- axillae, inguinal

- perivulvar, perianal

What secondary dermatoses may result from atopic dermatitis?

- superficial pyoderma

- Malassezia dermatitis

- seborrhea

- unilateral or bilateral otitis externa (bacteria, Malassezia, or both)

Feline reaction patterns to feline atopic skin syndrome (FASS)

- miliary dermatitis

- self induced alopecia

- head and neck ulcerative dermatitis

- eosinophilic dermatitis (plaques, granulomas, indolent ulcers)

What history rules out food allergies?

Seasonality

Which diagnostic tests should NOT be used for atopic dermatitis?

Intradermal and serologic tests

What are the 5 components of canine atopic dermatitis?

- genetics

- immunologic abnormalities

- skin barrier abnormalities

- allergen sensitization

- microbial dysbiosis

Which type of therapy is most successful at managing CAD?

Multimodal therapy

What are the 5 broad ways we can go about treating CAD?

- spay and neuter

- identify and limit exposure to environmental and food allergens

- control and prevent hypersensitivity reactions and flares

- manage and prevent dysbiosis/overgrowth/infection

- reduce and prevent transepidermal water loss/absorption of allergens

Drug options for acute flares of CAD

- corticosteroids

- janus kinase inhibitors

- monoclonal Ab injections

Drug options for chronic management of CAD

- janus kinase inhibitors

- monoclonal Ab injections

- calcineurin inhibitors (tacrolimus, cyclosporine)

- immunotherapy

- corticosteroids

When is it ideal to use corticosteroids?

We need a fast and potent response

Ideal for short seasonal signs, acute flares (days/weeks)

What corticosteroids should ideally be used for CAD?

Oral, short acting (pred)

Avoid injectables

What are examples of janus kinase inhibitors?

Oclacitinib (Apoquel)

Ilunocitinib (Zenrelia)

Atinvicitinib (Numelvi)

MOA of janus kinase inhibitors

Inhibit JAK pathways, blocking cytokines involved in pruritus and inflammation such as...

IL-2, 4, 6, 13, 31

Efficacy of janus kinase inhibitors

May work as fast as corticosteroids in reducing pruritus

Benefit in 80-85% of patients

What are examples of monoclonal antibody therapies?

Lokivetmab (Cytopoint)

Tirnovetmab (Befrena)

MOA of monoclonal antibody therapies

Caninized monoclonal antibody against circulating IL-31 (which is a pruritogenic cytokine)

Efficacy of monoclonal antibody therapies

Benefits 85-90% of dogs

Rapid acting

Benefits of monoclonal antibody therapies

- rapid acting

- safe to be used in dogs with concurrent disease

- no minimum age for dogs

Examples of calcineurin inhibitors

Cyclosporine - Atopica, Cyclavance, Sporimmune

Tacrolimus (topically)

MOA of calcineurin inhibitors

Blocks activation of IL-2, inhibits T cell proliferation

Downsides of calcineurin inhibitors

May take up to 4 weeks to see effect, up to 8 weeks for max benefits

Cost can be limiting factor in dogs

Benefits of calcineurin inhibitors

Good maintenance therapy for cats

MOA of allergen-specific immunotherapy

Modifies the immune response to specific allergens

Allergen selection based on intradermal test, serology, and patient history

Allergen-specific immunotherapy is especially indicated for...

Younger adult animals

Administration of immunotherapy

Subcutaneous or sublingual

Efficacy of allergen-specific immunotherapy

50-60% success (esp bc compliance issues)

Benefits of allergen-specific immunotherapy

- spare other medications

- improve quality of disease management

- only treatment to prevent development of new hypersensitivities

Downsides of allergen-specific immunotherapy

- 3 to 12 month onset of benefits

- most patients require additional support

How can we prevent reduction in diversity of the microbiome?

- increased use/reliance on topicals

- minimize use of abx

- control inflammation

Skin barrier function depends primarily on what structure?

The stratum corneum

Skin barrier dysfunction is largely attributed to what anatomical abnormality?

Altered ceramides (in the lipid layer of the stratum corneum)

Abnormal epidermal barriers can result in...

- increased transepidermal water loss

- increased penetration of allergens

Treatment options for the skin barrier

- topical and oral essential fatty acids

- topical sphingolipids/ceramides

- nutritional support

- botanicals

- hydrotherapy

How can we reduce allergen exposure?

Minimize environmentally-induced triggers

- frequent wiping, bathing, rinsing

- avoid outdoor activities on mowing or windy days

- HEPA filters

- frequent laundry washing

- vacuum often

What is acral lick dermatitis in dogs?

Urge to lick the distal cranial portion of the limb

Clinical presentation of acral lick dermatitis

- thickened plaques

- erythema

- erosions/ulcers

- draining tracts

Complication associated with acral lick dermatitis

Licking/self trauma predisposes to secondary bacterial infection - deep pyoderma almost always results

Causes of acral lick dermatitis

- allergies

- joint pain

- foreign body

- neuropathy

- psychogenic (bored, anxiety)

Treatment for acral lick dermatitis

- treat the secondary bacterial infection

- allergy work up

- lesion treatment (oral/topical steroids, oclacitinib, laser, neuropathic pain meds)

- physical restraint