Dog and Cat Allergic Skin Disease

The four major skin conditions affecting dogs and cats

flea allergy dermatitis, atopic dermatitis, food allergies, contact allergies

Age most common for food allergies in dogs

Younger ( < 1 year) and older dogs

Age of onset most commonly for clinical signs of atopy

1-3 years of age (6 mo - 6 yrs)

How to diagnose atopy

Diagnosis of exclusion, can’t be diagnosed with intradermal or serum allergy testing

Age of onset for flea allergy dermatitis

No age predilection; typically > 6 mo of age

Common allergy lesions in dogs (5)

erythema, excoriations, alopecia, hyperpigmentation, lichenification

Distribution of flea allergy dermatitis lesions

Caudal half of the body: dorsal lumbosacral, tailbase, perineum, thighs, umbilicus

-NOT EARS USUALLY

-pruritic

Distribution of atopy lesions

face, paws, distal extremities, ears, ventrum

-pruritic

Distribution of food allergy dermatitis lesions

same as atopy: face, paws, ears, distal extremities, ventrum

-may or MAY NOT be pruritic

Distribution of contact allergy lesions

hairless areas coming into contact with environment: abdomen, muzzle, ventrum of paws

-contact allergy to ear meds: ears

-primary lesions: vesicles, erythematous papules

-pruritic

Two reaction patters in cats

miliary dermatitis: diffuse crusted papules

eosinophilic granuloma complex

Four types of allergic skin disease in cats

indolent ulcer: ulcerative symmetrical lesion on the upper lip

eosinophilic granuloma: mouth or body

eosinophilic plaque: linear plaques on caudal thigh

flea allergy dermatitis: caudal dorsal, symmetrical alopecia, face, neck

Rule out process for pruritus

1. Rule out infectious disease: demodex, scabies, dermatophytosis

2. Rule out fleas; at leas 8 weeks of flea treatment and treat environment

3. Rule out food allergies with a 8-12 week strict diet

4. Patch test if considering contact allergies, or consider atopic dermatitis

5. If all are negative, consider atopy and perform intradermal test or serum allergy testing for allergy specific immunotherapy (vaccine)

4 main anti pruritic drugs

Apoquel (oclacitinib), Cytopoint (lokivetmab), Cyclosporin (Atopica), steroids (prednisone)

Key mediator of pruritis (cytokine) and what it activates

IL-31 activates the JAK/STAT pathway to cause pruritus and release pro-inflammatory cytokines

MOA janus kinase pathway

IL-31 activates JAK receptor→ JAK forms a dimer (two JAKS)→ activation of STAT→ STAT travels to the nucleus and causes transcription of proinflammatory cytokines and itch

MOA of apoquel

JAK inhibitor; targets JAK 1

-competitive inhibitor to the receptor for IL-31 which prevents JAK1 and STAT to be activated; blocks itch

MOA of cytopoint

monoclonal antibody that binds to IL-31 which prevents it from binding and activating the JAK/STAT pathway

MOA of prednisone

Inhibit pro inflammatory molecules and up regulate anti inflammatory mediators like lipocortin 1 (annexin 1)

MOA for cyclosporin

Calcineurin inhibitor; suppress cytokine IL-2 which blocks proliferation of T cells; reduces inflammation and the allergic response

Apoquel side effects

Increases susceptibility to Demodex, other infections

-exacerbate neoplasia

-GI : vomiting, diarrhea

-not for patients 1 yr of age (demodex) and severe infections (pneumonia)

Cytopoint side effects

-well tolerated

-no hypersensitivities shown

Cyclosporin side effects

GI upset is main

-increased hair growth ( hirsutism), papillomas, gingival hyperplasia → resolves after cessation of use

-decrease function of pancreatic B cells and influences dosing of insulin

-ihibits p-glycoprotein coded by ABCB1 (MDR1 gene)→ don’t give ivermectin

-substrate of cytochrome p450→ inhibition of p450 with ketoconazole can lower dose of cyclosporin needed

Prednisone side effects

PU/PD, polyphagia, behavioral changes, GI ulcers, hepatopathy, diabetes, hyperlipidemia, decreased thyroid hormone

-delayed wound healing, calcinosis cutis, cutaneous atrophy, comedones

-secondary infections: demodex, toxoplasmosis, UTI

DO NOT USE WITH NSAIDS → gi ulcers and renal failure

Pruritic medications for cats

Apoquel: not labeled

cytopoint: modified to only work in dogs

cyclosporin: used routinely

steroids: prednisolone