A patient with the primary client complaint of itch represents a common dilemma in skin disease.
In each canine or feline patient, several causes can contribute to overall pruritus. To identify specific causes and treat each patient accordingly, practitioners need a general understanding of the multiple causes of pruritus: yeast and bacterial infections, ectoparasites, atopic dermatitis complex (including environmental or food allergy), or atopic-like dermatitis.
Clinical Signs & Diagnosis
Historical and physical clues identified during client discussion can narrow the diagnosis (see Clinical Features of Pruritus: A Mental Chalkboard). Age and nature of onset can be helpful; although parasites or food allergy can occur at any age, environmental allergy often presents in young dogs and does not commonly begin in dogs older than 3 to 4 years of age. Evidence of contagion suggests parasite infestation or dermatophytosis (especially in cats). Concomitant GI signs may indicate food allergy.
Distribution is often (although not always) characteristic. Dorsal lumbosacral distribution suggests flea allergy dermatitis until proven otherwise. If distribution includes feet, face, ventrum, and/or pinnae (in any combination), environmental or food allergy should be considered. If ear margins, elbows, or ventrum are affected, scabies should be considered.
Basic in-house diagnostic procedures (eg, skin scrapings, skin cytology) can help rule out common and obvious causes. Fleas and Cheyletiella spp mites can be identified by brushing or combing the hair coat. Superficial and deep scrapings and hair pluckings are all required when looking for mites. Samples from lesions should be obtained by impression smear, scotch tape, or other collection methods to confirm staphylococcal or yeast infection on cytology.
|Diagnostic Criteria for Canine Atopic Dermatitis|
If 5 or more of these 8 criteria are confirmed and other differentials have been ruled out, atopic dermatitis is highly likely1:
How I Treat Pruritus
Provide cause-specific treatment when possible.
- If bacterial or yeast infection is identified, treat appropriately and without steroids.
- If moist, greasy, odiferous dermatitis with pronounced pruritus is present, treat for yeast, even if none is found on cytology.
- If parasites are identified, treat accordingly.
- Scabies mites can be difficult to find; treat empirically when scabies is suspected.
Consider short-term antipruritic treatment if no cause or infection is determined.
- Glucocorticoids (systemic or topical) and oclacitinib (Apoquel, apoquel.com; dogs only) are the most rapid-acting and effective for immediate use.1
- Cyclosporine A may take several weeks to work, making it less desirable for quick, short-term relief.
- Antihistamines are not typically effective.
Consider appropriate medicated shampoo.
- Before prescribing shampoo, confirm the client can bathe the patient.
Follow up by phone at 5–7 days to assess response, make a plan, and establish owner expectations.
- Ask the owner to call with a progress report.
- This reinforces clinician’s commitment and enables prompt recognition of client frustration.
- Follow up via phone if client does not call.
- Uncomplicated parasitic and infectious causes should respond to treatment, and further action may not be necessary.
- If response is minimal or incomplete or relapse occurs, schedule recheck at 2 weeks.
- Plan for additional patient time, and inform the client that additional diagnostics may be indicated.
Recheck in 2 weeks, if necessary.
- Determine what has and has not improved.
- Treatment of secondary infection will often provide a clearer picture of underlying disease.
- Consider starting hypoallergenic diet trial, if indicated.
- If a canine patient fulfills clinical diagnostic criteria for atopic dermatitis (see Diagnostic Criteria for Canine Atopic Dermatitis), consider testing for environmental allergy.
- If patient still has substantial lesions, consider skin biopsy or culture and susceptibility testing.
For chronic conditions, formulate a long-term management plan that is effective and acceptable to the client.
- Combine multiple therapies to provide effective relief that is affordable and convenient for the client while minimizing potential adverse effects.
- For patients with food allergy, emphasize lifelong dietary restriction.
- For patients with atopic dermatitis, recommend allergy testing and immunotherapy (with conventional allergy shots or new sublingual method).
- For patients with atopic or atopic-like dermatitis, implement additional long-term management elements:
- Medicate with cyclosporine A (dog, cat) or oclacitinib (dog).
- Medicate with a topical or systemic corticosteroid (perhaps with an antihistamine to lower required dose).
- Prescribe frequent bathing with appropriate medicated or cleansing shampoo.
- Institute epidermal barrier support, including fatty-acid supplementation and topical methods.
|Clinical Features of Pruritus: A Mental Chalkboard|
Sudden onset? Think parasites.
Gradual onset? Think allergy or infection.
If severe, scabies is a prime consideration.
If seasonal, think flea or environmental allergy (vs food allergy).
If initial itch developed into a rash, primary allergic or parasitic cause with secondary infection is most likely.
If initial presentation was a rash that itched, infectio is most likely.
Ifpruritus responds well to coricosteroid therapy, atopic dermatitis or flea allergy is more likely.
If pruritus responds poorly to coticosteroid therapy, scabies, yeast dermatitis, or food allergy is more likely.
- Comparison of the onset and antipruritic activity of the JAK inhibitor oclacitinib to prednisolone and dexamethasone in an interleukin-31 canine model of pruritus [abstract]. Fleck TJ, Humphrey WH, Galvan BA, et al. Vet Dermatol 24:297, 2013.
- Current understanding of the pathophysiologic mechanisms of canine atopic dermatitis. Marsella R, Sousa CA, Gonzales AJ, Fadok VA. JAVMA 241:194-207, 2012.
- Fixing the skin barrier: Past, present and future —man and dog compared. Marsella R. Vet Dermatol 24:73-76, 2013.
- Treatment of canine atopic dermatitis: 2010 clinical practice guidelines from the international task force on canine atopic dermatitis. Olivry T, DeBoer DJ, Favrot C, et al. Vet Dermatol 21:233-248, 2010.
- A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis. Favrot C, Steffan J, Seewald W, Picco F. Vet Dermatol 21:23-31, 2010.
- A systematic review of randomized controlled trials for prevention or treatment of atopic dermatitis in dogs: 2008-2011 update. Olivry T, Bizikova P. Vet Dermatol 24:97-117, 2013
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