Think like a dermatologist: untangling itch

During the past decade I’ve treated thousands of pruritic dogs and cats, some with very extreme presentations, and lengthy diagnostic and therapeutic histories. Regardless of how mundane or shocking the presentation, I rely on a steadfast diagnostic foundation to ensure that no diagnoses are missed. My passion is not dogma; rather, it’s the art of communication and tailoring therapy to meet the needs of patients and clients. With these principles firmly in place, I confidently enjoy even the most challenging of cases, placing focus on the client and the patient.

The first thing to keep in mind is that pruritus control, when strategically executed, does not interfere with the diagnosis. Rather, it enhances client adherence and confidence.

Infections and infestations

Look for lesions associated with folliculitis, such as patches of alopecia, papules, pustules, crusts, comedones, or collarettes. If any of these are present, perform multiple deep skin scrapes for Demodex (D canis and injai in dogs, and D cati, albeit rare, in cats). Obtain multiple cytologic preparations to assess for staphylococcal infection. In cats, crusted papules may arise due solely to hypersensitivity, or they may represent staphylococcal infection, so remember to look.

Demodex gatoi, 10x objective

Demodex injai

Consider a dermatophyte culture with or without polymerase chain reaction (for a rapid result), particularly if no Demodex or cocci are found. Should your cytologies, deep skin scrapes, and dermatophyte culture provide no diagnosis, then perform multiple skin biopsies, because your patient may have a less common diagnosis such as pemphigus foliaceus, sebaceous adenitis, or cutaneous lymphoma.

Also examine your patients for nonspecific inflammatory lesions, including patchy erythema, lichenification, and seborrhea. Consider impression smear or acetate cytology to assess for bacterial and/or Malassezia surface overgrowth. Perform deep skin scrapes for Demodex as well as superficial skin scrapes to assess for Cheyletiella, Sarcoptes (dogs), and D gatoi (cats). and D gatoi (cats).

Superficial scrapes do not yield reliable results for 2 pruritogenic mites: Sarcoptes scabiei in dogs and D gatoi in cats. Of note, D gatoi may mimic the classic “fur mowing” presentation of feline hypersensitivity. Diagnosis is frequently made via response to therapy. The isoxazolines work well against both mites.

Flea bite hypersensitivity

Ensure that strict flea control is in place for all dogs and cats in the home. I particularly like the isoxazoline products (eg, Simparica; Zoetis) for parasite prevention.

Staphylococcus and Malassezia

Treat secondary Staphylococcus and Malassezia for a minimum of 2 weeks and recheck the patient during therapy. Infections enhance dermatitis severity and confound interpretation of ectoparasite control and elimination diet trials. Once infections are resolved, if you are pursuing a diet trial or have diagnosed the patient with atopic dermatitis (environmental allergy), consider preventive maintenance topical therapy at least twice weekly in key areas of recurrent secondary infection (eg, miconazole and chlorhexidine wipes on the interdigital spaces).

Food allergy and atopic dermatitis

Food allergy is diagnosed via an 8-week elimination diet trial, and atopic dermatitis is a diagnosis of exclusion. Allergy testing for the diagnosis of atopic dermatitis, whether intradermal or serologic, is not reliable because false positives do occur. I use these tests solely to identify allergens for inclusion in immunotherapy. If you have performed your baseline diagnostics and are still unsure about the diagnosis, consider referral to a dermatologist.

Treatment options

Canine itch relief

Rapid and reliable canine itch relief options include oclacitinib (Apoquel; Zoetis), lokivetmab (Cytopoint; Zoetis), and systemic corticosteroids (eg, oral prednisolone). Oclacitinib and lokivetmab are well tolerated and efficacious, and do not require a washout period or discontinuation for allergy testing. Treatment is chosen based on patient factors and client preference. For patients aged less than 1 year, I prescribe lokivetmab. It is prudent to rule out demodicosis prior to prescribing oclacitinib or corticosteroids.

Canine chronic atopic dermatitis

Rapid and reliable chronic atopic dermatitis options for dogs include lokivetmab, oclacitinib, modified cyclosporine (Atopica; Elanco), and allergenspecific immunotherapy. Immunotherapy can take up to a year to provide noticeable benefit, so I invariably initiate immunotherapy with concurrent antipruritic therapy. If corticosteroids must be used, try to reduce the dose to the lowest every-other-day dose possible to reduce adverse effects, such as calcinosis cutis.

Pyogranulomatous inflammation with predominantly extracellular cocci. Impression smear, 100x objective

Malassezia. Acetate tape preparation, 100x objective

Feline itch relief

Rapid and reliable itch relief options for cats include systemic corticosteroids (eg, oral prednisolone, dexamethasone) and oclacitinib. Of note, although oclacitinib is not approved in cats, recent studies support its efficacy^1,2 in feline hypersensitivity, as well as its safety³ and bioavailability⁴ in cats. A recent pharmacokinetic study⁴ supports a more frequent and higher dosing schedule in cats compared with dogs. Doses documented include 0.4 to 2 mg/kg every 12 to 24 hours.^1,2 The 2-mg/kg dose has been associated with gastrointestinal upset.³ I typically start at 0.5 to 1.0 mg/kg twice daily for 1 to 2 weeks followed by daily therapy. It has been well tolerated in my patients. Long-term tablet therapy may prove difficult for clients and their cats.

Chronic atopic dermatitis in cats

Treatment options for chronic atopic dermatitis in cats include cyclosporine, allergen-specific cyclosporine, and allergen specific immunotherapy. With regard to the safety of oclacitinib in cats, information is limited to 3 studies, all spanning a period of 28 days.^1-4 Therefore, it is prudent to consider baseline complete blood cell count, chemistry, and urinalysis findings and repeat these tests every 3 to 6 months initially, and in otherwise healthy patients perhaps consider at least annual monitoring. As with dogs, if long-term corticosteroids are used in cats, use the lowest every-other-day dose required to provide acceptable relief.

Moderately to severely affected dogs will require maintenance administration of 1 of these therapies for good control. The addition of weekly bathing with a moisturizing shampoo, daily fatty acid therapy, and topical antimicrobials and barrier restoring (eg, phytosphingosine) optimizes control. Even with consistent treatment, breakthrough itch will occur periodically occur and may prompt temporary or longer term changes in therapy.

What about antihistamines?

Antihistamines provide lackluster results, so I do not recommend them for acute pruritus. Chronic administration of antihistamines as an adjunct immunotherapy and/or fatty acid regimen may help reduce pruritus and have a steroids paring effect. Studies regarding pharmacokinetics and efficacy of antihistamines are relatively few. The most evidence based in the dog are hydroxyzine and chlorpheniramine.⁵

References

1. Ortalda C, Noli C, Colombo S, Borio S. Oclacitinib in feline nonflea-, nonfood-induced hypersensitivity dermatitis: results of a small prospective pilot study of client-owned cats. Vet Dermatol. 2015;26(4)
2. Noli C, Matricoti I, Schievano C. A double-blinded, randomized, methylprednisolone-controlled study on the efficacy of oclacitinib in the management of pruritus in cats with nonflea nonfood-induced hypersensitivity dermatitis. Vet Dermatol. 2019;30(2):110-e30. doi:10.1111/ vde.12720
3. Lopes NL, Campos DR, Machado MA, et al. A blinded, randomized, placebo-controlled trial of the safety of oclacitinib in cats. BMC Vet Res. 2019;15(1):137. doi:10.1186/ s12917-019-1893-x
4. Ferrer L, Carrasco I, Cristòfol C, Puigdemont A. A pharmacokinetic study of oclacitinib maleate in six cats. Vet Dermatol. 2020;31(2):134- 137. doi:10.1111/vde.12819
5. Eichenseer M, Johansen C, Mueller RS. Efficacy of dimetinden and hydroxyzine/chlorpheniramine in atopic dogs: a randomised, controlled, double-blinded trial. Vet Rec. 2013;173(17):423. doi:10.1136/ vr.101907