Itchy Dog, Head to Toe, Year Round
by Steven A. Melman, VMD

Summer 2000, NEWS

An 18 month old, 15 pound male West Highland White Terrier named Yancy was presented with a history of year-round facial and pedal pruritus (face rubbing, foot licking and itch), which seemed to be worse in the summer and fall. Previous treatment with corticosteroids and antibiotics partially relieved the problem. Yancy spent some time in a kennel during the family's vacation and was on a premium lamb and rice dog food.

Our physical examination revealed epidermal collarettes in the groin (collar like areas on the skin indicating skin infection) and antecubital (under the forearm) area. We noted there was also evidence of follicular plugging (pustules) and alopecia (hair loss). In addition, Yancy had mild reddening around the muzzle. Otic examination, skin scrapes, and a fungal culture were all unremarkable.

The differential diagnosis was extensive, so rather than trying to pinpoint a specific diagnosis during the first visit, Yancy was placed on a "pruritic clinical trial" (see box at end of this article). The trial is a rapid approach to diagnosis and treatment of the itchy pet that initiates treatment at several different levels simultaneously. The timing of symptom reduction, elimination, or return is the key to the trial, so client compliance and observation are of paramount importance. The owners were asked to keep a journal and grade the itch daily on a scale of 1 to 7, with a 1 being the worst Yancy had ever been; 2, very itchy; 3, itchy; 4, no change; 5, improved; 6, much less itchy; and, 7, not itchy.

We prescribed bathing Yancy twice a week with a chlorhexidine 2% shampoo followed by a chlorhexidine 2% conditioner. Additionally, we prescribed omega-3 and omega-6 fatty acid supplements to be given orally for thirty days. We started Yancy on a strict hypoallergenic diet, with instructions to avoid extra treats not in the diet. Because Yancy had bacterial skin infections, we prescribed an oral antibiotic. Additionally, we prescribed the antihistamine hydroxyzine and the corticosteroid prednisone. We treated potential internal parasites with Drontal and potential external parasites with Ivermectin and Advantage. At this time, we did not have clinical signs of Malassezia yeast infection; therefore, we didn't prescribe ketoconazole and Malacetic shampoo.

Results:

Twenty-one days later, Yancy presented for reexamination. The pyoderma (purulent skin disease) had resolved. According to our clients, the epidermal collarettes and pustules had disappeared at least 10 days before. The itching had improved. Yancy was grading between 6 and 7 until the day when he began to lick his feet, which the owners graded 5. The owners felt that despite the fact that Yancy was still pruritic, he was "comfortably itchy", and did not need to be worked up further for what appeared to be atopy (allergy). After the diet was changed, the itching did not noticeably change, so we eliminated food allergy from the differential.

If itching had stopped during the time when the prednisone and Ivermectin (steps 4 and 6 in the pruritic clinical trial) were given, and it had never returned, then scabies could have been presumably diagnosed. In Yancy's case, the Ivermectin treatment and the prednisone broke the itching cycle. However, his itching returned after the prednisone was stopped, leaving us with the most likely diagnosis of atopy.

Contact allergy could have been possible; however, severe itching should have recurred despite shampoo therapy and fatty-acid supplements. Bacterial hypersensitivity is suspected if the itch returns with a pyoderma (bacterial skin infection) within 30 days of stopping antibiotics. If the itch and the pyoderma disappear after a second course of antibiotics, the diagnosis is confirmed.

Keratinization disorders, psychogenic pruritus, skin cancer, cutaneous infection with Malassezia spp., and other less common primary skin disease may prevent the itch from resolving. Additionally, scabies that resist treatment are perhaps due to a failure of the owner to treat the environment or all animals the patient comes in contact with. A biopsy or cytology may be helpful in diagnosing those conditions. If the itch does not improve at all from the pruritic clinical trial and is not prednisone-responsive, then one should examine the patient closely for Malassezia. While methods such as roll smears have been described, a 10-day trial of ketoconazole with an acetic acid/boric acid shampoo daily can be used to diagnose this condition. If the patient improves, continue to use both agents for 30 days, then use the shampoo only on a weekly basis for 30 days or more.

If the pyoderma does not respond to therapy, then look for acantholytic cells with examination room cytology, culture, blood test and biopsy. Autoimmune disease, such as lupus erythematosus and pemphigus complex, can be pruritic and will not respond to this trial unless they go into a waning period. Recurrent pyoderma is a subject all to itself. However, the basic principle of looking for the underlying disease is important.

Analysis:

This case apparently fell into the category of atopy responsive to shampoo therapy using a hypoallergenic shampoo as often as possible, and fatty acid supplementation. Since food allergy had been eliminated, the use of a palatable, protein-containing fatty acid supplement could be considered. At this point, we continued the prescriptions of an antihistamine (hydroxyzine) and limited amounts of prednisone (corticosteroid). We advised Yancy's owners that if there were further bouts of itching, then Yancy might need to be on hydroxyzine long term. If the hydroxyzine was ineffective, other antihistamines or combination of antihistamines might be required. Additionally, we advised that Yancy might be placed on low dose prednisone. We instructed that if Yancy needed prednisone more than 3 or 4 times, then we needed to consider allergy testing, with the goal of hypo-sensitization. While this method of employing a pruritic clinical trial can be effective with practice, in some cases, one must also consider combinations of diagnoses that may require the trained, interpretive skills of a board-certified veterinary dermatologist.

Pruritic Clinical Trial:

1. Shampoo Therapy: Shampoo daily with a hypoallergenic shampoo. Removal of the offending antigen from the coat is fundamental. If bacterial skin infection is present, use an antibacterial shampoo containing chlorhexidine 2 to 4%, MalAcetic Shampoo or MalAcetic Conditioner. Bathe twice weekly. If itching is severe, then use an oatmeal shampoo instead of the hypoallergenic. After bathing, use a leave-on oatmeal conditioner.
2. Prescribe an omega - 3 and omega - 6 fatty acid supplement, preferably with antioxidants.
3. Follow a strict hypoallergenic diet for 30 days. Home cooked, all vegetable, turkey or lamb diets with rice are preferable. A copy of a home-cooked diet is available in "Food Allergy", a chapter by Kevin Byrne in "Skin Diseases of Dogs and Cats". Available at the Dermapet.com website.
4. Antibiotics are only used if a bacterial skin infection (pyoderma) is present. Antihistamine and prednisone are used to control and eliminate pruritus.
5. Treat phantom endoparasites (worms) with an anthelminthic (de-wormer) that also targets whipworms.
6. Treat ectoparasites (scabies and fleas) using Ivermectin or selamectin for scabies, and begin a flea control program. Since frequent bathing is recommended, a compound that is supposedly not washed off or neutralized by shampooing is preferable. The advent of selamectin (Revolution) affords the clinician a single treatment to eliminate fleas and scabies.
7. Treat Malassezia: MalAcetic Shampoo every other day. Use antibiotics to eliminate concurrent pyoderma and use ketoconazole to eliminate Malassezia.

Reprinted with permission from DermaPet