Executive Summary and Introduction

Canine Atopic Dermatitis (CAD) stands as one of the most prevalent and clinically challenging inflammatory skin diseases managed in veterinary practice. A significant and often frustrating comorbidity of CAD is recurrent otitis externa (OE), an inflammatory condition of the external ear canal that frequently persists despite standard-of-care treatments for the underlying allergic disease. This chronicity leads to significant patient discomfort, client distress, and a substantial financial and emotional burden. The cyclical nature of treatment, remission, and relapse underscores a critical need for proactive, foundational management strategies that can extend periods of remission and reduce the reliance on pharmaceuticals, particularly antimicrobials and corticosteroids.

In response to this clinical need, a landmark 6-month, multicenter, randomized, double-blind, placebo-controlled clinical trial was conducted by Watson et al. to investigate the efficacy of a targeted therapeutic diet. The study aimed to determine if a diet formulated with specific active ingredients designed to support the skin barrier and modulate allergic inflammatory pathways could reduce the incidence rate of OE episodes in dogs with diagnosed CAD. The findings, published in Veterinary Dermatology, provide compelling evidence for a paradigm shift in the multimodal management of CAD. The study conclusively demonstrates that the therapeutic diet, known as Skintopic, reduces the incidence rate of OE episodes by more than half (25% in the test group vs. 61.1% in the control group; p < 0.01) and provides a significant medication-sparing effect. This document provides an exhaustive summary of this pivotal study, detailing its methodology, key results, and profound clinical implications for veterinary practitioners.

Detailed Materials and Methods

The credibility and strength of the study’s conclusions are founded on its robust and rigorous methodological design, which adhered to the gold standard of clinical research.

1. Study Design and Population

The trial was a 6-month, parallel-design, multicenter, randomized, double-blind, and placebo-controlled study conducted across several veterinary dermatology referral clinics in Europe. A total of 42 client-owned dogs were initially enrolled, with 34 ultimately qualifying for the efficacy analysis.

Inclusion Criteria: To be eligible, dogs had to have a confirmed diagnosis of non-food-induced CAD, satisfying at least five of the eight Favrot’s Criteria. A crucial requirement was the presence of active, unilateral or bilateral, erythro-ceruminous otitis externa, quantified by an Otitis Index Score (OTIS-3) greater than 4 for each affected ear. Additionally, dogs had to exhibit a significant level of itching, confirmed by an owner-assessed pruritus Visual Analog Scale (PVAS) score greater than 3 out of 10. A prior diagnostic exclusion of food-induced atopic dermatitis via a strict elimination diet and subsequent rechallenge was mandatory.

Exclusion Criteria: Dogs were excluded if they presented with otitis media, a ruptured tympanic membrane, or any form of food allergy. A critical exclusion was the presence of bacterial rods or a Pseudomonas infection in the initial ear cytology, to ensure the study focused on the typical cocci and yeast overgrowth associated with allergic otitis. Dogs that had recently started allergen-specific immunotherapy (less than 6 months prior) or were not under strict ectoparasite control were also excluded.

2. Interventions: Diets and Medical Protocol

Study Diets: The 34 dogs were randomly assigned to one of two groups. The Test Group (n=16) received the therapeutic diet (Skintopic), a dry kibble specifically formulated to support skin health. The Control Group (n=18) received a control diet, also a chicken-based dry kibble, designed to be similar in physical appearance and palatability but lacking the specific active ingredients of the test diet. Both owners and investigators were blinded to the diet assignments. The key nutritional differences included significantly higher levels in the test diet of: Linoleic acid (4.10% vs. 2.15%), EPA & DHA (0.6% vs. 0.07%), Vitamin E (900 mg/kg vs. 165 mg/kg), and Taurine (4400 mg/kg vs. 600 mg/kg). The test diet was also uniquely supplemented with a curcuma extract (1250 mg/kg) and a licorice root extract (480 mg/kg), which were absent in the control diet.

Standardized Medical Protocol: To ensure a consistent baseline, all dogs upon enrollment began a standardized 10-day induction therapy to bring the active OE into remission. This consisted of a topical combination product (hydrocortisone aceponate, miconazole, gentamicin) administered daily, alongside oral prednisolone (0.5 mg/kg once daily). To prevent early relapse, this was followed by a twice-weekly application of a topical hydrocortisone spray until the Month 1 visit. A dog could only continue in the study if their OTIS-3 score was less than 4 at the Month 1 recheck, confirming remission had been successfully achieved and maintained.

Any subsequent relapse of OE during the 6-month study was managed with the same 10-day induction protocol. The use of other immunomodulatory drugs (such as ciclosporin, oclacitinib, or lokivetmab) to control systemic CAD was permitted at the discretion of the clinician, with the goal of reducing their use whenever clinically appropriate.

3. Outcome Measures and Assessment

A comprehensive set of validated scoring systems was used to objectively assess the outcomes.

• Primary Outcome: The primary measure of success was the incidence rate of OE, defined as the percentage of dogs in each group that experienced one or more relapses of otitis after achieving remission at Month 1.
• Secondary Outcomes:
  • Time to First Relapse: The duration, in months, until the first OE episode occurred.
  • OTIS-3 (Otitis Index Score): A clinician-assessed score evaluating erythema, edema, erosion, and exudate in the ear canals.
  • CADESI-04 (Canine Atopic Dermatitis Extent and Severity Index): A clinician-assessed score measuring the severity of skin lesions across the body.
  • PVAS (Pruritus Visual Analog Scale): An owner-assessed score from 0 to 10 measuring the dog’s overall level of itchiness.
  • Medication Score: A composite score quantifying the daily burden of all medications (topical and systemic) required to control both OE and CAD. A higher score indicated a greater reliance on pharmaceuticals.

Exhaustive Review of Study Results

The data collected over the six-month period revealed statistically significant and clinically meaningful differences between the two diet groups.

1. Primary Outcome: A Drastic Reduction in Otitis Externa Relapse

The most important finding of the study related to its primary objective. The incidence rate of OE relapse was significantly lower in the test group compared to the control group. Only 25.0% (4 out of 16) of dogs fed the Skintopic diet experienced a relapse of otitis externa during the 6-month trial. In stark contrast, 61.1% (11 out of 18) of dogs on the control diet had a relapse (p < 0.01). This result indicates that the therapeutic diet more than halved the likelihood of an otitis flare-up in this atopic dog population. Furthermore, the median time to the first episode was significantly longer in the test group (7 months, imputed for non-relapsers) compared to the control group (5 months; p=0.031), demonstrating that the diet not only prevented flares but also delayed them when they did occur.

2. Secondary Outcomes: Sustained Improvement vs. Rebound Effect

The trajectories of the secondary scores told a compelling story. Following the initial medical protocol, both groups showed significant improvement in their clinical scores (OTIS-3, CADESI-04, and PVAS) by the Month 3 visit, which was expected. However, the critical difference emerged between Month 3 and the study’s end-point.

OTIS-3 and CADESI-04 Scores: In the control group, both the otitis score (OTIS-3) and the general dermatitis score (CADESI-04) showed a statistically significant rebound effect after Month 3, increasing back towards their baseline levels. This suggests that without the supportive effect of the diet, the benefits of the initial medical therapy waned quickly. Conversely, in the test group, while there was a slight increase in these scores, it was not statistically significant. The improvement gained from the initial therapy was better sustained in the dogs receiving the therapeutic diet.

PVAS (Pruritus) Score: A similar pattern was observed with the owner-assessed itch scores. While both groups were significantly less itchy at Month 3, only the test group maintained this significant improvement through to the end of the study (p=0.001 compared to baseline). The control group’s pruritus score increased significantly between Month 3 and the end-point, returning to a level not significantly different from their original baseline itch.

3. Medication Score: A Powerful Medication-Sparing Effect

Perhaps one of the most clinically relevant findings was the impact on medication usage. In the test group, the medication score decreased dramatically and significantly from baseline to Month 3 (p < 0.0001) and remained significantly low through to the end of the study. This demonstrates a powerful and sustained medication-sparing effect. In contrast, the control group showed no significant change in their medication score at any point during the study. They required a consistent, high level of medication throughout the 6 months to manage their condition, whereas the dogs on the therapeutic diet required progressively less pharmacological intervention.

Discussion and Clinical Implications

The findings of the Watson et al. study have profound implications for the long-term management of canine atopic dermatitis and its associated otitis externa.

Interpretation of Findings: The study clearly demonstrates that while initial medical therapy is essential for inducing remission of acute OE, a targeted therapeutic diet plays a crucial role in maintaining that remission and preventing the common cycle of relapse. The diet acts as a foundational, proactive strategy that works synergistically with conventional therapies. The significant medication-sparing effect is of paramount importance, as it can help reduce the potential long-term side effects associated with immunosuppressive drugs and corticosteroids, decrease the cost of care for the owner, and support antimicrobial stewardship efforts.

Study Limitations: The authors transparently acknowledged several limitations inherent in a field study, including the inability to perform an initial diet washout period, a study duration that, while long, may not capture full seasonality, and a baseline difference in average age between the two groups. However, the robust, blinded, and controlled nature of the study design ensures that these limitations do not detract from the validity of the primary conclusions.