Otto loses his pants Otto was miserable. The once-confident cat had turned into a shadow of himself, hiding under the bed and licking his belly and back legs bald (Figure 1). Fortunately, his owner and primary care veterinarian did not assume he was stressed but instead partnered with a dermatology specialist to diagnose and manage feline atopic skin syndrome (FASS). As our understanding of the clinical signs and treatment of this disease has advanced, it is time to sharpen our approach to these cases and give cats like Otto the relief they desperately need. Figure 1. Introduction In February of 2021, the International Committee on Allergic Diseases of Animals (ICADA) Cat Team proposed guidelines for understanding clinical signs, developing a diagnostic plan, and implementing treatment for cats with feline atopic syndrome (FAS).1,2 FAS refers to the spectrum of feline hypersensitivity disorders of the gastrointestinal tract, respiratory tract, and skin. FASS refers specifically to cutaneous reaction patterns. Allergic cats do not present with the same predictable signs that allergic dogs may develop, and FASS reaction patterns can mimic other common diseases. This discussion will help familiarize you with the common reaction patterns, important differentials to rule out, and therapeutic options, including risks and benefits to consider. Cutaneous reaction patterns The four main reaction patterns associated with FAS are: 1) Miliary dermatitis (MD) MD involves the development of crusts 1-2 mm in size that can develop anywhere on the body, frequently dorsally (Figure 2). These cats may have pruritic excoriations most of the time. Other times, they appear nonpruritic, and pinpoint crusts only become apparent on good palpation, emphasizing the importance of a low-stress environment for examinations. Figure 2., Miliary dermatitis on the dorsum of a cat with FASS. Photo courtesy Dr. Brittany Lancellotti 2) Self-inflicted alopecia/hypotrichosis (SIAH) SIAH results from excessive licking, scratching, “corncobbing,” and chewing (Figures 3 and 4). Hair may be mixed in with regurgitated ingesta and feces. Pet owners may or may not witness overgrooming behaviors. Stress and behavior-related overgrooming are possible but are commonly overdiagnosed when there is actual allergic disease.3 A thorough workup of FASS is recommended for cats with SIAH. Figure 3. Self-induced alopecia and hypotrichosis with erosion from severe overgrooming on the ventral abdomen of a cat with FASS. Photo courtesy Dr. Brittany Lancellotti Figure 4. Alopecia to the ventral abdomen of a cat with FASS. Photo courtesy Dr. Brittany Lancellotti 3) Head and neck pruritus (HNP) HNP is an intense itch focused around the face and cervical regions (Figures 5 and 6). Cats with this condition are miserable, clawing at their heads until they are bleeding, raw, and secondarily infected. These animals often need physical barriers, such as e-collars, to prevent severe self-trauma. Secondary ocular lesions, such as blepharitis and corneal ulcers, may occur. Figure 5. Alopecia, lichenification, excoriations, and secondary infection to the ventral cervical skin in a cat with severe head and neck pruritus. Photo courtesy Dr. Brittany Lancellotti Figure 6. Erythema of the preauricular skin with hypotrichosis to the dorsal caudal muzzle in a cat with head and neck pruritus. Photo courtesy Dr. Brittany Lancellotti 4) Eosinophilic granuloma complex (ECG), including: Indolent ulcer Linear granuloma Eosinophilic plaque ECG complex is a group of syndromes involving a reaction pattern caused by dysfunction of eosinophils, commonly involved in FAS (Figure 7). Indolent ulcers are also referred to as “rodent ulcers,” most often appear as edema and ulceration of the rostral maxillary lips. Ulcers typically begin unilaterally, then become bilateral. Chronicity and severity may affect the rostral nasal planum and lead to scaring. Infection is common; cytology should be performed, and intracellular bacteria should be addressed with appropriate antimicrobial therapy with concurrent anti-inflammatories. Squamous cell carcinoma should be considered as a differential, and a biopsy can be considered. Figure 7. Eosinophilic granuloma presentations associated with FASS, including from left to right 1) indolent ulcer/rodent ulcer, 2) linear granuloma, and 3) eosinophilic plaque. Photo courtesy Dr. Brittany Lancellotti Linear granulomas are lines of thickened skin that can be ulcerated, most often on the back of the thighs, with or without pruritus. Oral exams should be performed to evaluate granulomas on the soft palate and the tongue. Chin edema is considered a form of a linear granuloma (Figure 8). Figure 8. “Fat chin” is a form of linear granuloma that can be seen in cats with FASS. Photo courtesy Dr. Brittany Lancellotti Eosinophilic plaque varies in shape, including circular, oval, or serpiginous, occurring anywhere on the body, most frequently on the ventral abdomen or medial thighs. These intensely pruritic lesions are often complicated by secondary infection. Allergic gastrointestinal and respiratory disease Feline hypersensitivity disorders may occur within the gastrointestinal and respiratory tracts with or without FASS. Cutaneous manifestations of feline food allergy are identical to FASS, and an eight- to 12-week elimination diet trial using a prescription hydrolyzed or novel protein diet, depending on what the cat will tolerate, will help eliminate clinical signs stemming from food. Feline asthma is a common Type-1 bronchial hypersensitivity disorder leading to dyspnea, open-mouth breathing, expiratory wheezing, chronic cough, and exercise intolerance. Coughing may be confused by owners as unproductive attempts at hairballs. Thoracic imaging with radiographs, airway sampling through bronchoalveolar lavage, and parasite testing for heartworm and lungworm can rule out common asthma mimickers, including chronic bronchitis, cardiomyopathy, neoplasia, and infectious disease. Testing to rule out important differentials FASS is a diagnosis of exclusion, necessitating a thorough workup and rule out of important differentials, including ectoparasites (fleas, mites, and lice), food allergies, and infections (both primary, such as dermatophyte and viral, as well as secondary, such as Staphylococcus sp. and Malassezia). Superficial and deep skin scrapes can identify ectoparasites (Demodex gatoi or cati, Notoedres, Cheyletiella and Lynxacarus). Evaluation of ear debris with mineral oil can reveal copious Otodectes. A fecal exam can occasionally be used to identify mites. Because parasites may sometimes be difficult to observe, such as the intensely pruritic D. gatoi, a parasite treatment trial is important to perform. Flea allergy dermatitis is an important differential that benefits from a well-performed parasite prevention plan and can occur concurrently with FASS. Empiric treatment should be implemented with a prescription adulticidal +/—larvicidal, depending on the speed of kill of the adulticidal. UV-stable Pyriproxifen can be applied outdoors, and aggressive vacuuming indoors will help minimize the length of any ongoing infestation. Bacterial and yeast overgrowth are common, especially when the skin barrier is damaged. Cytology is recommended to direct systemic or topical antimicrobial therapy. Management of secondary infections can help lower the need for anti-inflammatory medications. As mentioned earlier, an eight- to 12-week elimination diet trial should be performed to determine if there are persistent clinical signs to suggest FASS. If all other differentials are ruled out, allergy testing can be considered to formulate allergy-specific immunotherapy. Intradermal allergy testing detects the presence of allergen-specific IgE bound to mast cells, and serum testing measures circulating IgE, but can have false positives and negatives. Allergen testing is recommended to be performed by veterinarian dermatologists if regionally available, as increased compliance with starting and refilling immunotherapy is seen when formulated and managed by dermatologists compared to general practitioners.4 Treatment of feline atopic syndrome Treatment of FAS should be tailored to the individual animal, taking into consideration lesion severity, comorbidities, temperament, and other factors. More data is needed, and referral to dermatology specialists is recommended to include patients in ongoing studies. No studies have evaluated allergen avoidance specifically for FASS. One cat with asthma triggered by human dander improved by restricting access to the bedroom. Two cats with storage mite-induced asthma resolved by switching from dry kibble to wet food. Allergen immunotherapy has more data for FASS and appears to be efficacious for both cutaneous and respiratory allergic disease (Figures 9 and 10).2,5 Before and after of a cat with severe head and neck pruritus managed with allergy-specific immunotherapy alone without the need for additional symptomatic anti-inflammatory medications. Photos courtesy Dr. Brittany Lancellotti Glucocorticoids are rapid-acting and are efficacious for both FASS. Injectable steroids are not indicated for chronic management due to increased risks. Complete blood count and serum chemistry should be regularly monitored for changes, such as hyperglycemia and elevated liver and kidney values, which are commonly seen. Methylprednisolone and triamcinolone are reported to be more effective than prednisolone.6 Hydrocortisone aceponate was shown to be effective for FASS in one study, but more long-term data and FDA-approved options are needed.7 There is good evidence for the use of inhaled glucocorticoids for asthma.5 Modified cyclosporine (Atopica, Elanco) was effective in 40-100 percent of 328 cats evaluated across nine studies with varying study designs.5,8 Cyclosporine may take four weeks to start working. Adverse effects, such as gastrointestinal upset, gingival hyperplasia, and more severe clinical signs with Toxoplasma gondii infection, can be seen. In one study of 157 cats, about 60 percent were maintained with twice-weekly dosing; 15-20 percent were maintained on every-other-day dosing, and only 15 percent were maintained on daily dosing, which helps improve client compliance and quality of life.9 Oclacitinib (Apoquel, Zoetis) was evaluated in a few short-term studies with limited numbers of cats.2,10 About 30-50 percent of cats had a good response within one month of starting. Data suggest effective dosing may need to be higher and more frequent than dosing used for dogs.10,11 Neutropenia, thrombocytopenia, elevated kidney values, and ALT were reported. Fatal toxoplasmosis was reported in one FIV+ cat.12 Off-label use of oclacitinib for FASS or feline asthma is not currently recommended as first-line treatment, as significantly more data is needed, and other FDA-approved options are available. Antihistamines are unlikely to provide a good response but may provide a partial response in early or mild FASS. Antihistamines do not decrease inflammatory cytokines in asthmatic cats. Prophylactic use can be considered to prevent flares once clinical signs are controlled, but it is likely to be unable to resolve acute flares as a monotherapy. Similar data suggest essential fatty acids (EFAs) and palmitoylethanolamide (PEAum) can provide some benefit in early/mild FASS but there is insufficient evidence to recommend their use for asthma.2 Conclusion Cats with allergic skin disease are some of our most misunderstood patients, and they deserve more than a dismissive label of “overgrooming from stress.” Communication strategies, such as providing owners with educational tools (See: “Listening materials”), can improve understanding of and compliance with recommendations. Listening materials Check out Episodes 70-72 of the Your Vet Wants You to Know podcast for more information on clinical signs, testing, and treatment of allergies in cats. With a thoughtful diagnostic approach and informed treatment strategies, you are equipped to dramatically improve the quality of life for both your feline patients and their families (Figure 11). Do not underestimate the impact of your expertise—lean into the workup, partner with dermatology when needed, and be the advocate these itchy, miserable cats need. The difference you make starts with a closer look. Figure 11. Full hair regrowth is seen on Otto’s legs after implementing immunotherapy to desensitize him to his environmental allergens. Photo courtesy Dr. Brittany Lancellotti Brittany Lancellotti, DVM, DACVD, is the founder and host of Your Vet Wants You to Know, practices at Veterinary Skin and Ear in Los Angeles, Calif., and is a Fear Free-certified practitioner. Dr. Lancellotti graduated with honors from WesternU, enjoys teaching nationally, internationally, and virtually, and loves playing the piano. References Santoro, Domenico, Cherie M. Pucheu-Haston, Christine Prost, Ralf S. Mueller, and Hilary Jackson. 2021. ‘Clinical Signs and Diagnosis of Feline Atopic Syndrome: Detailed Guidelines for a Correct Diagnosis’. Veterinary Dermatology. Blackwell Publishing Ltd. https://doi.org/10.1111/vde.12935. Mueller, Ralf S., Tim Nuttall, Christine Prost, Bianka Schulz, and Petra Bizikova. 2021. ‘Treatment of the Feline Atopic Syndrome – a Systematic Review’. Veterinary Dermatology. Blackwell Publishing Ltd. https://doi.org/10.1111/vde.12933. Waisglass, Stephen E, Gary M Landsberg, Julie A Yager, and Jan A Hall. 2006. ‘Underlying Medical Conditions in Cats with Presumptive Psychogenic Alopecia’. Journal of the American Veterinary Medical Association 228 (11): 1705–9. https://doi.org/10.2460/javma.228.11.1705. Tater, Kathy Chu, William Elliott Cole, and Paul David Pion. 2017. ‘Allergen-Specific Immunotherapy Prescription Patterns in Veterinary Practice: A US Population-Based Cohort Study’. Veterinary Dermatology 28 (4): 362-e82. https://doi.org/https://doi.org/10.1111/vde.12426. Prost, C. 2004. ‘P-45 Treatment of Allergic Feline Asthma with Allergen Avoidance and Specific Immunotherapy: 20 Cats’. Veterinary Dermatology 15 (s1): 55. https://doi.org/https://doi.org/10.1111/j.1365-3164.2004.00414_45.x. Ganz, Eva C., Craig E. Griffin, Deborah A. Keys, and Tami A. Flatgard. 2012. ‘Evaluation of Methylprednisolone and Triamcinolone for the Induction and Maintenance Treatment of Pruritus in Allergic Cats: A Double-Blinded, Randomized, Prospective Study’. Veterinary Dermatology 23 (5). https://doi.org/10.1111/j.1365-3164.2012.01058. Schmidt, Vanessa, Laura M Buckley, Neil A McEwan, Christophe A Rème, and Tim J Nuttall. 2012. ‘Efficacy of a 0.0584% Hydrocortisone Aceponate Spray in Presumed Feline Allergic Dermatitis: An Open Label Pilot Study’. Veterinary Dermatology 23 (1): 11-e4. https://doi.org/https://doi.org/10.1111/j.1365-3164.2011.00993. Roberts, Elizabeth S, Cindy Speranza, Cecilia Friberg, Craig Griffin, Jean Steffan, Linda Roycroft, and Stephen King. 2016. ‘Confirmatory Field Study for the Evaluation of Ciclosporin at a Target Dose of 7.0 Mg/Kg (3.2 Mg/Lb) in the Control of Feline Hypersensitivity Dermatitis’. Journal of Feline Medicine and Surgery 18 (11): 889–97. https://doi.org/10.1177/1098612X16636660. Roberts, Elizabeth S, Tiffany Tapp, Ann Trimmer, Linda Roycroft, and Stephen King. 2016. ‘Clinical Efficacy and Safety Following Dose Tapering of Ciclosporin in Cats with Hypersensitivity Dermatitis’. Journal of Feline Medicine and Surgery 18 (11): 898–905. https://doi.org/10.1177/1098612X15602523. Carrasco, Isaac, Lluis Ferrer, and Anna Puigdemont. 2022. ‘Efficacy of Oclacitinib for the Control of Feline Atopic Skin Syndrome: Correlating Plasma Concentrations with Clinical Response’. Journal of Feline Medicine and Surgery 24 (8): 787–93. https://doi.org/10.1177/1098612X211048458. Wehber, M, M.C. Eisenschenk, A.J. Young, and S.N. Koch. 2025. ‘2025 Selected Abstracts for NAVDF’. Veterinary Dermatology n/a (n/a): 6. https://doi.org/https://doi.org/10.1111/vde.13359. Moore, Alexandra, Amanda K Burrows, Richard Malik, Rudayna M. Ghubash, Robert D Last, and Benjamin Remaj. 2022. ‘Fatal Disseminated Toxoplasmosis in a Feline Immunodeficiency Virus-Positive Cat Receiving Oclacitinib for Feline Atopic Skin Syndrome’. Veterinary Dermatology 33 (5): 435–39. https://doi.org/https://doi.org/10.1111/vde.13097.
