FELINE atopy is a type 1 hypersensitivity disease caused by environmental allergens. It is relatively uncommon, accounting for less than 5% of the author’s caseload.
No lesion can be said to be pathognomonic for feline atopy, although in a series of cases investigated by Favrot and others (2011) there was a significant correlation with ventral lesions, symmetrical alopecia or a dominant pattern of eosinophilic lesions.
The same authors were unable to uncover a set of criteria that separated cats with non-flea, non-food hypersensitivity from those with food hypersensitivity.
They conclude that the role of food as a cause of non-seasonal pruritus should always be taken into account and properly assessed.
In the authors’ series, atopy was seasonal or non-seasonal and various cutaneous reaction patterns were observed. These were head and neck pruritus, ventral abdomen miliary dermatitis and/or alopecia, miliary dermatitis in other areas (although not dorsally), lesions occurring on caudal thighs and lateral thorax.
Excessive grooming resulted in symmetrical alopecia most commonly, but also miliary dermatitis and lesions of the eosinophilic granuloma complex. In this series it was not possible to diagnose atopy on the basis of the lesion type and site. Diagnosis was made by a step-by-step process ruling out differentials.
Differential diagnosis
The following can be considered as differential diagnoses to feline atopy:
- Flea-bite hypersensitivity.
- Food hypersensitivity.
- Mosquito bite hypersensitivity.
- Ectoparasites (Cheyletiella, Otodectes, Sarcoptes var canis, Notoedres cati, Demodex spp). Of these Notoedres is not currently present in the UK, and Sarcoptes and Demodex are both rarely diagnosed.
- Pyoderma. Rarely a cause but may be implicated in some cases of indolent ulcer.
- Dermatophytosis.
- Psychogenic alopecia.
- Pemphigus foliaceus.
- Epitheliotropic lymphoma.
Diagnosis
- A comprehensive flea control programme is an essential starting point in all cases. This should be tailored to the individual and ability of the client to comply. It is advisable to monitor flea control compliance. carefully throughout the diagnostic process.
- Tape strips to rule out other ectoparasites. Depending on the product used, the flea control programme may also serve to eliminate ectoparasites from the differential diagnosis.
- Cytology to rule out bacteria.
- Culture to rule out dermatophytosis.
- A six- to eight-week hypoallergenic diet (home cooked or commercial) to investigate food allergy.
Biopsy for histopathological examination is not considered useful for the diagnosis of atopy. The results are usually of a non- specific inflammatory nature. Neither intradermal testing nor serological testing for allergens is of value for diagnosis. Either of these tests may be used if immunotherapy is to be tried as treatment.
Intradermal testing is more challenging than in the dog, with reactions being quite subtle. It is usually undertaken in specialist centres.
Improvement with immunotherapy may take up to a year in some cases (Hnilica, 2011), is not guaranteed and thus is not to be undertaken lightly without a full discussion with the owner.
One study (Halliwell, 1997) reports comparable efficacy with the procedure in dogs, using in vitro testing for IgE. Trimmer and others (2006) reported success rates for feline immunotherapy at between 60 and 78%.
Clinical management
- Immunotherapy as outlined above.
- A three-week course of antibiotics such as cephalexin or potentiated clavulanic acid potentiated amoxicillin if cytology demonstrates the presence of bacteria.
- Antihistamines. These have been of limited value in the author’s experience but Hnilica (2011) has reported reduction of clinical signs in between 40 and 70% of atopic cats. The two most favoured treatments described are Chlorpheniramine (2 4mg/cat every 12-24 hours), and Amitriptyline (5-10mg/cat every 12-24 hours).
- Similarly the same author suggests oral essential fatty acid supplements may help reduce clinical signs in 20-50% of cats and reduce glucocorticoid doses.
- Systemic glucocorticoids are extremely effective. Prednisolone 1mg/kg every 24 hours is given initially for two to four weeks until signs resolve, then given at a decreasing alternate day dose until the minimum dose is achieved that maintains the cat in remission. Manycasescanbecontrolled with a dose of prednisolone between 0.5-1mg/kg every 48 hours. A few cases that do not respond adequately to prednisolone may respond to dexamethasone given at a dose of 2mg per cat every 24 hours until remission then tapering to the lowest possible alternate day dose.
- The problem with glucocorticoids is the possibility of side-effects, particularly diabetes mellitus, and the consequent need for careful monitoring, preferably every two months and life-long. Side-effects are much more likely if prednisolone is given every day, which some clients may elect to do without the veterinarian’s knowledge, or particularly with repositol steroid injections. These have no place in the management of feline atopy except in seasons lasting a few months only, and only if the owner has difficulty administering oral medications.
- Cyclosporine (Atopica). This drug is licensed for cats and conveniently packaged as a liquid facilitating easier administration. The dose is 7.5mg/kg every 24 hours until remission of clinical signs and thereafter every 48-72 hours. Cats should be FIV- and FeLv-negative. There is also a risk of toxoplasmosis infection. This appears to be small and can be further reduced by not feeding raw meat and having a collar with two bells to reduce success in those cats that hunt.
References and further reading
- Hnilica, K. A. In: Small Animal Dermatology. A Color Atlas and Therapeutic Guide, 3rd edition; pp198-200. Elsevier, 2011.
- Favrot, C., Steffan, J., Seewald W. et al (2012) Establishment of diagnostic criteria for feline non flea-induced hypersensitivity dermatitis. Veterinary Dermatology 23 (1): 45-e11.
- Halliwell, R. E. W. (1997) Efficacy of hyposensitisation in feline allergic disease based on results of in-vitro testing for allergen specific immunoglobulins. J. Am. Anim. Hosp. Assoc. 23 (3).
- Trimmer, A. M., Grif n, C. E. and Rosenkrantz, W. S. (2006) Feline Immunotherapy 21 (3): 157-161.
