Aproximación Práctica al Gato Con Dermatitis Atópica y Allergias

Clinical Manifestation

Allergic cats present with pruritus that manifest as self-inflicted lesions in the same anatomical areas subject to grooming. Moreover, one or combination of the following reaction patterns are usually present:

 Miliar dermatitis

 Head and/neck pruritus

 Papulo-nodular dermatitis (eosinophilic granuloma complex)

 Autoinduced alopecia (symmetrical or not)

This dermatological problems are not specific of an allergic dermatitis. In fact, they may be occasionally observed in cats with dermatophytosis, bacterial folliculitis, demodicosis, otocariasis, behavioural problems, viral infections and neoplasias. Moreover, they are not suggestive of the allergic disease.

Diagnostic-Therapeutic Protocol

The definitive diagnosis of an allergic dermatitis is based on the exclusion of any non-allergic disease. As the first step, it is necessary to perform a systematic approach in order to exclude all non-allergic disease include in the differential diagnosis, even if considered less probable.

Recently, the Dermatology Department at the University of Zurich has developed criteria for the diagnosis of non-flea hypersensitivity. These criteria must not be considered a replacement for a proper work-up but, rather, tools to evaluate the probability of non-flea hypersensitivity dermatitis before this work-up or to confirm a suspicion thereafter. This work-up will include skin scrapings, microscopic examinations of plucked hairs, scales and otic secretions and Wood lamp examination. It must be considered, in an individual basis, to perform mycological cultures or even skin biopsies to rule out dermatophytosis or less common diseases such pemphigus foliaceus, or herpesvirus dermatitis, for instance. Once non-allergic diseases have been rule out, it is necessary to study the role of cutaneous infections (bacterial and/or Malassezia) on the presumable allergic pruritus through cytological examinations and response to specific antimicrobial treatments.

Thereafter, the allergic protocol starts. Initially, an insecticide and acaricide treatment is set up for a 30–40 days period. If a good clinical response is observed, a parasitic disease and/or flea hypersensitivity is diagnosed. However, a spontaneous resolution should be considered as well.

An elimination diet with hydrolysed diets or homemade diet with a novel protein is made for at least 8 weeks in all those cases where the anti-parasitic treatment does not produce any effect. If a good clinical response is observed, a provocative test (7–10 days) with the habitual diet is perform in order to demonstrate the beneficial effect of the food trial. However, if a favorable response is not observed or the pruritus does not reoccur after provocative trial (spontaneous resolution), a non-flea non-food hypersensitivity is diagnosed.

The role of the IgE in feline allergic dermatitis is uncertain. Therefore, allergic tests (in vivo or in vitro) are not useful to confirm the diagnosis of atopic dermatitis in cats. Moreover, intradermal testing is of difficult execution and interpretation in cats and serological testing do not differentiate healthy non-allergic cats from those allergic.

It is this context that, once a definitive diagnosis of non-flea non-food hypersensitivity has reached, pharmacological therapy is usually preferred in cats with allergic dermatitis.

Treatment

Allergen specific immunotherapy is scarcely used in cats with non-flea non-food hypersensitivity due to difficult execution and/or interpretation of allergic tests and low evidence of efficacy of immunotherapy (efficacy information based on open studies). However, only clinical response to the specific desensitisation would confirm or rule out the role of allergens detected by allergic testing.

Among pharmacological therapy, oral glucocorticoids are preferred to injectable glucocorticoids. Prednisolone or methylprednisolone are preferred to prednisone, because the latest has a lower biodisponibility due to its low absorption or transformation to the active metabolite in cats. Although cats have been traditionally considered resistant to the glucocorticoids, these drugs also cause serious side effects in feline specie. The most common are cutaneous atrophy, congestive heart disease and diabetes mellitus (in fact, 80% of cats with spontaneous hyperadrenocorticism suffer from diabetes mellitus).

Alternatively to chronic glucocorticotherapy, cyclosporine is a relatively well tolerated and efficient treatment for feline non-flea non-food hypersensitivity. Side effects, mainly gastrointestinal upset and sialorrhea, are observed in some cats during daily treatment. These side effects are reversible and improve spontaneously in most of the cats after reducing administration of cyclosporine. Being a drug that inhibits T cells, its use is not indicated in infected cats FeLV or FIV positive or with a history of malignant neoplastic disease because it could lead to an unfavourable evolution of infectious or neoplastic disease due to reduced immune response. Cyclosporine may affect circulating insulin levels and causes an increase in blood glucose, so the use of cyclosporine in diabetic cats is not recommended. Seronegative cats T. gondii may be at risk of clinical toxoplasmosis if they become infected during treatment. For this reason it should be minimised possible exposure to Toxoplasma in seronegative or possibly seronegative cats (e.g., keep them inside the house and avoid eating raw meat).

References

1.  Favrot C. Feline non-flea induced hypersensitivity dermatitis: clinical features, diagnosis and treatment. J Feline Med Surg. 2013;15(9):778–784.

2.  Belova S, Wilhelm S, Linek M, Beco L, Fontaine J, Bergvall K, Favrot C. Factors affecting allergen-specific IgE serum levels in cats. Can J Vet Res. 2012;76(1):45–51.

3.  King S, Favrot C, Messinger L, Nuttall T, Steffan J, Forster S, Seewald W. A randomized double-blinded placebo-controlled study to evaluate an effective ciclosporin dose for the treatment of feline hypersensitivity dermatitis. Vet Dermatol. 2012;23(5):440–e84.

4.  Roberts ES, Speranza C, Friberg C, Griffin C, Steffan J, Roycroft L, King S. 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 dermatitides. J Feline Med Surg. 2016.

5.  Roberts ES, Tapp T, Trimmer A, Roycroft L, King S. Clinical efficacy and safety following dose tapering of ciclosporin in cats with hypersensitivity dermatitis. J Feline Med Surg. 2015.