Mejor Aproximacion al Perro con Prurito!

Clinical Manifestation

The lesions observed in diseases associated with pruritus in dogs can be divided into 3 groups:

1.  Self-inflicted injury, secondary to pruritus (i.e., the actions of scratching, licking, biting, pulling hair, and shaking the head). We can observe alopecia, erythema, excoriation, ulceration, crusts, nodules and plaques secondary to licking, and hair color changes (turning red-brown due to the saliva).

2.  The lesions associated with chronic itching, such as lichenification and hyperpigmentation, are linked to prolonged inflammation associated with skin infections that frequently accompany allergic dermatitis and continuous trauma to the skin surface.

3.  Primary lesions, especially papules, which may be a direct result of parasitic disease and/or allergic causes of itching or represent the previous stage of pustules in case of bacterial infection.

In the dog, contrary to what happens in the cat, the type of lesions and their distribution are suggestive of the cause of the pruritic disease. This may be due partly to the fact that the dog manifests itching so less variable than the cat, resulting in fewer clinical polymorphism.

A pruritus mainly distributed on the elbows, hocks and ear margins, associated with erythematous papules and yellow-greyish crusts suggests a scabies. A dorso-lumbar itching suggests a flea bite allergic dermatitis.

In this case pruritus can also be observed in the perineal region, tail and abdomen and be associated with papules. An itch distributed in any, if not all, of the following locations: the face, ears, flexor surface of the joints of the extremities, between toes, axila, abdomen and groin suggests an atopic dermatitis or food allergy.

It is very difficult, if not impossible, to differentiate clinically atopic dermatitis from food allergy, however, the perineal itching is reported as a suggestive clinical sign of the last. Pruriginous otitis externa may be associated with both atopic dermatitis and food allergy.

Diagnostic-Therapeutic Protocol

In the diagnostic-therapeutic protocol the first step is to exclude the causes of itching not strictly allergic, primarily parasitic diseases caused by mites, although considered less likely. Therefore, microscopic examination of skin scrapings, scales and cerumen will be performed in order to identify parasitic mites. However, taking into account that is not always possible to rule out their presence in these diagnostic tests, in the presence of suggestive clinical signs in dogs, it is advisable to perform a therapeutic trial with acaricides.

The next step in the diagnostic-therapeutic protocol would be to eliminate the stimuli, such as fleas, bacteria and/or yeast (Malassezia), which by immunological mechanisms or not, could help to overcome the individual threshold of itching in atopic patients. To exclude the role of fleas, immune mediated or not, in the onset of itching, we should run an anti-parasite treatment for at least 1–2 months. To define the role of bacteria and yeasts it is necessary to perform cytology examination.

The observation of neutrophils and bacteria (pyoderma), or of ≥2 bacteria and ≥5 yeasts for microscopic field immersion (1000 magnifications) makes necessary an antibacterial and/or antifungal treatment.

Once at this point of the diagnostic-therapeutic protocol and if pruritus persists, or if problems caused by bacteria and/or yeasts recur frequently and therefore require continued pharmacological therapy, it becomes necessary to exclude the presence of food allergy and, if necessary, of atopic dermatitis. Both problems could be present simultaneously in the same patient. Diet trial is performed during a period of 4–8 weeks. During this time the subject should be feed only from a homemade diet using a single protein source that has not been previously exposed, or with a commercial hypoallergenic diet. If a reduction or disappearance of the pruritus is observed, to confirm that the result is due to the change of diet, it is essential to perform a provocative test lasting 2–3 weeks with the previous diet. If pruritus reoccurs, it is plausible to diagnose a food allergy. If the provocative test does not get a recurrence of the pruritus, we could exclude a food allergy and, with compatible clinical history and dermatological examination, we were able to diagnose atopic dermatitis.