Atopic dermatitis

6 Atopic dermatitis


Atopic dermatitis is a genetically determined pruritic dermatitis, associated with an immediate (type 1) hypersensitivity to specific environmental allergens. It is one of the most common causes of chronically recurring inflammatory skin disease and involves complex interactions of environmental, microbial, genetic, immunological and pharmacological factors.

The most common presenting signs are pruritus, erythema and secondary microbial infections. The distribution of the pruritus and the lesions typically involve the face, the ears, the ventral aspects of the abdomen, the perianal areas and the feet. The lesions vary from erythema and salivary staining, to self-induced alopecia, hyperpigmentation, lichenification, scaling, crusting and erosions. Otitis externa is seen in four out of five cases, usually involving the concave aspects of the pinna and the vertical ear canals. Recurring conjunctivitis, periocular dermatitis and sneezing may be evident in some cases.

Secondary microbial infections with Staphylococcus spp. or Malassezia pachydermatis are frequent findings in cases of atopic dermatitis and their importance should not be underestimated. Commonly, one of the first signs of the onset of atopic dermatitis is the development of a cutaneous yeast or bacterial infection, and infection is a major reason for the flare-up of pruritus in apparently well-controlled cases and one of the most common reasons for clients seeking veterinary attention. Clinical signs associated with staphylococcal infections include papules, pustules, epidermal collarettes, scaling and crusting. Malassezia dermatitis tends to cause erythema, greasy secretion and the matting of hair shafts over occluded areas such as the ventral neck, or between the digits.

It is common for the pruritus to be present initially only during the summer months, but with the passing of time it tends to become a year-round problem.

At least three of the following major and minor criteria should be satisfied to make a diagnosis of atopic dermatitis:

Major criteria

Minor criteria


A full physical examination should be carried out prior to examining the skin. The dermatological examination should include all of the skin, extending from the tip of the nose to the tip of the tail and from the dorsum to the pads of the feet. One of the biggest pitfalls is to examine only the affected sites, thus missing other clues that could aid the diagnosis.

The early signs of atopic dermatitis can be subtle and there may be no other clinical signs other than pruritus, although, as in this case, many dogs will have erythema, self-induced alopecia, excoriations, papules, hyperpigmentation and other changes associated with secondary microbial overgrowth or infections. Some individuals will show erythema of the concave aspects of the pinna and the vertical ear canals without any history of ear disease.

The significant clinical findings in this case were:


In all cases, unless there is an immediate diagnosis, it is best to formulate a list of differential diagnoses and methodically rule each one in or out. This list is drawn up from a consideration of the history and clinical signs, the latter comprising both the general pattern of disease as well as individual lesion recognition. This case is typical of many cases of pruritus in that the differential diagnosis list was quite extensive.

In this case the lesions consisted of inflammatory and non-inflammatory alopecia, hypotrichosis, papules, epidermal collarettes, acute moist dermatitis and erythema.

There were also two different types of hair loss. There were areas of self-induced alopecia and inflammation, and other areas of alopecia where the skin was not inflamed. In this case, the non-inflammatory alopecia over the caudal thighs was unlikely to have arisen because of self-trauma or a folliculitis (the common causes of inflammatory alopecia). This presentation of non-inflammatory alopecia is common in Staffordshire bull terriers with pattern alopecia, which is a poorly understood, non-inflammatory alopecia that results in so-called ‘miniaturization’ of hair follicles and in the well-recognized, breed-associated patterns of alopecia.


Staffordshire bull terriers are genetically predisposed to demodicosis; therefore, skin scrapings and hair plucks should always be performed on this breed, or in any case where there is evidence of papules, pustules, alopecia, crusting or scaling. Primary lesions such as papules are commonly associated with staphylococcal infections and/or sarcoptic mange. Cytology and response to therapy are used to confirm the involvement of secondary pyoderma and Malassezia dermatitis, both of which can contribute significantly to the degree of pruritus.

Diagnostic tests: The following diagnostic tests were performed:

Therapeutic trials: Initially, the following therapeutic trials were performed concurrently:

Re-examination: On re-examination 4 weeks later, the pruritus had persisted but the papular lesions had resolved and no microbial organisms were seen on repeat cytology. The ongoing pruritus confirmed an underlying allergic aetiology.

Dietary trials: To rule out the involvement of an adverse food reaction, a hydrolysed diet was fed for 8 weeks. No other foods and only water to drink were allowed during this period. Weekly bathing with an antimicrobial shampoo was continued. Flea control was continued using imidacloprid every 4 weeks. The pruritus persisted during this period, with intermittent episodes of increased pruritus. In this case the diet trial ruled out an adverse food reaction as a cause of the disease.

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Atopic dermatitis

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