Atopic dermatitis

6 Atopic dermatitis




INITIAL PRESENTATION


Pruritus with erythema, alopecia, papules and epidermal collarettes.



INTRODUCTION


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



• First signs between 1 and 3 years of age (but may range from 6 months to 3 years)

• Pruritus that is generally glucocorticoid responsive

• Typical distribution of pruritus and lesions (facial, pedal, ventral and may involve perianal area)

• Otitis externa or bilateral erythema of the concave aspects of the pinna

• Chronic or chronically relapsing

• Genetically predisposed breed.

Minor criteria



• Bilateral conjunctivitis

• Facial erythema and cheilitis

• Recurrent staphylococcal pyoderma

• Seasonal or non-seasonal intermittent exacerbations

• Positive intradermal allergy test or elevated allergen specific serum IgE levels.



CASE PRESENTING SIGNS


A 23-month-old female Staffordshire bull terrier was presented for pruritus, erythema, papules, epidermal collarettes and alopecia.



CASE HISTORY


The main points of interest in the history were:


• It was acquired 9 months earlier, with mild dermatological signs already present.

• The pruritus had been intermittent; it was worse in the summer but was also present during the winter months.

• The pruritus mainly affected the face, ears, feet and ventrum.

• The owner was also concerned at the hair loss on the caudal thighs.

• There were no other animals in the house, but casual contact with dogs in the parks and with relatives’ pets.

• Flea control had been used when the dog was first acquired, but not since.

• The dog was fed on a commercial proprietary diet, treats and table scraps.

• The pruritus, but not the rash, was glucocorticoid responsive.

• There was no history suggestive of systemic involvement.

In summary, this was a young dog, of a breed predisposed to atopic dermatitis, with a non-seasonal, glucocorticoid-responsive, facial, aural, pedal and ventral pruritus, and flea control was intermittent.



CLINICAL EXAMINATION


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:


• Papular rash on the ventral neck (Fig. 6.1).

• Small patch of acute moist dermatitis on the right side of the face.

• Bilateral periocular dermatitis and alopecia (Fig. 6.2).

• Erythema of the concave aspects of both the pinnae.

• Hypotrichosis and erythema of the flexural aspects of the carpi and the extensor aspects of the elbows (Fig. 6.3).

• Alopecia, papules and epidermal collarettes on the ventral chest and abdomen.

• Non-inflammatory alopecia of the caudal thighs (Fig. 6.4).

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Figure 6.1 Papules, erythema, alopecia and excoriations on the ventral neck.


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Figure 6.2 Periocular erythema and alopecia.


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Figure 6.3 Alopecia and erythema on the flexural aspects of the carpus.


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Figure 6.4 Symmetrical alopecia on the caudal thighs.




DIFFERENTIAL DIAGNOSES


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.



Differentials for the inflammatory alopecia/erythema/papules/epidermal collarettes



• Demodicosis

• Sarcoptic mange

• Secondary microbial infections
• Malassezia dermatitis

• Superficial staphylococcal pyoderma

• Atopic dermatitis

• Flea bite hypersensitivity

• Adverse food reaction

• Dermatophytosis.


Differentials for the non-inflammatory alopecia



• Pattern alopecia

• Demodicosis

• Dermatophytosis.


CASE WORK-UP


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:


• Skin scrapings, hair plucks and coat brushings, which were negative for Demodex canis and Sarcoptes canis mites.

• Hair plucks, which revealed both anagen and telogen hairs.

• Examination of coat brushings, which did not reveal any fleas, flea dirt or other ectoparasites.

• Examination of tape strip preparations from the ventral neck, which showed Malassezia pachydermatis and coccoid bacteria. Both organisms play a secondary role in the pathogenesis of the dermatitis and should therefore be treated.

• Fungal cultures from the hair plucks, which did not grow any dermatophytes.

• Sarcoptes scabiei mites are not always seen on skin scrapings in cases of scabies and likewise a failure to identify fleas or flea faeces on examination does not rule out the involvement of flea allergy dermatitis. Additionally, there was evidence of secondary yeast and bacterial infection that may have been contributing significantly to the level of pruritus. Therefore, despite the fact that this case satisfied sufficient major and minor criteria for the diagnosis of atopic dermatitis, it was important to rule out ectoparasitic disease and resolve the secondary yeast and bacterial infections before proceeding with the investigations into the underlying allergy. Prior treatment of concurrent and secondary diseases allows a baseline level of pruritus to be established before starting a diet trial.

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


• The pyoderma was treated with cefalexin (20 mg/kg b.i.d.) for 3 weeks.

• The Malassezia dermatitis was treated by three times weekly baths with a shampoo containing 2% miconazole/2% chlorhexidine.

• To definitively rule out scabies or flea involvement, selamectin was applied three times at 2-weekly intervals, and the home was treated with a spray containing a combination of permethrin and pyriproxyfen.

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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