Managing patients with allergies can sometimes be challenging especially if their condition follows no particular pattern. There can be many reasons for unexpected flare ups. Recognising these and treating accordingly will greatly benefit the overall management of each individual patient.
Malassezia and Staphylococcal infections are recognised as one of the major flare factors contributing to pruritus, especially in atopic dermatitis. Cytology and culture and sensitivity testing are essential tools for identification and instituting appropriate therapy. Pruritus can be variable in Staphylococcal pyoderma, but is normally a common presenting sign in cases with Malassezia dermatitis. In most cases, Malassezia dermatitis and bacterial pyoderma are associated with an underlying hypersensitivity disorder. Successful management requires controlling both the underlying disease and the infection itself. Regular checkups are essential for early recognition of microbial infections and excellent atopy management. Some allergy therapies are immunosuppressive in nature and could predispose to secondary infections. It may be necessary to review the patient’s management plan carefully and make adjustments as appropriate.
A proportion of atopic dogs develop IgE-mediated hypersensitivity reactions to Malassezia and/or Staphylococcus antigens, which could contribute to the inflammation and/or pruritus.
Therefore, it would seem logical to include these allergens in the immunotherapy. Malassezia and Staphylococcus are, however, not commonly included in environmental allergen panels of
serological tests and have to be requested separately.
Ectoparasites should always be on the list as a potential cause for flares. Flea bite hypersensitivity or flea allergic dermatitis is common and should always be suspected as a flare factor in atopic patients, since they are predisposed. Dorsolumbar dermatitis is highly suggestive and a unique feature of flea allergy dermatitis. One third of animals fail to show any evidence of fleas or flea faeces and a positive response to aggressive flea control is needed to confirm the diagnosis. Intensely pruritic patients demonstrating an itch-scratch reflex should alert us of a possible sarcoptic mange infestation. History (signs of contagion/zoonosis, indirect contact with foxes or infected kennels) and clinical features (predilection sites – pinnal tips and margins, elbows, hocks and ventrum) are suggestive of scabies and often allow a tentative diagnosis. Multiple skin scrapings (superficial and deep) are needed to identify mites or eggs, but this is poorly sensitive. In approximately 50% of cases, mites cannot be demonstrated. Sarcoptes-specific IgG ELISA testing has a high sensitivity and specificity and can aid a diagnosis. Another intensely pruritic condition is cheyletiellosis, which predominantly affects the dorsal trunk. Scaling is variable, but can be intense (“walking dandruff”). Superficial skin scrapings or tape strip preparations
are useful methods to identify mites or eggs.
Mites cannot be demonstrated in all animals and trial therapy may be necessary to confirm a diagnosis. Even though harvest mite infestation is a seasonal threat, it may occur all year round
in warmer climates and changing weather patterns. Orange crusts, which are clusters of larvae, are normally found in the interdigital regions, ventral abdomen, in the folds of the base of
the pinnae or medial canthus. Demodicosis should be considered as a potential differential diagnosis in patients receiving long term immunomodulatory drugs, such as glucocorticoids or oclacitinib. West Highland white terriers can present with a pruritic form of demodicosis, which could be confused with atopic dermatitis. Deep skin scrapings are a sensitive technique, as there are usually high numbers of mites, and hair plucks can be useful for sites that are difficult to scrape.
Whenever there is poor response to glucocorticoids, antibiotics or antiparasitic treatment, dermatophytosis should be considered. Young, old and immunocompromised animals appear to be more susceptible. A breed predisposition (e.g. Persian cats or terriers) should also be taken into account. Tooth brush samples, hair plucks/scrapes and scales should be submitted for culture or PCR testing.
In uncontrolled atopic patients, it is also important to review the possibility of a cutaneous adverse food reaction (CAFR). Has an exclusion diet trial been performed in the past and if so, has this been strictly pursued? CAFR can also cause gastro-intestinal (GI) signs, such as softer faeces, flatulence, colitis or an increased number of bowel movements. However, the absence of GI
signs does not rule out CAFR. Engaging the owners by keeping a pruritus and faecal diary and explaining the process properly will result in a valuable diagnostic outcome. It can be difficult
selecting a suitable diet for the dietary trial, especially in patients where the dietary history is unknown. The Cyno-DIAL®/Feli-DIAL® and Avacta’s SENSITEST® have a high negative predictive value, which can be a helpful adjunctive test when deciding on the most suitable diet.
House dust mites are the most important source of allergens for canine atopic dermatitis worldwide. Therefore house dust mite control measures are relevant and can be effective in patients hypersensitive to such allergens. This has to be continued lifelong as part of the patient’s management plan. There are various measures for dust mite control. Due to the long persistence of mite allergen in the environment, a benefit is likely to take some months to occur.
Allergen-specific IgE ELISA or intradermal allergy re-testing may be considered in patients experiencing flare ups, where the pruritus was previously well controlled or where the patient’s environment has changed in order to identify additional allergens contributing to the condition.
Finally, older patients presenting with skin problems, but no history of skin disease, or patients that are completely uncontrolled, should raise suspicion that this may not be an allergy.
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