The allergic patient can present with myriad symptoms, all related to the underlying cause. As is the case with atopic dermatitis, the symptoms manifested result from an "overproduction" of allergen specific IgE to environmental allergens.
The allergic patient can present with myriad symptoms, all related to the underlying cause. As is the case with atopic dermatitis, the symptoms manifested result from an "overproduction" of allergen specific IgE to environmental allergens. Cutaneous adverse reactions to food (ARF) are a result of either "true" food allergy related to the overproduction of food allergen specific IgE, or a food intolerance which is not a true immunologic reaction. Patients with flea allergic dermatitis produce excess IgE in response to flea saliva and display clinical signs somewhat distinctive to the syndrome. However, overlap can occur between the 3 allergic syndromes and it is not uncommon to encounter a patient that suffers from both atopic dermatitis and adverse reactions to food that also experiences a seasonal flare consistent with exposure to fleas. The symptoms that are typically reported by the owner that are attributed to the previously diagnosed allergic diseases are then that much more intense and often are much more controllable with the institution of appropriate flea control measures. Thus recognizing, addressing and managing the threshold effect of pruritus stimulators is key to success.
The patient with unilateral otitis.
Differential diagnoses for this patient include a foreign body, neoplasia, hypothyroidism and ARF. Once the foreign body or neoplasia can be eliminated, either an elimination diet trial and/or thyroid testing are performed based upon additional clinical signs that may be present. Consider delaying thyroid testing if the patient has received oral or topical corticosteroid therapy for the otitis. Resolution of the secondary yeast and/or bacterial infections must occur in order to interpret the results.
The patient with recurrent otitis.
Differential diagnoses for this patient include allergic disease (atopy or ARF) or endocrinopathies based upon additional clinical signs. Again, the secondary infections must be resolved in order to further identify the underlying cause. Allergic otitis without secondary infections does occur and can be managed by addressing the underlying cause or with mild topical corticosteroids, such as hydrocortisone containing otics.
The patient with intense non-seasonal pruritus.
Differential diagnoses include CARF and scabies infestation. Secondary infections (especially Malassezia spp.) must be treated and resolved prior to considering the pruritus intense and non-seasonal. Look for GI symptoms as well, such as frequent bowel movements (> 2 per day), borborygmus, vomiting, frequent grass-eating behavior, poor appetite, etc. Always eliminate scabies as a differential diagnosis with either an ivermectin or selamectin trial (every 2 weeks for 3 treatments, thus total of 2 life cycles) or use weekly lime sulfur dips to treat the pruritus as well as rule out scabies as a cause for the pruritus (6 weekly dips will satisfy the 2 life cycles requirement).
Novel protein diets are currently the most reliable method (other than home cooking) based on recent data. Some patients will continue to fail hydrolyzed diet trials based on pruritus alone, although the lesions (erythema, lichenification, etc.) may appear improved.
The patient with mild seasonal pedal or facial pruritus.
This patient is the poster child of atopy and can benefit from either seasonal administration of corticosteroids (when used judiciously), management with fatty acids and/or antihistamines, or hyposensitization. The younger more mildly affected patient often benefits from hyposensitization alone rather than the older, more severely affected patient that will typically require therapy in addition to hyposensitization. Most atopics peak in reference to the severity of symptoms by the age of 6 years, however the effects of chronic secondary infections as well as corticosteroid excess can make these symptoms appear to worsen with age.
Crucial to the management of an atopic patient is avoidance as well as management of secondary infections. The main route of exposure is now thought to be via percutaneous exposure rather than inhalation, thus wiping the feet after a trip outside can be very helpful in decreasing exposure. Shampooing not only hydrates the skin and can address any secondary infections present, but it also removes pollens and mold allergens from the hair coat and skin, thus further decreasing exposure. House dust mite impermeable box spring, mattress and pillow covers are also essential in the patient that displays more perennial symptoms.
The patient with perianal pruritus.
Again, consider atopy or ARF based upon clinical presentation. Patients with ARF often present with their main clinical signs focusing on "ears and rears", however some atopics will only display perianal pruritus. Often these patients have previously had anal sacculectomies for chronic anal sac problems but continue to have symptoms associated with this area despite removal of the structures. While some allergic patients definitely tend to require more frequent anal sac expression, this is most likely related to chronic inflammation in the region creating increased sebaceous secretions and thickening of the surrounding tissues that complicates normal anal sac emptying—similar to the changes that occur in allergic patients with allergic otitis.
The patient with recurrent pyoderma.
Based upon the signalment, if this patient continually has non-pruritic pyoderma (almost always non-pruritic due to the "self-medicating" effect as a result of endogenous steroids), screening lab work for hyperadrenocorticism (HAC) should be considered. CBC, Chemistry panel and UA can be very helpful prior to proceeding with an ACTH stimulation test or LDDST. Some patients with HAC will have a hyposthenuria or isosthenuria and a normal Alkaline phosphatase value, however additional clinical signs are often revealed upon further questioning of the owner. In addition, some patients with an ARF will simply have a recurrent pyoderma as their main clinical sign. The patient with ARF will however, be pruritic compared to the non-pruritic pyoderma of a patient with HAC.
The patient with pruritus only associated with lesions.
It is important during the treatment of this patient to determine if the patient is pruritic first, and creating the papules, pustules, crusts, etc. or if the lesions are present first and then the pruritus occurs. If the pruritus is present initially, often a short course of oral corticosteroids (such as a combination antihistamine with prednisolone) is required in order to completely resolve the secondary pyoderma. This is one of the very few situations in which I will reach for steroids when treating a secondary bacterial infection. If the lesions are present first and contributing to the pruritus, then I focus on the bacterial infection first. With the increasing frequency of methicillin-resistant staphylococcal infections, if steroids are used concurrently with antibiotics, choose a bactericidal antibiotic and treat for a longer period of time than the standard 21 days. If new lesions develop, despite administration of an appropriate antibiotic, then proceed with aerobic culture, as it is likely the pathogenic organism is resistant to the administered antibiotic therapy.
The other group of diseases associated with this history is a patient with autoimmune disease. Patients with pemphigus foliaceus (PF) can mimic the patient with antibiotic resistant pyoderma. Not all patients with PF have lesions affecting the pads, planum and pinnae. **This is where cytology findings are extremely helpful**
The older patient with non-seasonal pruritus.
Why is this patient just now demonstrating clinical signs? If the patient attends a boarding or grooming facility this could be "scabies incognito" or potentially a neoplastic condition. If secondary infections are present and resolved yet the unexplained pruritus continues, or the secondary infections do not resolve as expected, consider skin biopsy for histopathology sooner rather than later. Cutaneous (epitheliotropic) lymphoma can mimic allergic or parasitic skin disease.
Diagnostic testing dilemmas:
Serum testing versus intradermal testing for atopic disease.
The main reason for performing serum or intradermal testing for atopic dermatitis is to determine what to put into the hyposensitization vaccine. Neither methodology will prove or disprove if the patient is "allergic". The patient must not only produce excessive allergen specific IgE, but also display symptoms. False positive results can and do occur with both testing modalities, thus every other "itchy" disease should be ruled out prior to performing either test. In some cases the best option for the patient is to perform both types of tests and combine the results.
Beyond the obvious differences in ease of performance and availability, the real question is, what to do with the results??? If the patient displays seasonal symptoms, but the serum test fails to identify significantly positive results to the predominant allergens present during the patient's symptomatic seasons, the validity of the results should be questioned. The same reasoning should apply for the patient with non-seasonal symptoms whose test results reveal only seasonal allergens. There also exists a subset of patients who fail to react to either type of testing and are best treated with medical management.
Hydrolyzed versus novel protein test diets for CARF.
Simply stated, homemade test diets are the best for ruling out ARF. That being said, compliance with the test procedure itself improves with a prepared commercial diet. Since it is hard enough to obtain a truly exclusive 12 weeks test period, it is important to strive for a "yes or no" answer upon completion of the trial. Eliminating variables that can mislead interpretation of the test can be extremely difficult, especially during the holidays. Ensure the owner is not feeding flavored heartworm preventative, not using flavored toothpaste or any flavored medications, such as chewable thyroid supplementation, antibiotic tablets or nonsteroidal anti-inflammatory medications.
The debate continues regarding hydrolyzed and novel protein diets. Common dietary allergens for the dog include: chicken, beef, corn, soy, wheat, eggs and dairy. Most hydrolyzed diets utilize either chicken or soy as the protein source. Evidence exists in the literature to support either type of test diet. However, it is important to remember up to 20% of dogs allergic to a certain protein will fail a hydrolyzed version of that test diet.
When should hyposensitization be recommended ..... is cyclosporine (Atopica®) worth the expense?
For the end-stage allergic patient with chronic severe symptoms, cyclosporine may be a "magic pill". There are multiple uses for this drug and each case should be approached individually. For a young mildly affected patient it would be prudent to offer hyposensitization prior to recommending a potentially lifelong medication. However, for vaccine failures or those with constant and severe problems, cyclosporine may be the answer.