Help for the uncontrollably itchy (Proceedings)


Help for the uncontrollably itchy (Proceedings)

Apr 01, 2009

What do you do with those dogs that have been diagnosed with atopy but are not getting better or better enough with treatment? Unfortunately, there are no magic potions either from the past or present that are going to easily fix these patients. Owners of these dogs need to understand some basic concepts about pruritic diseases. First, pruritus is a common presenting sign for both allergic and non-allergic dermatopathies. Second, your long term goal is not necessarily to stop the itch completely, but to decrease it to a level comfortable for both the client and the patient. Third, pruritic diseases are not mutually exclusive. This means that the same patient can have 3 or 4 different problems that make him itch.

There are also several basic rules about dermatologic diseases that the clinician must remember. First, secondary infections with both bacteria and yeast are common in allergic patients. Second, there is no standard therapeutic plan that works for all allergic dogs. Therapies are additive and must be tailored to the individual patient and client. And finally, many allergic diseases are lifelong and have recurrent flare ups. Successful management of these patients requires a significant financial and time commitment from the client.

So let's get back to basics. Be sure you are dealing with allergies and not something else. In the uncontrollable itchy the first diagnosis to look for is scabies. These patients may not eat or sleep well because of pruritus and can lose a significant amount of weight. The problem is that diagnosing scabies can be difficult. Only about 50% of dogs with scabies will have positive skin scrapes. Therefore, it is very important to treat for scabies to rule it out. If using Revolution® or ivermectin, be sure to treat every other week for 3 treatments. Remember that for the first one to two weeks the patient may be worse before he gets better.

Secondary infections are extremely common and can make seasonal pruritus become non-seasonal. Bacterial infections are usually caused by staphylococcal organisms, but may also be due to E. coli or Pseudomonas. We are also seeing more cases of methicillin resistant Staphylococcus species. Therefore, if pyoderma lesions are not improving satisfactorily in the first two to three weeks with empirical antibiotic therapy, a culture should be done. The length of therapy for a superficial bacterial infection is minimally three to four weeks. If there is a deep bacterial infection these should always be cultured and may need antibiotics for 6 to 8 months. A good rule of thumb is that the lesions should be completely gone or static for at least 10 to 14 days before stopping antibiotics. Yeast infections can also cause extreme pruritus. Some of these patients are thought be having seizures because of the convulsive movements they make. Most yeast infections respond to three to four weeks of therapy. Unfortunately, allergic patients tend to be more susceptible to these infections so chronic weekly therapy may be recommended.

Dermatophytosis is usually a mildly pruritic disease, but in some cases it can cause fairly intense pruritus. Remember that patients on immunosuppressive therapy, like many of our atopic patients, are more susceptible to dermatophytosis. Patients with chronic pruritic dermatoses that are on immunosuppressive drugs, go to the groomer, or are frequently in contact with other dogs or cats should be fungal cultured.

Demodicosis caused by Demodex canis typically presents with mild to no pruritus. Unfortunately, it can sometimes be very pruritic. Demodicosis is more common in patients on immunosuppressive therapy. Do not forget about demodicosis in those patients with pruritic, lichenified feet. The short demodex mite of dogs usually causes moderate to severe pruritus and can mimic allergic disease. Unlike Demodex canis , many times only one or two mites are found on survey skin scrapes. Demodex injai, a third Demodex species, can also cause increased pruritus. These mites are usually seen associated with steroid use.

There are numerous other diseases such as mycosis fungoides, hepatocutaneous syndrome, and generalized mastocytosis that can cause intense pruritus. If you suspect any of these, a biopsy should be done to obtain the diagnosis.

Once you have ruled out other causes for the remaining pruritus, it is time to rule out other allergic diseases so you are sure your patient is suffering from atopy alone. Food allergy can vary tremendously in its presentation. It can start at any age, from 3 months to as old as 12 years of age. Food allergy usually causes moderate to severe non-seasonal pruritus, but it can sometimes cause little to no pruritus. The onset may be sudden or gradual. Any body part may be involved and response to steroids is variable. Food allergy is best diagnosed with a "hypoallergenic" diet trial. This involves feeding a homemade or commercially prepared diet consisting of a single novel protein and carbohydrate. The patient must not receive any other food for at least 6 to 8 weeks. This includes treats, rawhides, flavored toys, flavored drugs or supplements, and "cheese to get the pills down". Most food allergic dogs start to show improvement within 3 to 4 weeks although it may take 4 months before the patient's improvement is complete. The diagnosis of food allergy is confirmed if clinical signs recur when the old diet is re-introduced. Challenging the patient with individual ingredients for 7 to 14 days can identify the actual offending protein(s). The food trial is the only accurate way to diagnose food hypersensitivity. Serum testing (RAST, ELISA) and intradermal testing for food substances is extremely inaccurate and not recommended.

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