Help for the uncontrollably itchy (Proceedings)
Apr 01, 2009
CVC IN WASHINGTON, D.C. PROCEEDINGS
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 RevolutionÂ® 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. One group of commonly forgotten allergens is environmental allergens. Be sure that nothing at home has changed that corresponds to the increase in pruritus. Also, if the patient is sensitive to mold or house dust mite, environmental control of these allergens is as important as desensitization. Contact allergy can start at any age, even as young as 3 to 4 months. Pruritus can be mild to severe, and seasonal or non-seasonal. The lesions of contact allergy typically affect hairless or sparsely haired areas. There is usually a primary papular eruption, but more chronic cases may show only secondary alopecia, lichenification and excoriations. There may be a history of a rash that develops within hours, and then disappears just as quickly. The onset may be acute or gradual and there is usually a worsening over time. High doses of steroids may be required to control symptoms. Making a diagnosis of contact allergy can be extremely challenging. It takes a great deal of detective work on the part of the owner and the clinician. Detailed information about the home environment is needed. This should include types of flooring in the house, types of flooring outside the house, cleaning products used, as well as plants, mulches, etc. that are contacted outside. Diagnosis is made by avoiding the allergen. The patient can either be removed from the environment for at least 10 to 14 days, or the patient can wear clothes to cover the affected areas. If the lesions clear or greatly improve with either of these measures, then contact allergy is very likely. The best treatment for contact allergy is avoidance of the offending agent. Flea allergy is another common cause of uncontrollable pruritus. It is important to be sure the clients are doing good flea control and that the patient does not have clinical signs compatible with flea allergy. To ensure good flea control, clients need a good idea of what to expect from the flea product they are using and how to use it properly, and they need to understand both the flea life cycle and how to do environment flea control. Other biting insects can cause symptoms similar to flea allergy dermatitis. These include mosquitoes and Culicoides. In our specialty practice in Florida this is a fairly common hypersensitivity. Unfortunately, most private practitioners do not know about these allergies and therefore they go undiagnosed and untreated. The history usually includes proximity to water, access to the outside and possible owner complaints about biting insects. As mentioned above, hypersensitivity to these insects can look similar to flea allergy dermatitis. They can also cause generalized pruritus and granulomatous lesions. Diagnosis is made by intradermal testing with mosquito and Culicoides antigen. If this is not available, diagnosis can be made by resolution of signs with the use of insect repellents. At this time permethrins are the best therapy. Dogs must be treated daily with low concentration sprays or gels (<1% permethrins) or one to two times weekly for high concentration sprays (2%). The high concentration spot-on products that are available will not control insect hypersensitivity unless they are used every one to two weeks (off label use for most products). Other ways to help control mosquito/Culicoides hypersensitivity are to keep pets in at dawn and dusk when the insects are most active and use environmental insect control. Problems occur when the patient or client is sensitive to permethrins. Skin so soft or natural repellents can be tried in these instances. Hyposensitization is still the best long term treatment for atopic dermatitis. It is important to tell your clients that initial response to hyposensitization usually takes a minimum of 4 to 6 months. It can take 12 to 18 months to see a patient's full response. If a dog is not responding the way you expect, then you may want to vary the dose and interval of injections to maximize its effect. Also if there are more that 15 to 20 allergens you may want to have more than one vaccine. Most patients with uncontrollable pruritus are going to need drug therapy of some type. Glucocorticoids are still the best anti-inflammatory and should be given orally so they can be titrated to the lowest dose. Start with prednisone at a dose of 0.5 to 1.0 mg/lb daily. This dose should be slowly tapered over weeks to months, until you get to the lowest every other day to every third day dosing. If the patient cannot take prednisone , you can try methyprednisolone, dexamethasone or triamcinolone. Another option is to try Temaril P. Cyclosporine is also extremely effective in severely pruritic patients. Be sure to use at least 5 mg/kg daily and remember that it may take 4 to 6 weeks to take effect. Other systemic drugs that may help are pentoxifylline and omega-3 fatty acids. Topical therapy can also be helpful in controlling severe pruritus. It helps to decrease pollens that are percutaneously and orally absorbed. Of particular help in areas of focal pruritus are ProtopicÂ®(tacrolimus) and SynoticÂ®(flucinolone in DMSO). To help demonstrate the above principals we will discuss several clinical cases. In conclusion, when dealing with the uncontrollably itchy it is important to remember that one particular therapy is not going to give you 80 to 100% improvement by itself. Continue adding therapies until you get the patient to an acceptable level of pruritus. Do not give up any advantages. If you are not sure a therapy is helping, stop it and watch for worsening of signs.