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
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 Protopic®(tacrolimus) and Synotic®(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.