Diagnosing and treating the pruritic dog (Proceedings)

The objective of my presentation today is teach you how to diagnosis and manage a pruritic dog in a safe and cost effective manner.

When a dog is presented with a chief complaint of pruritus it is essential that you approach the problem in a systematic manner. Not only will this be the most cost effective approach but also it is also less likely that you will misdiagnose the underlying disease.

The simplified approach is as follows

Etiology/Pathophysiology/Diagnosis

Obtaining the signalment is the first step toward diagnosing the pruritic dog. Age, breed and sex can help point you in the right directions. For example, it has been reported that Labrador retrievers have a higher incidence of have a higher incidence of cutaneous adverse food reactions then does the general population. A puppy that is presented for pruritus should have ectoparasites, intestinal parasites and fungal infections on the rule out list. A young adult dog would typically have environmental allergen induced atopic dermatitis and cutaneous adverse food reactions on the high on the differential diagnosis list while a geriatric dog would have ectoparasites, neoplasia (eg cutaneous lymphoma) and infectious diseases secondary to an endocrinopathy as their main differentials.

The next step may be the most important one, obtaining a detailed history! This starts by getting a copy of the dog's medical record. If the dog has had previous skin or ear disease, getting a copy of the medical records may help tremendously in developing a differential diagnosis list. The next step is asking questions that can help narrow the possible causes of the pruritus. Questions that you must ask include:

1. Distribution of pruritus initially and currently.

2. When did these symptoms first occur?

3. Has the EVER had problems with itching or ear infections before? If so, when and how was it treated

4. Where does the dog live- indoor, outdoors, both?

5. Which, if any heartworm and flea preventative is being used and how is it used (yr round or seasonal)

6. Are there any other pets in the household? If so, what kind and are they symptomatic. Are any of the humans in the household showing "new" skin problems? If so, what kind

7. Do they board the dog, take him to obedience school, training or to the groomers?

8. What does the dog eat?

9. How pruritic is the dog today – from 0 (normal dog) to 10 (non stop scratching)? How does that compare to other times?

10. Is today's clinical presentation the best, worse or average since the problem began?

11. How was the progression of the pruritus? Gradual or sudden?

12. Was there a "rash" first or itching first? Or did they occur simultaneously?

13. Do you notice if the symptoms were better, worse or no different or not sure between the different seasons.

After reviewing signalment and thoroughly questioning the owner, the next step is to do a do a complete physical examination.

After the examination you should have a list of differential diagnoses for this pruritic dog. A DIAGNOSIS OF PRURITUS IS LIKE MAKING A DIAGNOSIS OF VOMITING. It is a symptom so you need to follow the word "pruritus" with the phrase "due to". The challenge at this point is to make that a logical "due to" list. Historically information that is of value in making this list is age of onset of the pruritus and the responsiveness of the pruritus to steroids.

Once you have made your differential diagnoses (ddx) you can then do diagnostic testing. I think that by making a ddx list you can make choices in your testing that are most cost effective. Appropriate tests for each disease are listed below.

1. Ectoparasites (fleas, sarcoptes, Cheyletiella, Lice, etc)

a. Superficial skin scrapings, acetate tape impression (unstained); flea combing (helps dx Cheyletiella too), fecal, vacuuming, therapeutic trial w/an ectoparasiticidal agent.

2. Cutaneous adverse food reactions (CAFR)

a. Home prepared elimination diet trial for 60-90 days. Be sure to get a thorough dietary history

b. Commercial novel protein diets or hydrolyzed diets can rule in but NOT rule out CAFR

3. Endocrinopathy- note – these are NOT pruritic without a secondary infection (bacterial or fungal). Dogs that are presented for pruritus and have hypotrichosis/alopecia as a consequence of pruritus rarely would have a concurrent endocrinopathy except for iatrogenic hyperadrenocorticism

a. CBC, serum chemistry profile and urinalysis. Depending on which endocrinopathy you suspect you will do thyroid testing and/or adrenal gland testing

b. NOTE – It is very important to avoid testing thyroid function during and after the administration of some medications because they may alter the thyroid status even after discontinuing them. GC can suppress thyroid function for 30-90 days and potentiated sulfas may suppress the thyroid for up to 30 days after discontinuing the drug

4. Pyoderma

a. Impression smears. Note if there are follicular papules, epidermal collarettes or lichenification you should assume that there is a bacterial component to the skin disease even if organisms are not found. This absence of surface bacteria doesn't rule out a bacterial folliculitis because you can have follicular bacterial infections without concurrent surface infection. Be aware that this is only a general rule since pemphigus foliaceus; dermatophytosis and Malassezia will cause some of these same lesions.

5. Malassezia

a. Impression smears. Finding a cluster of Malassezia is abnormal and should be treated. If you find 1 organism every 1-3 fields (100X) then you should treat it. In contrast to pyodermas I have never seen follicular Malassezia infection without concurrent surface infection.

6. Dermatophytosis

a. Woods lamp and fungal culture

i. Speciate the dermatophyte so that you know the source of the infection

7. Neoplasia (cutaneous lymphoma, mast cell tumor)

a. Impression smears and fine needle aspirates as initial screening tests. Histopath evaluation for definitive diagnosis

8. Contact dermatitis (allergic or irritant)

a. Response to avoidance/discontinuation of medication

9. Nutritional (eg Zinc responsive)

a. Response to supplementation

10. Autoimmune (eg pemphigus foliaceus)

a. Impression smears of a pustule as a screening test. Histopath evaluation for definitive diagnosis.

11. Atopy (environmental allergen induced atopic dermatitis)

a. DIAGNOSIS BY EXCLUSION. In vitro serum testing and intradermal testing DON'T diagnosis atopy, they help select antigen for allergen specific immunotherapy. These tests should be performed once a diagnosis of atopy has been made and allergen specific immunotherapy is planned.

Treatment

There are a variety of therapies for the symptomatic relief of pruritus, but before you do that you should think about addressing the underlying causes. You will be more effective in treating the pruritic patient if you find the "due to" rather than just treat the symptom (pruritus). If the diagnosis has not been established at this point, it is best to treat what you KNOW you have and then see how much pruritus is left over. Unless an obvious cause for the pruritus is found during the examination or initial testing, the next step is, if there is significant pyoderma or Malassezia dermatitis present, treat these secondary infections for 21 days and then reassess pruritus. DON'T use GC during this time since it would make interpretation of response to therapy impossible (was it the steroid or the antibiotic/antifungal therapy that resolved the pruritus?).

1. Antibiotics- A course of antibiotics should be used and CONTINUED for 10-14 days past YOUR clinical assessment that the pyoderma is gone. A three-week course of an appropriate skin antibiotic is the minimum.

a. Appropriate antibiotics include: Cephalexin (10-15 mg/# bid-tid), Clindamycin (2.5 – 5 mg/# bid), Amoxicillin/Clavulanate (10 mg# bid-tid), trimethoprim/sulfonamide (10-15 mg/# bid), cefpodoxime proxetil 5-10 mg/kg sid

2. Antimicrobial shampoo is helpful in treating cutaneous infections (benzyl peroxide or chlorhexidene shampoo).

3. Antifungal therapy- for Malassezia dermatitis - Ketoconazole 3-10 mg/kg sid (with food) for 21 days, itraconazole 5 mg/kg 2 consecutive days/week for 21 days plus an antifungal shampoo (3 or 4% chlorhexidene, chlorhexidene plus miconazole, chlorhexidene w/ketaconazole) and lotion (miconazole)

If the pruritus has resolved when you have only treated the secondary infections it means that the secondary pyoderma or Malassezia dermatitis was the major cause of the pruritus at this time (is only symptomatic when the secondary infection is present – "threshold theory") and it was secondary to one of the following:

1. Seasonal atopy and the season has changed

2. Nonseasonal atopy that is not symptomatic when infection is absent

3. Cutaneous food reaction- that is not symptomatic when infection is absent

4. An endocrinopathy

If a diagnosis has not been established through physical examination and laboratory testing and there is not a secondary infection, the next step is a therapeutic ectoparasiticidal treatment and/or a food trial. A short course of GC in the beginning of the therapeutic trial may be done as long as you know that the dog doesn't have demodex or dermatophytosis. At the end of your therapeutic trial, if the pruritus has resolved w/o the concurrent administration of GC, you have identified your primary cause and can treat accordingly. If the dog has residual pruritus then you have established a diagnosis of environmental allergen induced atopic dermatitis (atopy). Treatment options include:

1. Topical therapy and allergen specific immunotherapy is beyond the scope of this presentation. However in a recent randomized blinded study dogs were either bathed in a whirlpool, bathed w/o a whirlpool and the control group was just wetted dog. Topical therapy and allergen specific immunotherapy is beyond the scope of this presentation. However in a recent randomized blinded study dogs were either bathed in a whirlpool, bathed w/o a whirlpool and the control group was just wetted dog. Pruritus scores improved more than 50% during the first 24 hours after shampoo therapy in the whirlpool in 38.7% of the dogs. Improvement by more than 90% was seen in 16.1% of the whirlpool treatment cases. Conventional shampoo therapy led to an improvement of more than 50% after the first 24 hours in 25%, and of more than 90% in 6.3% of dogs. Only 22% of water treatments in the whirlpool (control group) led to more than 50% improvement during the first 24 hour after therapy, and an improvement of more than 90% was not observed in this group.

2. Glucocorticoids are one of the most effective treatments for non-complicated atopy, and are also the class of drugs with the most serious side effects and potential for misuse.

a. If the dog is pruritic primarily in the areas of pyoderma or Malassezia infection, you should treat the infection BEFORE adding steroids. Many times, steroids won't be needed or a lower dose may be used.

3. Immunophilin-binding molecule (cyclosporine (CSA))

b. These drugs work primarily by inhibiting the activation of inflammatory cells

c. Dosage is 5 mg/kg sid. There may be a 4-6 week delay before seeing full effectiveness so you can give GC during the first 3 weeks to help keep the dog comfortable during this lag time

d. Side effects in dogs are very limited and are primarily GI. Other side effects reported include cutaneous papillomatosis and hyperplastic gingivitis. In order to minimize the most limiting factor of CSA (vomiting) I use Cerenia® for the first 4 days and administer Atopica® with a meal.

e. I use this drug in dogs with AD (note that AD has already been diagnosed) when they are moderately to severely pruritic and:

• The dog has been on chronic GC at the time I see the dog or;

• The owners doesn't want to use GC or;

• When the dog has failed an antihistamine and EFA trial and either "i" or "ii" above or;

• While awaiting response to allergen specific immunotherapy and any of the above situations

4. Antihistamines –antihistamines may be effective in some cases of mild pruritus.

5. Essential fatty acids -may be effective in cases w/mild pruritus especially if combined w/an antihistamine

My approach to a pruritic dog that is a proven atopic. If on presentation there is a pyoderma or Malassezia infection, I will treat those infections w/o using GC. I will recheck the dog in 14-21 days and if the pruritus and pyoderma (or Malassezia) has resolved CONTINUE the antimicrobial treatment for an additional 10-14 days (total of 21-30 days of treatment). If the pruritus continues after the treatment of the secondary infections (or there was not an infection on the initial presentation) then if the pruritus is

1. Mild – antihistamine trial and EFA trial

2. Moderate- I will discuss w/the owner whether the dog needs instant, predictable relief or not. If it does, then I will use a 21 day tapering dose of steroids and EFA. If the dog can tolerate the pruritus for now, then do an antihistamine and EFA trial. If the dog can't tolerate the pruritus then use a tapering dose of prednisone over a 21 day period. The dose of prednisone is 0.25 mg/#/day for 7 days then 0.125 mg/#/day for 7 days and then 0.125 mg/# q 48 hours for 7 days

3. Moderately severe to severe- I will use EFA and a tapering dose of prednisone over a 21 day period as previously described.

a. If the symptoms are for less than 2 months I will treat w/any combination of prednisone q 48 hrs (as long as less than 0.25 mg/#), AH and EFA that controls the symptoms.

b. If the symptoms are more than 2 months/year or the dog needs >0.25 mg/# of prednisone I will

• Use prednisone for short term relief

• Atopica for intermediate term relief

• ASIT for long term relief\

Recommendations for diagnosing and treating the pruritic dog:

1. Be sure to approach the pruritic dog in a systematic, logical approach. By doing so it is less likely to misdiagnosis and mismanage these dogs.

2. Be sure to get a thorough in-depth history, do a complete dermatologic examination, establish a ddx list, select appropriate tests and therapeutic trials. Don't do shotgun therapy. Don't do therapeutic trials that don't help establish a diagnosis.

3. Make a diagnosis and treat a specific disease. Treat the cause not the itch!

4. Try (and almost always) treat secondary infections before administering GC

5. Remember managing the pruritic dog takes time, frequent rechecks and adjustments in therapy. If you are unable or unwilling to commit to these requirements, it would be better to refer the patient.