Your skin biopsy result is hypersensitivity disorder part 2 (Proceedings)

What We All Know-The History and Physical Examination

The importance of a thorough history is common knowledge. It is difficult to argue the usefulness of pre-printed history questionnaires when the diagnosis is obvious (e.g. fleas in your face) at the time of first presentation. The vast majority of clinicians need little prompting to ask pertinent questions in these cases.

Pre-printed forms completed by the owner are especially useful in many scenarios assuming the client has arrived early enough to complete the form and/or is able and willing to complete the form. Arriving with adequate time to compete the form is greatly over-looked obstacle to their use. Like most people, clients cannot be asked to remember key details without adequate time to ponder the question.  In addition, another point commonly not addressed when advocating the use of these forms is the clients that is flatly unwilling to take the time to complete the form often citing “it's all in the record”.  There are several key things to communicate to the client. First, and most importantly, the information on the form is “their side of the story”. The medical record contains the clinician's side of the story and not everything they said is recorded.  Second, filling out the form completely may save them time and money. It is always better to have more information than not enough. They could provide a golden nugget of information that helps streamline the diagnostic work up and avoid unnecessary testing.  If the situation calls for a completed history form and this is not possible for any reason, the next best step is to use a pre-printed laminated form as a prompt to gather history and then proceed with the visit.

From a practical aspect, skin diseases are rarely life threatening and there is time to send the form home with the client to complete and have them send it back. Secondly, these forms become invaluable assets in multi-doctor clinics where clients see the next available doctor by choice or necessity. Continuity of care is best for pets with chronic problems, but it is not always possible.   Clients become weary and/or can lose confidence in their veterinary clinic if asked repeatedly to repeat the same information over-and-over. Reading a completed history form followed by a review of the visit notes, presents a strong positive image. 

There are many excellent resources that review the steps in a dermatological examination, identification of primary and secondary lesions etc. In this day and age of easy digital imaging, the mantra that a picture is worth a 1000 words was never more-true. Photographs document what the cat looked like at first presentation and over time. This can be very valuable in multi-doctor clinic and especially in chronic skin cases.  In addition, if it becomes necessary to submit skin biopsy specimens copies of the images documenting change over time are of great value to a veterinary dermato-histopathogist attempting to make diagnosis from a six mm biopsy specimen.

 “Flowing the Flow-Chart”

Diagnostic flow charts are most helpful as a visual aid for clients. They allow the client to see the complexity of the diagnosis and the necessary steps needed to make the diagnosis. Obviously, they are also useful in the work up of skin diseases when the diagnosis is not obvious.  However, it cannot be emphasized enough that these are guides, not mandates. Clinical acumen coupled with common sense guide diagnostic and treatment decisions.  Flow charts are available for feline skin diseases based upon the problem (e.g. pruritus, alopecia), body region (e.g. diseases of the face, paws), reaction patterns (e.g. feline symmetrical alopecia), etc. The reason why flow charts “work” is that they present an orderly and rational approach the diagnosis of skin disease working from a point of commonality (most common and/or easy to diagnosis) to less likely. Generically, most flow chart aides for the work up of cats with hypersensitivity reaction use a stepwise approach to work through causes in, more or less, the same order. 

Frustrated Owners and Their Itchy Cats

This discussion refers to cats in which the diagnosis is not obvious, the episodes are recurrent or persistent and/or the duration is long enough or clinical signs severe enough for the owner to become distressed.

Determine the “Urgency” 

From a medical perspective, the history and clinical signs determine the urgency of the disease. From a client's point of view, what defines ‘urgent' varies widely. The decision needs to be a consensus because the urgency of the situation will be the determining factor in selecting diagnostic tests. Obviously, a mismatch between the clinician's opinion and the client's is the first site of problems. Many clients are anxious due to worry that something major has been overlooked and until this concern is addressed via a diagnostic test, the client will be unable to be compliant. On the other hand, frustration may be the source of the urgency.

If the cat is ill, the clinical signs dramatic, and/or the onset acute, an aggressive diagnostic work up needs to be pursued. This becomes especially urgent in older cats with an acute onset of skin lesions. In these cats the work up can include, but not be limited to, skin biopsy of numerous representative sites, medical work up, possible abdominal ultrasound (rule out neoplasia).

Outline the Diagnostic Plan, Write it Down, and Make Copies (And someone photographs the cat!)

Once a cat's skin disease becomes recurrent/persistent or urgent, it is time and cost effective literally to write down the diagnostic plan. This is essentially a “custom” flow chart for the cat. Giving the client a copy ensures they know there is “a plan”. Clients can be encouraged to keep note relative to “the plan”. It makes recheck visits simpler because the “catch up” time is shortened.  The most consistent comments from clients that self refer are “The doctor(s) never remembered what the plan was” or “I never felt like there was any kind of plan”.  If time does not allow for photographing the cat, ask the client to do it and send digital photos to a clinic email address. This works surprising well if the client is able and willing. Below is a copy of an itchy cat flow chart that can be used and copied for clients.

“I spent a lot of money on tests and …..”

Spending money on services and not having “satisfaction” is frustrating. The expectation from most clients is that every diagnostic test is diagnostic when, in fact, this is not the case. For parasitic diseases, a positive test rule in a parasite but a negative test does not necessarily rule it out. Skin biopsy findings are especially important to preface with a clear explanation of what is being asked. In cases where an immune mediated disease or neoplasia is suspected, a likely diagnosis can be expected assuming classic representative samples were obtained. Again another point to make to clients is that the more specimens submitted, the greater the chance one of them will be diagnostic. Sometimes the greater value in a well-selected skin biopsy specimen is finding out what it is not (e.g. neoplasia) rather than what it is (e.g. hypersensitivity reaction). On the other hand, what it is (e.g. hypersensitivity) can be comforting as it indicates that the diagnostic process is heading in the correct direction.

Response to Treatment Trials Diagnostic Approach

In cats where routine diagnostic tests have not yielded any results, another approach to diagnosis might be considered. This would include a series of treatment trials. These treatment trials build upon each other, it is important to “revisit” the problem from the start so treatable, and curable diseases are not missed. The client needs to understand that this “diagnostic test” is a test, otherwise the impression may be “they didn't do any diagnostics... they just kept treating the cat”.

The first steps in a treatment trial diagnostic approach are to rule out ectoparasites and skin infections. There are three treatment trials involved: response to flea control, response to lime sulphur and response to antimicrobial treatment (bacterial and yeast overgrowth). (Dermatophytosis should have been solidly ruled out prior to this decision.)  Of these three treatment trials, the one that will be met with the most resistance by clients is the response to lime sulphur. This is primarily due to the odour of the product. Lime sulphur is used to rule out Demodex gatoi but it is also used to treat for ecto-parasites that may not have been resolved completely by flea control. Mites that roam on the hair coat (e.g. Cheyletiella) or are present in crusted exudate (Otodectes, Notoedres) can be difficult to treat. Alternatively, if the product does have good efficacy against parasites lime sulphur may bring more immediate relief because it is a whole body drenching application. Another complication with lime sulphur is that it can be drying to skin causing some mild pruritus in some cats. Antimicrobial treatment trials, microbial overgrowth in cats is less common than in dogs but is under-diagnosed. In order to prevent misuse of antibiotics and antifungal drugs, and unexpected adverse effects, a high degree of suspicion should be present.

These treatment trials need to be completed before pursing an allergy work up, but the order in which they are performed depends upon the cat's clinical signs. If there is extensive inflammation and exudate reveals inflammatory cells and/or bacteria, antimicrobial therapy may be the best first step. If this is the step, careful examination of the patient should be done to determine if concurrent itraconazole is needed to treat Malassezia. Microbial overgrowth is present because of an underlying trigger that may or may not be present. If the cat is intensely pruritic, the best first choice may be a treatment trial for with lime sulphur. A response to flea control may be indicated.

If response to parasite and microbial overgrowth fail, the next step to consider is a food trial. Food trials in cats are best interpreted in light of no response to parasite treatments and after ruling out combined bacterial and yeast infections.  There is no one “best” diet and the selection of a commercial product for a diet trial or a home cooked diet is a case by case decision. 

• Commercial Diets Vs. Home-Cooked Diets

• How to Conduct a Food Trial

• Troubleshooting the Food Trial

• Managing Pruritus in Cats Undergoing Food Trials

The non-flea, non-parasite, non-other, non-food cat is, by process of elimination, a cat with a hypersensitivity dermatitis.

• Pursing allergy testing and immunotherapy

• Skin biopsy: Pros and Cons

• Response to Medical Treatment

• Long Term Management

References and Recommended Readings

Hnilica KA, Small Animal Dermatology: A color atlas and therapeutic guide Elsevier Saunders, St. Louis 2011

SAMPLE ITCHY CAT CLINICAL FLOW CHART

Owner________________     Patient_________________                   Date________________

Reaction Pattern(s):                 Symmetrical Alopecia             ECG        Miliary Dermatitis   Ulcers/Erosions

Causes of Itching in Cats: The major causes of itching in cats are: parasites, infections, allergies and “rare other causes”. These are listed in order of more common to less common, less expensive to more expensive to diagnosis, and treatable and curable to life-long management. Possible causes are circled. We will revise this list at each follow-up visit.

Parasites: Fleas, Demodex mites, Cheyletiella mites (walking dandruff mites), ear mites, lice other contagious mites, ticks

Infections: bacterial, yeast, dermatophytosis (ringworm)

Allergy: flea allergy, atopy (environmental allergies), food allergy, unknown allergy

Other (rare!): immune mediated diseases, neoplasia

Step 1: The Parasite Hunt

Parasites can be hard to find because cats are fastidious groomers. A positive test rules it in; a negative test does not always rule it out.  It is important to rule out parasites. These are the most common causes of itchy cats, least expensive to treat, and most likely to be cured.

[       ]      Visual exam-parasites large enough to be seen

[       ]      Skin Scrapings-mites

[       ]      Flea Combings-anything large enough to get caught-fleas, ticks, lice, dandruff mites

[       ]      Ear swab in mineral oil- Demodex, ear mites

[       ]      Fecal flotation-mites especially Demodex

[       ]      Response to Flea Control: Rules out fleas/flea allergy,

[       ]      Response to Lime Sulphur: Rules out mite infestations when suspected but can't be found

Note: Parasites are contagious and in contact pets should be treated.

Step 2: Rule Out Infections

Bacterial and yeast infections are overgrowth of normal body flora. If there is a response, the hunt may not be over if there is an underlying ALLERGY triggering the overgrowth.

[       ]      Dermatophyte (ringworm) culture-results take 7-21 days

[       ]    Wood's lamp (screening test for ringworm, negative does not rule it out)

[       ]      Response to combined antibiotics and anti-yeast medications

Step 3: Looking for Allergies

These are response to treatment trials or diagnosis of exclusion. Test results are only meaningful if it is certain causes in Step 1 and Step 2 are not present.

[       ] Rule out flea allergy- Do or repeat a response to flea control! Most common allergy!

[       ] Rule out a food allergy-6 to 12 week strict feeding of a special diet followed by diet challenge

[       ] Environmental allergies- A diagnosis of exclusion