The District of Columbia Academy of Veterinary Medicine

June 2006

Feline Dermatology

Robert A. Kennis, DVM, MS, DACVD
Texas A&M University

Feline Alopecia

Feline alopecia is a common dermatologic presentation because of the overt clinical findings observed by the owner. Alopecia can broadly be categorized into traumatic induced, hair follicle/shaft damage, and hair cycle abnormalities. As with other dermatologic disorders, an organized history is essential to limit potential differential diagnoses. Simple diagnostic procedures can then be performed to achieve an accurate diagnosis and treatment plan.

Alopecia can be defined as "hair loss". For the purposes of this presentation, alopecia will include all causes of hair loss including an observed thinning of the hair (hypotrichosis) due to broken or plucked hairs. Various stages of shedding can also be perceived as an alopecic disorder.

There are several diagnostic techniques available to aid in a diagnosis. A magnifying lens is helpful to assess the intensity of the alopecia. Hairs from the affected areas should be carefully plucked with a forceps and placed on a drop of mineral on a clean glass slide. A cover slip is applied before examination under low power. This procedure is referred to as a "trichogram". Normal tips of the hairs will come to a tapering point. Broken hairs will have a blunt, fractured appearance and are suggestive of excessive grooming behavior. Occasionally, fungal infected hairs will be identified as "fuzzy hairs" with a distorted cuticle. Fungal spores can also be identified with this simple procedure.

Skin scrapings are an under utilized diagnostic tool in feline dermatology. Demodex mites are an important cause of alopecia. Other parasitic causes of alopecia include chiggers, lice, Notoedres cati, and Lynxacara radovski (cat fur mite). Diagnosis is usually straightforward by use of tape preparations, magnifying lens examination, and skin scrapings.

At times it can be difficult to discern physiologic alopecia from plucked or groomed hairs. In this instance, biopsy and histopathology can be helpful. It is essential to provide a thorough history and description of physical findings to the pathologist. Select lesional skin, and normal haired skin, and make certain that they are identified correctly. Histopathology can be helpful in differentiating congenital/hereditary, endocrine, and telogen defluxion from allergic causes. However, in mildly inflamed, traumatic induced alopecic skin, the results may appear as "normal".

A complete blood count with serum chemistry profile is sometimes useful as a diagnostic tool for feline alopecia. Most allergic causes will have changes in eosinophillic counts but are not diagnostic alone. If there is any clinical evidence of systemic illness associated with the alopecia, then laboratory blood work is indicated.

There are three major causes of feline alopecia associated with damage to the hair follicle or hair shaft. These are demodicosis, dermatophytosis, and occasionally bacterial folliculitis. Other infectious diseases are occasionally encountered.

Demodex cati is a follicular dwelling mite and has a long slender tail, similar to canine demodex mites. Deep skin scrapings are the diagnostic procedure of choice. These mites are usually seen affecting a single pet in the household. Immuno-compromising diseases such as hyperthyroidism, FIV, FeLV, and underlying malignancy should be sought as the cause of demodicosis. Treatment for the cause of demodex is more important than resolving the mites. Although ivermectin and amitraz may be helpful, their side effects and toxicity preclude usage.

Dermatophytosis frequently presents as an alopecic disorder, with or without concurrent scaling. Pruritus may be present. The important historical findings would include the potential for exposure, younger aged patients, and potential involvement of other household animals and people. Diagnosis is made on the basis of examination of plucked hairs and a positive fungal culture. A Wood's lamp examination may be a useful screening tool to provide a tentative diagnosis. However, many false negative results occur. A fungal culture must be done for an accurate diagnosis and identification of the correct genus and species. Treatment options include topical and / or systemic administration of antifungal medications. The selection of an appropriate treatment relies on the age of the animal, intensity of the infection, financial constraints, owner compliance, and herd health status.

Bacterial folliculitis is an uncommon cause of feline alopecia. When severe traumatic alopecia is encountered, a concurrent bacterial overgrowth may ensue. Cytological examination and bacterial culture make a diagnosis. A positive response to antibacterial therapy can be a helpful diagnostic tool.

The most common cause of feline alopecia is due to (pruritic) traumatic causes. These include barbering of the hairs leading to broken hairs, and plucking of the hairs leading to various stages of broken or completely alopecic regions. Traumatic causes are usually pruritic. Occasionally, there is a behavioral cause for excessive grooming but this is a diagnosis by exclusion. Behavioral causes are far less common than pruritic causes.

Feline allergy to fleas, inhaled allergens, and food allergens are among the most common causes of alopecia. A thorough history can help to differentiate pruritic (traumatic induced) from spontaneous alopecia. However, some cats are secretive groomers and the owner many not see the cat lick or pluck at the hairs. Many times there is a concurrent observation of increased hairballs because of the consumption of hair. A fecal exam can also afford a rough estimate of the increased consumption of hair. Fleas might actually be found on the fecal floatation confirming the presence of fleas in the environment. Intradermal allergen testing and or a restricted food trial make a diagnosis.

Behavioral causes of alopecia are usually diagnosed by accurately ruling-out other more common causes. There are times when a striking historical finding at or near the time of the onset of clinical findings is too blatant to ignore. Examples of this might include the addition (or deletion) of a family member or pet, or changes in the environment (construction, outdoor cats forced to remain indoors, etc). The best way to treat behavior induced alopecia is to correct the inciting cause. Corticosteroid usage should be avoided, as there will be no physiologic advantage to using these drugs. By the same token, hormonal drugs should be reserved as a last resort treatment due to their potential for severe adverse side effects. Occasionally, diazepam and newer psychoactive agents can be considered.

When there is a sudden onset of alopecia and other causes of alopecia are ruled out, there are some uncommon circumstances to consider. Cats with urinary tract cystitis may suddenly lick exuberantly at the caudal abdominal region. Similar findings may also be seen in cats with impacted anal sacs. For both of these entities, the traumatic alopecia may extend to the caudal rear limbs, perianal region, and proximal aspect of the tail head. A urinalysis and palpation of the anal sacs are warranted for all middle-aged to senior feline patients with acute onset of traumatic induced alopecia.

There are several causes of alopecia related to hair cycle abnormalities. Congenital hypotrichosis and alopecia universalis (Sphinx cat) is usually a simple diagnosis to make and can be confirmed with histopathology. Endocrine and metabolic causes of alopecia can be a little more challenging to make an accurate diagnosis. Hyperthyroidism can be a cause of alopecia and the straightforward nature of the diagnosis makes it unworthy of coverage at this time. Feline hyper-adrenocorticism is an uncommon disorder that is very difficult to definitively diagnose. Clinical findings include PU/PD associated with mild diabetes and a poor unkempt hair coat. There is usually a thinning of the skin associated with the catabolic effects of excessive endogenous corticosteroid. Diagnosis is made on historical and clinical findings and an abnormal high dosage dexamethasone suppression test (0.1 mg/kg). Treatment with metyrapone can be attempted but there is inconsistent clinical response. Surgical ablation of the adrenal glands would be curative; however, wound dehiscence and poor healing are severe complications. Diabetes mellitus alone or with hyperadrenocorticism should be treated appropriately. Telogen defluxion (or anagen defluxion) can be associated with postpartum alopecia. No treatment is necessary, as the condition will resolve with adequate time allowance. Similar acute onset hair loss may be seen days, weeks, or months following a febrile episode or systemic illness. Accurate historical information and histopathology can lead to a diagnosis.

Immune Mediated And Hypersensitivity Skin Diseases Of Cats

Literally all skin diseases of cats are immune mediated. The focus of this topic will center around those skin diseases which are autoimmune and those which reflect an exaggeration or inappropriate immune response. Individual diseases will be covered with case-based material. There will be a broad review of immune suppressing drugs and their potential side effects.

Pemphigus foliaceus (PF) is one of the most common autoimmune diseases of cats but is still considered uncommon within the general population. There are no known predispositions such as breed or sex. In general, PF is likely to affect middle aged cats but has occurred in older cats (greater than 9 years). This is an important differentiation from canine PF where it is a disease of young to middle aged dogs.

Clinical findings include crusting and ulcerative skin lesions. The typical pustules frequently seen in canine PF are rarely identified in cats. The crusted lesions tend to be locally severe on the ears and face region but may be seen anywhere on the body. The crusted lesions on the head and ears may appear clinically similar to a cat with feline scabies (Notoedres cati). The major difference is that feline PF is usually not pruritic while feline scabies tends to be severely pruritic. Feline atopy, food allergy, and ear mites (Otodectes cynotis) are important differentials if pruritus is present. Feline PF may affect only the claw and nailbeds. The typical history is paronychia affecting more than one digit (the author has seen 1 case of feline PF where only one digit was affected). Frequently these lesions develop a secondary bacterial infection (commonly Staphyloccus sp) and may respond incompletely to antibacterial therapy. A history of relapse after therapy or multiple digit involvement is highly suspicious of feline PF. Additional differential diagnoses when only the digits are involved include: trauma or foreign body, fungal infections of all types including dermatophytosis, primary bacterial infections, pemphigus vulgaris (very rare), contact hypersensitivity, and lupus (very rare).

A tentative diagnosis may be made using evaluation of direct impression skin samples. Acantholytic cells (cells from the spinous cell layer which have lost their desmosomal attachments) are present in all cases of feline PF, but in smaller numbers than canine PF. The important thing to remember is that a severe bacterial skin infection can cause acantholysis. If bacteria are present on cytologic evaluation, appropriate antibacterial therapy should be instituted prior to biopsy collection. This is important because it may be impossible for the histopathologist to make a definitive diagnosis of PF if bacteria are present. A diagnosis of PF should be determined by histopathology evaluation prior to instituting immune suppressive therapy.

The collection of appropriate tissue samples will usually require general anesthesia. A complete CBC, Serum chemistry profile, urinalysis, and FIV/FeLV should be performed. This will function as baseline information prior to immune suppressive therapy and may help to uncover an underlying problem that may be contributing to the lesions. As an example, FIV or FeLV may allow opportunistic infections leading to similar clinical findings of PF. It is recommended that a thyroid evaluation should also be performed for all cats that present with clinical symptoms greater than 8 years. Biopsy techniques are variable depending upon the tissue to be samples. If only the ears are involved, a cosmetic ear trim may be best. Usually the face is also involved so a 6 mm. punch sample will be appropriate. Collecting biopsy tissue samples from the tissue around the nails can be difficult. 3 mm. punch samples can be collected from the skin around the nails but the small sampling size may make a definitive diagnosis difficult. In many cases it might be best to disarticulate an entire claw for histopathologic evaluation. It is very important to provide historical and clinical signs to the pathologist so that they can help to make an accurate diagnosis. In general, feline PF lesions tend to contain very few acantholytic cells making the diagnosis more difficult for the pathologist, especially if bacteria are present.

The treatment options include corticosteroids and other immune suppressive agents. Corticosteroids are always indicated to induce a remission. Depending upon the response to therapy, additional immune suppressive agents may be added. Many cases of feline PF may be managed with only corticosteroids. A poor response to therapy would be suggestive of an incorrect diagnosis or secondary infection. The preferred corticosteroid for induction is methylprednisolone (Medrol Ž) given orally at 2.2-4.4 mg/kg bid (approximately 8 mg bid for a 10# cat is preferred by the author). Prednisolone (but not prednisone) can be used at the same dosages above. Although the higher end of the dosing range is listed in textbooks, it is rarely indicated for therapy. Injectable forms of methylprednisolone acetate (Depo MedrolŽ) should be avoided in most circumstances. For those cats that cannot be pilled, an oral suspension should be formulated before succumbing to injectable therapy. Some cats may develop diabetes so periodic monitoring of blood glucose is indicated. It is highly recommended that a urinalysis with bacterial culture should be performed at least twice yearly. Once a remission is reached, the dosage should slowly be decreased. The ultimate goal should be maintenance with anti-inflammatory dosages on an alternate day dosage. Remission will not be reached is conservative dosages are selected. Also, not all cats can be maintained on anti-inflammatory dosages without a relapse occurring.

Chlorambucil (Leukeran Ž) at 0.1-0.2 mg/kg once daily may be used as adjunctive therapy. Once a remission has been achieved, this dosage may be decreased to every other day. Myelosuppression may occur so periodic evaluation of a CBC is indicated. This drug has a slow onset of activity. Chlorambucil is indicated if there are severe side effects associated with the selected corticosteroid, if it is difficult to achieve a clinical remission at full corticosteroid doses, or if it is not possible to reduce the immune suppressive dosage of corticosteroid without a relapse. Most feline PF cases can be managed without chlorambucil.

Gold salt therapy with aurothioglucose (Solganal Ž) at 0.5-1 mg/cat I.M. once weekly may be considered a last effort therapy. It is never given as a sole therapy but in conjunction with other immune suppressive agents. The mechansism of action is unknown but may relate to immune suppressive effects on lymphocytes and anti-inflammatory effects. Potential side effects include nephrotoxicity, adverse drug eruptions, and blood dyscrasias. This therapy was once considered a primary treatment for feline PF but has lost favor due to lack of clinical efficacy potentially life-threatening side effects. Also, this product has become difficult to obtain commercially.

Cyclosporine (Neoral Ž, Atopica Ž) 3-5 mg/kg/day PO has been used as an immune suppressive agent in dogs and cats. The mechanism of action suppresses induction of T-cell lymphocytes. Side effects may include vomiting, diarrhea, or anorexia. Myeleosuppression is not common. Although this potent immune suppressive agent is effective for some autoimmune diseases, it has been shown to be ineffective for the treatment of feline PF.

Other immune suppressive agents including cyclophosphamide, dapsone, tetracycline/niacinamide, and aziathioprine have been used in the cat with poor results. Newer immune suppressive agents such as mycophenolate may show future promise in treating feline PF.

There are many cases where an inflammatory skin disease, infectious skin disease or adverse drug reaction may mimic an autoimmune disease. Correct biopsy technique is the most important step toward an accurate diagnosis. Avoid the use of corticosteroids until diagnostic samples are collected. A partial to complete response may mask the true diagnosis. If a drug eruption is suspected, use supportive care only. Any drug including corticosteroids can propagate an adverse drug reaction. Use topical patches for pain relief to avoid parenteral medications. A biopsy sample can help confirm the diagnosis of a drug eruption but may not clearly point to the cause. A thorough history may help.

Bacterial Dermatitis In The Cat

Feline bacterial skin diseases present with a variety of clinical presentations. Draining lesions, crusting dermatitis, and papular eruptions are but a few of them. Because these clinical entities over lap with parasitic, metabolic, nutritional, allergic, fungal, and autoimmune diseases, achieving a diagnosis can be difficult. In many cases, the bacterial skin disease may manifest itself as a secondary complication due to trauma or immune compromise. A thorough history followed by a rational diagnostic plan will help to sort through the many variables to arrive at a definitive diagnosis. The purpose of this presentation is to review historical clues and diagnostic techniques appropriate to define the bacterial etiology. Individual organisms responsible for inducing feline bacterial dermatitis will be reviewed including the etiology, differential diagnoses, and current treatment options.

A thorough history is an essential starting point in any medical situation. Signalment and sex status should not be overlooked. Male (intact) cats have a propensity for hunting and fighting and are at a greater risk for certain bacterial diseases. Age can sometimes be helpful in limiting (or expanding) the list of differential diagnoses. The herd health status including the other pets (or people) in the environment may be suggestive of a contagious etiology. The presence of fleas or historical exposure to fleas can be a complicating or primary factor in the dissemination of certain infections (e.g. Plague). It is also important to consider the nutritional status of your patients as diet can be a predisposing factor. If the patient is not a regular at your clinic, FeLV/FIV status, vaccination history, and antiparasitic history should be evaluated. Much of this information can quickly be evaluated with a well prepared questionnaire.

The initial description of the lesion or possibly insighting trauma as observed by the owner will provide useful information. Although the owner may lack the medical terminology we are used to, they can often relay a fairly accurate account of the progression of the clinical findings. If draining lesions are present, the owner should be asked to describe the initial character of the discharge with respect to color, odor, and presence or absence of tissue grains. In many of these cases, the disease is prolonged and the current clinical findings may be very different than the initial presentation. I believe that the owner should be asked what they think the cause of the problem is. More times than not their perceptions are valid. At other times they are amusing and provide a source of humor in lecture situations.

Some of these bacterial diseases are very difficult to diagnose. As such, there may be a significant history with respect to previous diagnostic procedures and treatment outcomes. The client can provide useful experiences relating which medications worked better than others. It is also important to consider dosages, duration of therapy, and owner compliance. Antibiotic resistance due to inappropriate antibiotic selection is a fact of life. When it is apparent that a definitive diagnosis was not made by previous colleagues, it is essential to look for potential causes of failure. Clients quickly lose faith in a clinician who seems to be repeating procedures that did not yield a diagnosis previously. For this reason it is essential to understand the biology of the pathogens on the list of differential diagnoses to correctly select the appropriate culture techniques and come up with an answer.

Examination gloves should be worn whenever the chief complaint entails feline skin disease. Feline dermatophyte and intermediate fungal infections (e.g. Sporotrichosis) can be highly zoonotic. Depending on the bacterial etiology, the zoonotic risk is variable. Even though an organism such as Nocardia sp. is ubiquitous in the environment, the potential amount of organisms within the exudate can be overwhelming, putting ourselves at risk. Clients do not seem to mind that you are wearing gloves. In fact it should be viewed as a positive aspect because you are not transferring other diseases to their pet.

During the physical examination, careful attention should be paid to the hair coat. A small foci of alopecia may indicate the entry of a foreign body or potential site of abscess rupture. Gentle palpation of the skin may reveal fluctuant pockets that may be potential sampling sites for biopsy or culture. Resist the temptation to rupture these pockets until the appropriate sampling equipment is available. When exudation is present, take a moment to document the color, odor, and character of the material. The presence of tissue granules is helpful in limiting the list of differential diagnoses. It is also important to palpate the lymph nodes adjacent to the skin lesions to assess dissemination.

Depending on the clinical and historical findings, a minimum amount of diagnostic procedures are almost always necessary. FeLV/FIV status is essential information. Direct impression skin samples or aspirate cytology assessment is very valuable. The cytologic findings can help limit the list of differential diagnoses and provide a tentative diagnosis while cultures or biopsy samples are pending. In most instances a modified Wright's stain (e.g. Diff-Quik7) will suffice. The identification of the morphologic shape of the bacteria, the types of inflammatory cells present and the identification of intracellular pathogens can be assessed. In highly cellular exudate the use of a Gram's stain will help to identify organisms and will provide additional diagnostic information. Occasionally, the use of an acid fast stain is helpful, but the infrequency of its use does not justify the in house expense. This can be performed by your microbiology lab at the time of sample inoculation. It is important to perform cytology on any sample submitted for culture.

Biopsy and histopathology may provide a definitive diagnosis or help to limit the list of differential diagnoses. Many times the results will suggest additional diagnostic procedures to greater define the disease etiology. Veterinarians can become frustrated with their pathologist because the exact cause of the disease may not be defined. By providing a good history and by selecting representative sites of the disease process you can get the most out of histopathology. It also helps to offer a working list of differential diagnoses.

When addressing chronic feline skin disease, additional ancillary tests may be needed. A CBC and serum chemistry profile will be indicated whenever there is systemic illness present. Radiographs are sometimes useful to identify foreign bodies that are radio-opaque such as bullets or tooth fragments. Unfortunately most plant material will not be identified. Occasionally the use of fistula grams are sought to define the boundaries of a draining tract. Electron microscopy can be useful to identify mycoplasma or L-form bacteria. Special preparation of fresh tissue is superior to tissue prepared for histopathology. Contact your local laboratory for their preferred handling techniques. Although it is expensive, (about $100) electron microscopy can be the deciding factor in differentiating a septic versus sterile disease process.

Whenever chronic draining lesions are present, both anaerobic and aerobic bacterial cultures should be performed. Micro tip culturettes will aid in obtaining a sample from deep within a draining tract. Aseptically prepared skin over a fluctuant pocket will provide an area to collect aspirated samples for culture submission. Additionally, a stab incision can be made to allow the insertion of sterile swabs into the pocket. Many times the best sample is to culture the skin itself. The skin should be aseptically prepared for punch or incisional biopsy. The samples should be sent in sterile Petri dishes or within culturette containers. The addition of sterile saline to the sample is discouraged due to the likelihood of encouraging contaminant overgrowth. If anaerobic cultures are desired from the tissue samples, they must be submitted very rapidly if an accurate diagnosis is to be achieved. Tissue samples should be macerated to aid in recovering bacteria trapped within fibrous connective tissue or tissue grains. Usually this must be requested at the time of submission. To increase your chances of an accurate and rapid diagnosis, inform the laboratory of your differential diagnoses. If Nocardia sp.or atypical mycobacterium are suspected, appropriate agar can be selected that is not routinely inoculated for most submitted specimens. Contact your lab for recommendations on submission of samples for anaerobic or fungal cultures. Many labs require additional samples if these procedures are requested.

A routine cat bite abscess is probably the most common cause of a draining lesion in cats. Anaerobic bacteria are present in the majority of abscesses (Fusobacterium sp., Bacteroides sp., Clostridium perfringens, and Peptostreptococcus sp.)and can be responsible for the odor that is sometimes present. Many aerobic bacteria including Staphylococcus sp., Streptococcus and Pasturella multocida can be present as well. Clinical findings can include draining lesions, fluctuant pockets, or sometimes only acute pain. Diagnosis is based on history and clinical findings. The treatment is usually easy and rewarding. Appropriate drainage and flushing with copious amounts of sterile saline are essential. Various disinfectants can also be added to the lavage solution. A focal area of alopecia or hemorrhagic skin may help to identify the initial puncture site or a location for drainage. Systemic therapy with an antibiotic that has a good spectrum for anaerobic bacteria is usually indicated for 14 days. Good empirical choices would include Penicillin G, Amoxicillin +/- clavulanate, Metronidazole, or Clindamycin. If a lack of response to therapy is seen, then appropriate cultures and evaluation of immune suppressive diseases should be sought. A poor response to therapy may be seen if mycoplasma or other highly resistant organisms are present.

Bacterial folliculitis or furunculosis is a relatively uncommon entity in feline dermatology and is usually seen in older animals. Papules may be present but more typically, crusted papules, crusts, or scaling is identified. Pustules are rarely seen in feline folliculitis. Bacterial folliculitis can be primary but is usually associated as a secondary phenomenon. Predisposing factors can include ectoparasites such as fleas or demodex, allergic dermatitis and trauma associated with pruritus, and nutritional or metabolic disorders. The diagnosis of bacterial folliculitis can be made on clinical findings, evaluation of cytologic preparations, and or histopathology. Phagocytosed bacteria should be present within inflammatory cells. Because Staphylococcus sp. is most commonly found, empirical antibiotic therapy should target this pathogen. Good choices would include Amoxicillin clavulanate, Lincomycin and cephalosporin drugs. Therapy is usually rewarding, however an underlying cause for the folliculitis should be sought.

Nocardia sp. are aerobic, Gram positive, branching bacteria that sometimes stain with acid fast stain. They are ubiquitous within the environment and are opportunist pathogens. Clinical findings are not unique. Chronic abscesses, cellulitis, draining tracts, nodular dermatitis, or hemorrhagic vesicles may be seen. Localized lymphadenopathy may be present. The exudate may contain granules (tissue grains) that are actually colonies of the organism. Diagnosis is based on bacterial culture. Histopathology may be suggestive of Nocardia infection, but organisms are rarely identified even with special stain techniques. Isolation of Nocardia can be difficult due to the fastidious nature of the organism. Swab samples of the exudation and tissue grains, as well as tissue samples should be submitted. It is wise to inform the laboratory that Nocardia is a differential diagnosis as other more rapidly growing bacteria can be discounted as to their importance. Achieving a diagnosis of Nocardia can be difficult and the treatment can be just as frustrating. It is difficult to perform sensitivity testing on Nocardia and in vitro results do not necessarily correlate with in vivo efficacy. Good empirical drug choices include trimethoprim sulfa drugs, Amikacin, and Minocycline. Additional drugs to consider include Marbafloxacin, Amoxicillin clavulanate, clarithromycin and Inipenem. Because of the difficulty in treating this pathogen, multiple drugs should be used concurrently. The prognosis is guarded for a cure and it may take months to achieve clinical remission.

Actinomyces sp. are Gram positive, anaerobic, filamentous bacteria. They do not stain for acid fastness like Nocardia can. Foxtails are a common cause of infections with this organism but Actinomyces may also be found within the oral cavity of animals. The clinical findings are non specific and may include abscesses and draining or ulcerated lesions. Tissue grains may be present within the exudate. The definitive diagnosis is made on anaerobic isolation of this organism and by ruling out other potential causes. Appropriate samples include aspirated exudate or swab collected samples sent in anaerobic culturettes. Because anaerobic bacteria can be difficult to isolate, the laboratory should be notified of your differential diagnosis and samples should be processed immediately. Treatment is usually aided by surgical debridement. Good empirical antibiotics include the penicillins and their derivatives, although other agents that have a good spectrum against anaerobes may be selected. The prognosis is guarded as relapses are common.

Opportunistic mycobacterium are aerobic, Gram positive, facultative pathogens found within the soil. They are not obligate pathogens as other true mycobacterium. Some commonly encountered species are: M. smegmatis, M. fortuitum, and M. cheloneae. These bacteria are positive for acid fast stain due to the high lipid content in the cell wall. Clinical findings can include chronic granulomatous lesions or draining, non-healing wounds. Tissue grains are not present. A definitive diagnosis can be difficult due to the slow growing nature of these bacteria and the paucity of organism usually encountered. Informing the laboratory of your differential diagnosis will allow for the selection of an appropriate mycobacterium agar that will greatly enhance the likelihood of successful isolation. Histopathology will often yield a diagnosis, even in the face of negative cultures. Therapy is usually based on empirical antibiotic selection. However, some labs will perform sensitivity testing on atypical mycobacterium. High doses of fluorinated quinolone drugs administered for several months has been successful in some cases. Baytril has been shown to cause blindness in cats in higher dosages so an alternative drug should be selected. Clofazamine (Lamprene7), a human anti-mycobacterium drug has been helpful in a few cases but is not approved for use in cats. Reversible staining of the skin and tissues may be seen during treatment. The use of concurrent corticosteroid therapy is controversial, although anecdotal reports of improvement have been noted. Aggressive surgical debridement in conjunction with antibacterial agents (many) may also be helpful. A guarded prognosis for cure is warranted.

Classic tuberculosis is an uncommon disease. Clinical findings can include soft fluctuant nodules, plaques, granulomatous lesions and ulceration. Affected patients are usually clinically ill with fever, inappetence, and lethargy. These bacteria are obligate intracellular pathogens and provide zoonotic risk to handlers. Diagnosis is based on isolation of the organisms. Because of the slow growing nature of mycobacterium, isolation and identification can take several weeks, even with appropriate culture media. Histopathology is often helpful because many acid fast rod bacteria can be identified within macrophages of the infected tissues. Treatment protocols developed for human beings and canine patients can be attempted. Euthanasia is usually considered due to the poor prognosis and potential zoonotic risk. When M avium complex is identified, the zoonotic risk is debatable as this is a soil borne pathogen. A combination of doxycycline with clofazamine has been reported to be effective for localized M avium.

L-form bacteria are potentially any bacteria that are partially or completely devoid of a cell wall. Clinical findings can include abscessation and draining lesions, often over joints. Fever, anorexia, and systemic illness are usually present. A common presentation is a bite wound abscess that is poorly responsive to routine therapy. A definitive diagnosis may be difficult to achieve because these bacteria do not grow in culture media very well. Electron microscopy of infected tissue may reveal the presence of L-form bacteria. In many cases, the rapid response to treatment with tetracycline drugs, along with an appropriate history will lead to a presumptive diagnosis. Mycoplasma bacteria are an important differential diagnosis.

Feline Otitis: Diagnosis and Treatment

Feline otitis can be a challenging clinical problem. A commonly used clinical approach to treatment of canine otitis rarely yields satisfactory results when applied to cats. The presentation will focus on common causes of feline otitis. Emphasis will be placed on diverging concepts of treatment between dogs and cats.

Otitis by definition is inflammation of the ear canal, and or the pinna. Otitis externa is a term used when only the external canal, outside of the tympanic membrane, is involved. When the tympanum and the tympanic bulla are involved, the term otitis media is used. Otitis interna implies damage to the hearing apparatus. Neurologic symptoms and deafness are usually present.

Otitis is usually a multifactorial problem. Predisposing factors are those that may allow inflammation to occur. Ear canal stenosis and pinnal deformity are far more common problems in dogs than in cats. High humidity environments or cats that swim frequently are more at risk due to canal tissue maceration. One of the most common predisposing causes of feline otitis is the use of a cotton swab to remove normal ear canal excretions. Some cats have excessively waxy ears and should be left alone.

Primary causes are those that induce otitis directly. Foreign bodies or ectoparasites are the most common causes. Although some allergic cats will have concurrent otitis, this occurs far less commonly than in the dog. Additional primary causes include: autoimmune diseases, neoplasia, and fungal causes. A polyp is usually the result of chronic inflammation. However, in some cases, the presence of a polyp may lead to ear canal inflammation.

The perpetuating factors, bacteria and yeast organisms that are the source of frustration in many canine otitis cases, are infrequently a problem in cats. A polyp is usually a perpetuating factor as a result of chronic inflammation. One of the most important, yet least discussed factor, is the allergic or irritant reaction that occurs after application of topical medications. Anti-inflammatory corticosteroids may be the cause of the reaction. This is counter intuitive considering that these should reduce the amount of inflammation, not be the cause of the problem.

It is possible to quickly limit the differential diagnoses based upon the observation of a unilateral versus a bilateral problem. Unilateral causes are invariably a foreign body, polyp, neoplasia, or trauma (aural hematoma). Bilateral problems are usually parasitic, metabolic (systemic illness), allergic, or autoimmune. Dermatophytosis and bacterial or yeast infections may present as unilateral or bilateral problems.

The proper treatment of feline otitis depends upon an accurate diagnosis. This is no time to guess with a shot of steroids to see what happens. A thorough history is essential. Simple information regarding unilateral versus bilateral problems along with the treatments used are essential starting points. An otoscopic examination is also essential. It is the only way to determine if the tympanum and bulla are involved. It is also the easiest way to find otodectes ear mites and ear masses. Cytology is an important diagnostic tool to evaluate the perpetuating factors. However care should be used in placing swabs into a cat's ear when only brown waxy debris and no inflammation are present. This is often the source of inflammation and further complications! A culture and sensitivity should only be performed for refractory cases or those with highly exudative otitis.

Because many cats may have a metabolic cause of their otitis, additional lab work including CBC, serum chemistry profile, thyroid analysis, FIV and FELV testing may be indicated. Routine radiograph imaging rarely yields useful information. A C.T. scan is better to analyze the extent of the problem when neoplasia or polyps are involved. It stands to logic that any tissue removed from the ear should be sent for histopathologic analysis. When ear biopsy is indicated, the surgeon should be prepared for an extensive procedure including bulla osteotomy. Referral to a boarded surgeon is recommended.

When cleaning the ear canal of the cat, general anesthesia is usually indicated. The author prefers to use nothing other than warmed sterile saline for cleaning cat's ears, even when ear mites are present. Iodine has been shown to be highly ototoxic to cats. Because chlorhexidine has been shown to be ototoxic to dogs, it is a rational leap of faith to avoid this product in cats as well. Besides, there are no licensed products for the ear canal that contain chlorhexidine. I have used on occasion, TRIZ-EDTAŽ and ceruminolytic agents but I tend to avoid anything other than sterile saline for cats.

One of the major differences in the approach to treating otitis in dog from cats involves the usage of topical medications. Topical medications are the mainstay of success in canine otitis. It is my opinion that they should be avoided in treating cats. I have successfully treated refractory otitis in the cat simply by discontinuing the use of topical medications. For undefined reasons, cats tend to develop irritant reactions and true contact allergy reactions in the ear pinna and canal at a significantly higher rate than in dogs (my observations and clinical bias). Also, I have been able to treat many cases successfully without the use of topicals. This is rarely the case in dogs. Lastly, cats hate topical products. Their fastidious nature causes them to frantically remove any topical agent applied to the skin surface. This is a potential source for aural hematoma formation and also for the clients to be wounded by a fractious cat. My advice is to avoid the use of topical medications in the cat!

With that being stated, there are exceptions to the rule. Pyrethrin based ear medications for the treatment of ear mites are very inexpensive compared to other products. They are effective and cheap but the precautions about topical medications should be considered. The topical application of selemectin (RevolutionŽ) is my treatment of choice for resolving ear mites. I use this product every 14 days for three treatments. I strongly recommend this product for monthly usage in general for outdoor cats to avoid ear mites, Notoedres, and heartworm disease. Injectable or orally administered cattle ivermectin is not licensed nor approved for use in the cat for any reason. There is a topical otic suspension consisting of 0.01% ivermectin (AcarexxŽ) that is licensed and approved and highly effective. I strongly recommend using a second treatment for total remission to be achieved. MilbemiteŽ is a topical otic containing Milbemycin 0.1%. Community practice service at TAMU uses this product with perceived excellent results. Very few cases have needed a second treatment. With the highly effective and licensed products available there is no reason to use off-label ivermectin. Any untoward reaction from using cattle formulations of ivermectin will be the responsibility of the clinician.

When bacteria or yeast are perpetuating factors are present in the cat, systemic medications should be used even if the middle ear is not involved. This is absolutely contradictory to my approach to canine otitis. Cats rarely get bacteria or yeast infections except for iatrogenic causes and those associated with ear masses. A good empiric selection of an antibiotic for the cat would include clindamycin (AntirobeŽ) or amoxicillin with clavulanate (ClavamoxŽ) at standard package dosage. Although first generation cephalosporin drugs are very useful in the dog, cats tend to vomit and become anorexic with these products. High dosages of enrofloxacin (BaytrilŽ) should be avoided due to blindness that has occurred in some cats. However, marbafloxacin (ZenequinŽ) may be indicated for usage only if based upon culture and sensitivity. Itraconazole (SporanoxŽ) is the recommended treatment for severe yeast otitis in the cat. The recommended dosage is 10 mg/kg given once daily until a remission is reached. This drug is not licensed for use in the cat and is very expensive. Anorexia and or vomiting may occur. Ketoconazole should be avoided in cats due to hepatopathy. Cats rarely get primary bacteria or yeast infections.

Surgery is indicated for any mass in the ear of a cat. The extent of the procedure is based upon the problem. Appropriate diagnostic procedures including a C.T. scan will help to determine the extent of the disease and can aid the surgeon in giving the owner a reasonable prognosis. This however, depends upon histopathologic diagnosis. There are always potential post-surgical complications to consider. Head tilt or Horner's syndrome due to facial nerve damage may occur. Chronic draining tracts can also be a problem. I recommend a referral to a cat friendly surgeon for most ear surgery. Usually consultations with oncology specialists are available when radiation therapy is part of the ancillary treatment.