Diagnosing and managing ear disease (Proceedings)

Several different diagnostic and medical treatment options exist for treating otitis in dogs and cats. It is important that the veterinarian know all of the options that are available so that they can make recommendations to the pet owner. We will discuss all of the diagnostic and many of the treatment options for otitis.

Diagnostic options

The diagnostic tests that are selected for each patient will vary depending on the chronicity and severity of the ear disease. All cases, even first time cases, should have a cytology and an otoscopic examination (standard handheld otoscope or video otoscope) as part of the work-up. More advanced cases will require bacterial cultures, video otoscopic examination, imaging (bulla series radiographs, CT, MRI), biopsies, and myringotomy. One or more of these diagnostic tests may be necessary.

Cytology

Ear swab cytologies should be performed on every ear case. This diagnostic test takes little time to perform and the amount of information gained is invaluable. Inflammatory cells with cocci most often indicate Staphylococcus spp. or Streptococcus spp. infection. Inflammatory cells with rods often indicate one or more of the following bacteria: Pseudomonas spp., Proteus spp., Klebsiella spp. or Corynebacteria spp. The only two options for the presence of yeast on cytology are: Malassezia spp. (most common) or Candida spp. (rare). Keratin and glandular secretions and no inflammatory cells suggest an endocrine or seborrheic disease. Parasites are easy to find and identify on cytological preparations.

Otoscopic examination

Otoscopic examination is useful for determining whether polyps, foreign bodies, tumors, parasites (ie ear mites or ticks) or ear canal obstructions are present. In addition, an otoscopic examination is required to help to determine whether an ear drum is intact. It is important to know whether an ear drum is intact because the treatment options will be different depending on if the ear drum is present. If the ear drum is not present then ototoxicity is a bigger problem with topical therapies and very few are safe to use in a ruptured eardrum.

Identification of primary lesions on the pinna such as pustules or ulcers can be useful. Pustules on the ears are suspicious for an autoimmune skin disease (ie most likely pemphigus). Ulcers can be present with a severe infection (ie Pseudomonas spp.), drug eruption or autoimmune/congenital skin disease (ie bullous pemphigoid or dermatomyositis, etc).

Video otoscopic examination

Video otoscopic examination has several advantages over using a standard handheld otoscope. The video otoscope has intense magnification which will allow you to visualize the ear canal and ear drum. In addition, images can be taken of lesions or problems within the ear.

Culture

Cultures are most commonly used when bacteria is present in a chronic otitis case. The yeast can be difficult to grow and should be readily found on your cytology. Bacterial cultures are usually not used for first time cases.

The results of the bacterial culture and sensitivity can be useful for helping to select the best systemic therapy. However, treatment choices for topical medications can be limited and the concentrations of drugs used topically are much greater than those used on the sensitivity discs. Therefore, a drug that is not as sensitive on a culture and sensitivity result may work well topically.

Radiographic imaging options

The three different radiographic imaging options that are available are bulla series radiographs, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) All of these imaging options will require general anesthesia or heavy sedation. The owners need to be aware of this situation prior to performing any of these tests.

The least expensive and most readily option that is available in private practice are the bulla series radiographs. Proper positioning is vital to get useful radiographs to evaluate. Lateral, dorsoventral, or ventrodorsal, latero-20 degree ventral laterodorsal oblique and rostro 30 degree ventral-caudodorsal open-mouth oblique radiographs are recommended. The disadvantage is that contrast dye cannot help to visualize soft tissue lesions that might be present.

CT scans are one of the more common diagnostic imaging options used for otitis. This allows you to better visualize the pathology that is present in the bone and soft tissue. Boney involvement would be most likely with an osteomyelitis or a tumor that is lysing the bone. Any soft tissue abnormalities can be better enhanced by using contrast dye.

MRI is more costly than the CT scans. MRI is most beneficial for differentiating central versus peripheral vestibular disease. In addition, the MRI is known to have a more superior contrast resolution of soft tissue than CT scans.

Biopsy

Biopsies of the proliferative skin, tumor, wax plug, or bone are a useful aid for treating difficult ear cases.2,5 General anesthesia is usually required in order to take a biopsy in the ear. Biopsy samples are submitted in formalin to a pathologist for evaluation.

Treatment Options

Ear cleaners

A wide variety of ear cleaners exist either over the counter or through a veterinarian. It is impossible to list all of the different cleaners. Most of these products contain various types of acids (lactic, malic, benzoic, salicylic, acetic, et) and either a cerumenolytic agent or alcohol is added. This author prefers a product containing salicylic acid, lactic acid and propylene glycol (Epiotic®, Virbac). Cleansing/drying solutions can be used with variable frequency (as often as twice daily to as little as monthly). In cases where the animal seems to be overally sensitive to ear cleaners (ie ears become reddened after most ear cleaners), a milder ear cleaner (ie Oticalm®, DVM Pharmaceuticals/IVAX or Oti-clens®, Pfizer) may be beneficial. The author does not use chlorhexidene as an ear cleaner or flush since this topical medication has been reported to more consistently cause ototoxicity.

If wax or a dry scaley ear is the main problem within the ear then a ceruminolytic agent such as Cerumene® (EVASCO Pharmaceuticals) or Cerulytic® (Virbac) are useful. Products contain cerumene which has not been associated with ototoxicity. The main disadvantage of these two otic products is that they are oily. Some owners do not like the oily residue that these products leave after use.

When Pseudomonas spp. is involved in the infection, topical agents that contain tris-EDTA are beneficial. This compound has been shown to help break down the bacterial cell wall of the Pseudomonas organism so that topical medications can more easily penetrate the bacterial cell wall.

Ear flushes

A thorough otic flushing is often necessary to resolve many cases of otitis in small animals. A If the ear infection has gone on longer than 1 month, then an ear flush need to be performed.

Care should be taken when performing ear flushes. Too aggressive of an ear flush can result in excessive head shaking, painful ears, head tilt if the ear drum is ruptured and damage to nerves (ie Horner's syndrome or facial nerve injury). Symptoms of Horner's syndrome include: enopthalmos, ptosis, miosis and protrusion of the nictitating membrane. Facial nerve paralysis is: dropped lip and ear, inability to close the eyelid and decrease palpebral reflex. Vestibular signs (ie head tilt, imbalance, and circling) and deafness may be seen as the result of aggressive flushing or after the use of ototoxic agents that are allowed to remain in the ear.

Several different techniques exist for performing an otic flush. The traditional way to flush an ear is with a bulb and syringe. If this technique is used then care should be taken to make sure that a space exists between the ear and the bulb itself. Too tight of suction can result in the eardrum being ruptured during the flushing.

Commercially available otic flush apparatuses exist. Schering-Plough has the Auroflush® system which is a less expensive ear flushing system that the video otoscope. This apparatus connects up to the sink with a special adapter for the faucet. The disadvantage of this system is that the apparatus is not portable and needs to be used in a particular sink. The other disadvantage is that the ear cones are too large for small dogs and cats. This makes it difficult to get smaller animals ears flushed out properly.

The MedRx video otoscope has an otic flush system (ie Earigator®) that can be purchased. This system is portable (on the same cart as the video otoscope) and has a rheostat so you can adjust the pressure of the water going into the ear.

Ear flushes can be performed with using warm water or by adding something (ie chlorhexidene or betadine) into the water. This author prefers to use water only.

Myringotomy

When an otitis media is suspected, a myringtomy should be performed for both diagnostic and therapeutic purposes. Otitis media should be suspected in the following situations: 1) the animal has chronic, relapsing, or unremitting otitis, 2) tympanic membrane appears abnormal 3) neurologic signs are present and 4)radiographic imaging shows evidence of bulla involvement.

The ear canal should be cleaned prior to performing the myringotomy. A hole is made by using a 5- French polypropylene catheter (open ended tom catheter), spinal needle or carbon dioxide laser using a video otoscope. If a catheter is used, the tip of the catheter can be cut at an angle to make it sharper. The myringotomy incision is usually made on the caudoventral aspect of the pars tensa to avoid damaging the tympanic germinal epithelium and structures of the middle ear. The pars tensa is normally the semitransparent, glistening or pearl gray structure. However, in some cases of otitis media, the pars tensa may appear opaque, bulging, incomplete, or discolored.

After the myringotomy is performed, samples are collected for cytology and for culture. If samples cannot by aspirated easily from the catheter and syringe then you should consider flushing some sterile water into your incision site and using gentle pressure to collect the water flush solution with a syringe.

Topical treatment

A wide variety of topical medications have been used for treating ears in animals. Some are commercially available and others are not commercially available. Some medications are polypharmacy medications that treat more than one condition. Examples of medications that are polypharmacy medications include: Tresaderm® (Merial), Otomax®, (Schering Plough) or its generic or Baytril otic® (Bayer Pharmaceuticals). A limited number of medications treat bacterial skin infections only (ie Gentocin otic®, Schering Plough ). Only one non-otic product has been used consistently to treat yeast ear infections (ie Conofite® 1% solution, Schering Plough ). Several different otitc products exist for treating parasites (ie Acarexx, IVAXX, Milbemite, Novartis and Otomite, Virbac). A topical but non-otic product is labeled for use for ear mites and ticks (ie Revolution®, Pfizer).

Because of the limited number of commercially available otic products, veterinarians have used extra-label products to treat ears. This author has used a variety of ophthalmic solutions in ears with success. If the product is safe enough to go in the eyes then it will be safe enough to go in the ears.

Some veterinarians have made injectable antibiotic medications into otic products. Some examples of injectable antibiotics that have been used as otics are: amikacin, ticarcillin and silver sulfadiazine. Amikacin (Amiglyde, Ft. Dodge) is diluted to a concentration of 30 to 50 mg/ml with sterile saline and used topically in a dropper bottle or syringe. Ticarcillin ( 6 g bottle with 12 ml of sterile water, Glaxo Smith Kline) is reconstituted according to manufacturers label recommendations. This ticarcillin solution concentrate is divided up into 2 ml syringes and stored frozen (remain stable for 3 months). When making the ticarcillin ear solution, mix one of the 2 ml ticarcillin concentrate syringes with 40 ml of normal saline. Divide this solution into four 10 ml aliquots and freeze. The syringes are then stored in the freezer until they are ready to be used. The frozen ticarcillin with maintain stability for 3 months. When you are ready to use the ticarcillin, the syringe is taken out of the freezer and unthawed. This unthawed ticarcillin solution is then stored in the refrigerator in between applications of use for 1 week then discarded.1 Silver sulfadiazine 1% cream (Monarch Pharmaceuticals) has been diluted with a variety of different solutions and used as a topical otic product. However, one study showed that the best and most effective way to compound silver sulfadiazine is with sterile water. Concentrations as low as 0.02% have been shown to be effective against Pseudomonas and Staphylococcus spp. This author prefers using the silver sulfadiazine as a 50/50 mix with sterile water. This more concentrated solution appears to do a better job at treating the yeast along with the bacteria.

Systemic treatment

Bacterial culture sensitivity and MIC results can be useful for trying to determine the best systemic therapy to use. The smaller the MIC number the more sensitive the drug is suppose to be against the organism isolated. It is important to note on the enrofloxacin disc that if the value is intermediate that at a higher dosage such as enrofloxacin 15 to 20 mg/kg once daily (dogs only) may be effective. For difficult cases, extended antibiotic panels are warranted and useful.

If the ear drums are ruptured and yeast is present, then oral antifungal agents are useful. Examples of systemic antifungal agents that have been used to treat yeast otitis include: ketoconazole, itraconazole, terbenifine, and fluconazole (antedoctal reports).

Comments and conclusions

Addressing the underlying cause and treating the infection that is present is essential for properly managing otitis cases. Multiple rechecks are necessary to assess the animal's response to therapy and to help improve owner compliance. Since therapeutic success for topical and systemic ear medications is increased when the bulla and ear are clean, ear flushes are a useful therapeutic procedure to perform. However, the owner needs to be warned that side effects can occur with ear flushes and most dogs will need to be sedated or anesthetized to ensure a deep and thorough cleaning.

After the ears are thoroughly treated, they will need to be treated. Many ear medications exist. Not one medication is appropriate for all ear cases. It is necessary to perform cytologies and otoscopic examinations on every ear case. In more chronic cases, bacterial cultures will be useful for trying to select the best drug to treat a particular case. Both topical and systemic treatment is usually required to treat these chronic cases.

Selected readings

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Marone P, Monzillo V, Perversi L, et. al. Comparative in vitro activity of silver sulfadiazine, alone or in combination with cerium nitrate, against staphylococci and gram-negative bacteria. J Chemother 1988; 10, 17-21.

Gupta AK, Kohli Y, Li A. et al. In vitro susceptibility of the seven Malassezia species to ketoconazole, voriconazole, itraconazole, and terbinafine. Br J Dermatol 2000; 142:758-765.