Medical Management Of Otitis Media & When To Go To Surgery

LSU SVM ANNUAL DERMATOLOGY SEMINARS
MARCH 2004

Carol S Foil MS DVM Dipl ACVD
Professor of Dermatology
Louisiana State University
School of Veterinary Medicine
Department of Clinical Sciences
cfoil@vetmed.lsu.edu
Dermatology Consultant – Veterinary Information Network

CHRONIC OTITIS EXTERNA

If chronic OE is ceruminous, treat as Dr. Merchant has outlined and look for underlying primary causes.

If chronic OE is purulent, and purulent exudate has been present for more than 6 weeks or if relapses have been occurring more than 6 months, there is >> 50% chance there is otitis media and, even if not, progressive pathologic changes will affect therapy.

PROGRESSIVE PATHOLOGIC CHANGES RECAP

STENOSIS of Horizontal Canal : may be from edema, glandular proliferation, hidradenitis, folliculitis, furunculosis, fibrosis, mineralization of soft tissues.

TYMPANIC MEMBRANE: becomes thickened, may invaginate into middle ear dorsal to manubrium forming false middle ear, may be ruptured.

EPITHELIUM OF TYMPANIC BULLA: may become hyperplastic, metaplastic. May be eroded, scarred; may form inflammatory polyps

EXUDATE INSPISSATED IN MIDDLE EAR: may be mucoid or may be inspissated, may contain hair or keratin debris

BONEY TYMPANIC BULLA: may thicken, develop osteophytes, and, rarely, may develop osteitis.

WHAT DO I DO FOR INITIAL EVALUATION?

• Initial ear evaluation for patency of ear canal, hyperplastic or nodular change in ear canal and palpitation for mineralization of soft tissue. Assess level of pain on manipulation, and if there is pain on opening the mouth.

• Evaluate neurologic status. Signs compatible with otitis media: facial nerve palsy (most common), Horner’s Syndrome (more common in cats), conductive hearing loss; Signs compatible with otitis interna (rare in dogs, more in cats): peripheral vestibular (ataxia, horizontal or rotary nystagmus –fast away from the affected ear, invariant character no matter head position), strabismus, head tilt toward affected side, circling toward affected ear, neurologic hearing loss (as documented with BAER).

• Dermatologic Examination and History: look for signs & compatible with allergy, keratinization defect and, in older patients, endocrinopathy.

• Pre-anesthesia Physical Examination, and other tests as per practice protocols

• Management of Purulent Otitis Always Involves Anesthesia

• Initial Cytology: Expected results C degenerate neutrophils, epithelial cells, Gram negative rods, perhaps RBC=s

• Culture/Sensitivity from ear exudate C disc diffusion sensitivity to start with.

• If no medical contraindication, start prednisone at 1 -2 mg/kg daily.

• Start marbofloxacin at 5.5 mg/kg or enrofloxacin at 20 mg/kg

• Schedule anesthesia for ear flush and possible imaging in 2 C 3 days.

• No topical therapy initially, because these ears are painful!

WHY IS GENERAL ANESTHESIA ALWAYS PART OF THE PLAN (IN MY OPINION)?

1. Otitis Media is a Surgical Disease (more later) and the sooner it is discovered and treated, the better.

2. You cannot expect to remove exudate from the horizontal canal in an awake or sedated animal. In fact, it takes a deeper plane of anesthesia to instrument the horizontal canal than for superficial soft tissue surgery!

3. You cannot thoroughly evaluate the patency and health of the proximal horizontal canal and the tympanum without general anesthesia.

4. . You cannot effectively medicate the proximal horizontal canal with topicals when exudate is present.

WHAT DO I DO WITH THE ANESTHETIZED PATIENT?

• Bulla radiographs or CT or MRI mineralization, stenosis of horizontal canal fluid density in bullae boney changes of bulle

• Initial gentle flush and wipe with warmed sterile saline.

• Final flush and suction visualized with video-otoscope (or use a Fraser tip on a suction device through an otoscope.)

• Evaluate status of horizontal canal, initial responsiveness to corticosteroids.
  
  
  
  

• Evaluate tympanum. Visualization of the tympanum after flushing under anesthesia is the most sensitive test for otitis media.

• If the horizontal canal is not patent enough to allow at least partial visualization of the tympanum, assume it is not present and that there is otitis media.

• If the tympanum is not translucent, assume OM and perform myringotomy.

• The eardrum may be reddened in response to inflammation or from accumulation of blood in the bulla.

• Whitish opacity indicates pus and/or mucus in the bulla and yellow indicates a serous effusion.

• A bulging membrane indicates fluid pressure behind the eardrum.

• Retraction of the eardrum around the malleus indicates a negative air pressure from eustachitis.

• NOTE: Many dogs with otitis externa that have intact eardrums have been shown to have significant bacterial and yeast populations isolated from the middle ear. These dogs may have had a ruptured eardrum that healed, trapping bacteria and yeast in the tympanic bulla. So the presence of an eardrum does not rule out otitis media.
  
  
  
  

• To relieve pressure gradients and to obtain middle ear samples for cytology and culture, a myringotomy should be done. Perform a myringotomy with a 3.5 or 5 french urinary catheter tip cut off. Myringotomy is performed at the 5:00 or 7:00 position in the ventral portion of the pars tensa at the ventral most portion of the attachment of the eardrum to the annulus. Try to aspirate exudate from middle ear

• According to Gotthelf, many veterinary practices are using lasers to make the myringotomy incision. A 0.8mm X 180mm tip can be inserted through the working channel of the Video Vetscope and can be advanced to the eardrum. Applying a pulsed, low wattage (3-4W) laser impulse melts the eardrum. The advantage of laser myringotomy is that the tip does not have to touch the eardrum. In addition, the hole made by the laser takes longer to heal, which is sometimes beneficial in providing drainage.

• If no exudate is aspirated, instill 1 -2 ml non-bacteriostatic warmed saline and aspirate.

• Perform cytology on aspirated exudate or saline flush.

• Perform new culture sensitivity on aspirated material? . (It is reported that organisms recovered from middle ear differ from those from external canal, but I have problems with this study.)

• Flush middle ear with 100 ml of warmed sterile saline, with endotracheal tube cuff inflated. The catheter tip should always be directed ventrally to avoid the auditory ossicles and chorda tympani nerve, which are located dorsally.

• Evaluate for flushed material in the nasopharynx/nares.

• Finish by instilling solution of enrofloxcin 5 mg/ml in Tris EDTA solution. (See Below)

HOW DO I FOLLOW-UP WITH MEDICAL THERAPY?

• 4 - 6 weeks of appropriate systemic antibiotics, IF POSSIBLE.

• 2 - 4 weeks of prednisone at 1 -2 mg/kg.

• Twice daily flush with Tris-EDTA / 5 mg/ml Baytril solution, reducing to once daily.
  
  Note that it it has been shown that it takes 0.5 – 2mls of fluid volume to get to the horizontal canal with the medication.
  
  Recipe for 5 mg/ml enrofloxaxin in TrisEDTA. In 4 oz Tris EDTA, put 6 ml of 100 mg/ml injectable Baytril (Large Animal Strength).
  
  

• Recheck Q 7 – 10 days for 6 - 8 weeks for patency of the ear canal, presence of exudate and cytologic evaluation of status of infection.

• If there is a recurrence of significant exudate, re-anesthetize the dog for another flush and instillation of antibiotic solution. In some patients, particularly when systemic antibiotics cannot be used, weekly bulla infusions of antibiotic may be useful. The patient is given a short acting anesthetic, the bulla is flushed and suctioned, dried, and infused. This procedure is repeated weekly until the ear canal remains dry on the follow up visit. When there is no longer an exudate or secretion, the inflammation of the membrane of the middle ear has subsided.

• During this period is would be good to evaluate for signs of allergy or other potential underlying cause of the severe otitis as well so that the work-up can begin in a timely fashion.

COMMENTS:

1. Formulate an initial prognosis based on the degree of stenosis, nodular hyperplasia and calcification and neurologic status. If any of these is severe or compromised, the ear will not be likely to respond to a medical approach. If the ear is deemed appropriate for surgery (see below) initial medical therapy should be continued up to the time of surgery, but the prednisone should be tapered down prior to surgical referral.

2. Enrofloxacin, ciprofloxacin and marbofloxacin are difficult to compare as to efficacy. There are some dermatologists and pharmacologists who claim that there is data to support superior predicted efficacy with marbofloxacin owing to longer half-life. Others claim superior affordability for cipro even at 20 mg/kg, which is need for comparable efficacy. More data is needed before this issue can be settled.

3. The high dosages recommended for enrofloxacin and marbofloxacin are based on the MIC90 values for Pseudomonas cultures studied.

4. If the cultured Pseudomonas is truly resistant to the fluoroquinolones, then injectable antibiotics may be unitized. We have used either ceftazidime 30?50mg.kg BID; (500 mg vial $7.27) or ticarcillin 60?75mg.kg BID (3gm vial $13). Clients can give these injections at home, SQ for 2 -3 weeks.

5. Alternatives for topical antimicrobials include polymixins, ticarcillin and amikacin.
   

• Polymixins are uniformly effective against Pseudomonas and there are many otic preparations available. However, it is potentially ototoxic and it is VERY expensive to use in the recommended volumes.

• Ticarcillin Recipe for Topical Therapy: 3.1 gm vial in 100 ml saline; aliquot to single doses & freeze; thaw each days two doses each am and warm to room temp before instilling. This is my favorite alternative to fluoroquinolones. Remember each dose should be 0.5 – 2 ml, depending on size of ear.

• Amikacin injectable straight from the bottle is sometimes recommended. CAUTION: like all aminoglycosides, potential for neuro/ototoxicity. I do not use it.

• Silver sulfadiazine mixed 1 part cream with 9 parts water to create a suspension to be instilled in the ear. This is messy and there is a potential for topical sensitization. I do not use it.

6. Tris-EDTA acts as a chelating agent and enhances activity of topical antibiotics against otic pathogens by decreasing stability and increasing permeability of the cell wall. A recent theory to explain resistance patterns in Pseudomonas involves the expression of one or more of three genes, called the MEX genes, selected for in resistant bacteria that cause an "efflux pump" mechanism to activate. The efflux pump causes antibiotics to be actively pumped out of the bacteria. When resistant Pseudomonas have their MEX genes removed, they once again become sensitive to fluoroquinolones. EDTA seems to inactivate these pumps thus restoring the antibiotic sensitivity. In-vitro treatment of highly fluoroquinolone resistant Pseudomonas (MIC>50mcg/ml) with tris-EDTA demonstrated significant reduction in the MIC after a 5-minute treatment

7. Tris EDTA is compounded using 1.2 g EDTA, 6.05 g Tris buffer, 1 L distilled water, pH 8, and autoclaved 15 min. Many compounding pharmacies will prepare solutions for you, but a commercial veterinary preparation is available (TrizEDTA, DermaPet. The ear canal should be filled with the solution 15-30 min before the topical antibiotic every 12 hours if either polymixins or amikacin is chosen. Fluoroquinolones may be mixed into the Tris EDTA.

8. Corticosteroids are used in order to decrease swelling and exudation in the ear canal to improve patency and visualization during the anesthetic procedure. This is the reason for the delay of 2 -3 days (or more) before ear flushing is scheduled. It is generally safe to do this initially in healthy dogs because the majority of the time, the infection is well treated with the empirical choice of fluoroquinolones. Since we have been using this technique and aggressive dosing of fluoroquinolones, we have had no cases where the infection was perceived to have been made worse by this treatment. The corticosteroids are continued for at least 2 weeks in order to reverse the hyperplastic changes in the ear canal and continue to suppress exudation. They should be continued for as long as 4 weeks, if the dog is tolerating this and the infection is coming under control.

9. Bullae radiology requires excellent radiologic technique and positioning. If this is not the standard in your practice, then don=t bother doing them. They are not sensitive for diagnosis of otitis media (estimated only 50% have changes).

10. This is a serious disease that is frequently under-treated in my experience. It is a surgical disease that we can now treat medically IN SOME CASES. It is an expensive disease, and I know of no way to make it less so and still have a chance at a satisfactory outcome. Any and all suggestions in this regard are welcome!

WHAT ARE THE INDICATIONS FOR MORE EXTENSIVE SURGICAL MANAGEMENT IN OTITIS CASES?

• I feel that the aggressive treatment approach outlined here will allow satisfactory resolution without further surgery in approximately 60% of cases of Pseudomonas otitis media, having weeded out the cases with extensive and firm stenosis at the outset. Crunch time comes when stopping systemic antibiotics in 4 -6 weeks. Unresolved otitis media will relapse from the horizontal canal outward.

• If 2- 4 weeks of corticosteroid and antibiotic treatment after myringotomy and flushing have not resulted in patency of the horizontal canal to at least 50% of normal, or the cytology has not become negative for Gram negative rods, the prognosis for avoiding a more extensive surgical approach is not good.

• Relapse at the cessation of antibiotic therapy, failure to resolve during the first 2 - 4 weeks of medical therapy or failure to resolve mild neurological symptoms are indications for bulla osteotomy.

WHAT ARE THE INDICATIONS FOR THE SPECIFIC SURGICAL OPTIONS AVAILABLE?

• Lateral ear canal resection-Lateral ear resection is indicated when medical management is failing to control the infection, but theorizonatal canal is not severely compromised. This is often the result of proliferative changes in the vertical and outer horizontal canal and should not be pursued until a long course of antibiotics and corticosteroids has failed to reduce ear canal stenosis. The only indication for the procedure is to allow easier delivery of topical medications into the horizontal portion of the canal.

• Vertical ear canal resection- is indicated when there is severe narrowing of the vertical canal as above in combination with a reasonably patent horizontal canal. Removal of the vertical canal has the added advantage of eliminating the severely diseased portion of the external canal and allows improved delivery of medication to the remaining canal. The indications are very similar to the indications for lateral ear resection, and the choice is often a matter of surgeon's preference

• Lateral or Ventral Bulla Osteotomy – This procedure is indicated for all cases of medically refractory otitis media. As it costs almost as much as TECA with bulla osteotomy, for practical purposes, this surgery is not as often applied as it should be. It is potentially ear preserving, but if the horizontal canal patency and health cannot be improved by medical therapy, then relapse of OM is guaranteed to ensue.
  
  
  
  

• Total Ear Canal Ablation (TECA) with Bulla Osteotomy. – This is reserved for end-stage ear disease when the health and function of the horizontal canal cannot be restored. It is desirable to avoid this drastic surgery, but in my opinion all dogs with chronic otitis media should have this surgery rather than live with the disease. If we can extrapolate from human experience, otitis media is a painful condition. Dogs with unresolved otitis media are subject to several sources of misery: Pain on opening their mouths, continuous pain from pressure on the tympanum until it ruptures, deep infection of the soft tissue of the horizontal canal. This occasionally results in draining tracts opening on the lateral neck, side of the face. Neurological consequences as discussed above.

• Complications of TECA:

  • Should be discussed thoroughly before referral.

  • Hearing loss-Most dogs with end stage otitis externa have significantly decreased hearing before surgery, and studies using brain stem auditory evoked responses have shown that hearing is usually minimally affected by the surgery. The improvement in quality of life resulting from pain relief far outweighs the significance of any marginal loss of hearing.

• Facial nerve paralysis-Clinically apparent damage to the facial nerve occurs in under 5% of cases. Nerve damage is almost always transient, and usually resolves within 3-4 weeks. Because the facial nerve is responsible for lacrimation, artificial tears should be used during this period.

• Persistent infection-Persistent infection may result from failure to remove remnants of the horizontal canal at its junction with the bulla, or from resistant bacterial infection within the bulla. Pseudomonas spp. are often responsible for resistant infections. Clinical signs may develop several months to years after surgery. These may include a recurrence of any of the common signs of otitis externa, or development of swelling or drainage near the ventral portion of the skin incision. Persistent infection is a rare complication of total ear canal ablation and lateral bulla osteotomy, but it can be extremely frustrating to manage.

WHAT ABOUT OTITIS MEDIA IN CATS?

• Unlike in dogs, ascending middle ear infections is sometimes seen in cats, and may be associated with inflammatory polyps originating in the middle ear or Eustachian tubes.

• The organisms that are prevalent in the upper respiratory tract can gain access to the middle ear as they move up the auditory tube. This occurs from sneezing; the cat forcefully increases the air pressure in the nasopharynx and auditory tube effectively blowing air and organisms toward the middle ear.

• The bacterial organisms causing upper respiratory infections in cats include, Staphylococci, Streptococci, Chlamydia, Mycoplasma, and Bordetella.

• Azithromycin (Zithromax, Pfizer) is being used to treat URI in cats and it has use in the treatment of otitis media caused by these susceptible organisms. Zithromax is an intracellular antibiotic (it achieves very high levels in WBCs and tissue) and has a 48-hour serum half-life in cats. Zithromax is available as a pediatric oral suspension. Each 30 ml bottle contains 1200 mg of dry azithromycin powder. The powder can be measured and re-suspended with sterile water and used as an oral liquid antibiotic. The dose is 5 mg per pound given every 48 hours orally for 2 or 3 treatments.

WHAT ABOUT OTITIS MEDIA AND MALASSEZIA?

• Middle ear disease resulting from yeasts or fungi is rare. Yeast overgrowth is more often seen in “false middle ear” invaginations. If otitis media is documented, systemic antifungal drugs are indicated.

• Oral ketoconazole, itraconazole, or fluconazole can be used to treat middle ear disease. Itraconazole (Sporanox) and fluconazole (Diflucan), although more expensive, may be better at reaching the middle ear from oral administration than ketoconazole. Ketoconazole has recently become available as a generic, so the price has become reasonable. It is supplied in 200 mg tablets. The dose in the dog is 10 mg/kg once daily for 10-14 days, so a 200 mg tablet will dose a 20 kg dog.

WHAT ABOUT THOSE TYMPANI THAT NEVER HEAL?

• Some eardrums will heal only partially and a ring of granulation tissue develops. In most of these patients the bulla will remain dry and the exudation from within the middle ear subsides.

• Potentially ototoxic topical medications and ear cleaners should be avoided in these patients.

• Frequent otoscopic examinations are essential in assessing these patients. If material continues to accumulate in the bulla, suctioning may need to be repeated at weekly or bi-weekly intervals to help remove exudates.