FELINE OTITIS MEDIA / INTERNA Rod AW Rosychuk, DVM, DACVIM, Colorado State University, Ft. Collins, Colorado

Transcription

1 FELINE OTITIS MEDIA / INTERNA Rod AW Rosychuk, DVM, DACVIM, Colorado State University, Ft. Collins, Colorado Anatomy of the feline middle ear: The middle ear is divided by a bony plate in to two chambers: the dorsolateral cavity (aka tympanic cavity) and the larger ventromedial cavity (aka tympanic bulla). Communication between the two cavities is essentially limited to one small hole at the caudal aspect of the middle ear. Significance: when treating feline otitis media, it is possible to clean the upper ventrolateral chamber, but the ventromedial chamber is not readily available for this purpose. This is why systemic therapy is such an integral part of the management of feline otitis media. Sympathetic nerves arborize over the dorsal ½ of the medial wall of the middle ear. Damage to these nerves produce Horner s syndrome. The facial and parasympathetic nerves run through the very dorsal part of the middle ear. They are encased in a bony channel. In order to see signs of facial paresis and paralysis associated with otitis media in the cat, the pathologic process has to destroy bone. The ossicles of the ear (malleus, incus and stapes) run within the dorsal aspect of the dorsolateral chamber. The two holes in the bone of the medial wall of the middle ear that allow for access to the inner ear include the large round or cochlear window which is slightly dorsal and caudal in the middle ear and the oval or vestibular window which is just dorsal to this. Both are only covered by an epithelial lining, allowing for easy access of inflammatory cytokines, ototoxic drugs, bacterial toxins and bacteria to the inner ear. The cochlea (hearing part of the ear) and vestibular canals are embedded in the petrous temporal bone, just behind these holes. The auditory tube (Eustachian tube) exits the middle ear anteriorly from the dorsolateral chamber and extends rostrally to the posterior pharynx. The middle ear is lined by epithelium. In the dorsolateral chamber this is a respiratory-like epithelium that is pseudostratified, ciliated and contains goblet (mucous producing) cells. In the ventromedial chamber, the epithelium is more squamous. A small amount of serous to slightly mucoid fluid is always being produced by the epithelium of the dorsolateral chamber and moved, by cilia, to the auditory tube, which is also ciliated, out of the middle ear. This is the normal flushing mechanism of the middle ear. The middle ear has a potential normal bacterial flora. At any given time, about 20% of normal feline middle ears can have bacteria cultured from them. In one study (CSU), these included Clostridium sp., Bacterioides sp., E.coli., Corynebacterium sp., Moraxella sp., Avibacterium volantium, Staphylooccus xylosus, Porphyromonas sp, Pasteurella multocida, Stenotrophomonas maltophila, and non hemolytic streptococcus sp.. The auditory tube is usually closed, to prevent the ascent of bacteria/debris in to the middle ear. It opens transiently with chewing, swallowing or yawning to allow air in to the middle ear. This allows for pressure equalization across the tympanic membrane. Pathogenesis of Otitis Media/Interna Inflammation within the middle ear (otitis media, OM) may be infectious (bacterial, fungal and possibly viral) or noninfectious (ceruminous debris; inflammatory polyps, foreign body, neoplasia, trauma). Inflammation within the inner ear (otitis interna, OI) is usually an extension from an otitis media. In the cat, it is relatively common to see evidence of otitis interna along with otitis media. Otitis interna may be seen as a sequel to OM because of extension of bacterial toxins or actual bacterial infection through the round (cochlear) and/or oval (vestibular) windows in to the middle ear. With sterile inflammatory middle ear disease, it would appear that inflammatory cytokines passing through the windows may mediate the development of inner ear signs. It would appear that even marked pressure against the round/oval windows associated with exudate/debris accumulated within the middle ear may produce inner ear symptoms in the cat. This is supported by the observation that myringotomy and flushing of the middle ear on occasion may produce immediate post operative improvement in the signs of otitis interna. Tympanic membrane (TM) perforated: Otitis media may be seen an extension from an otitis externa, through a perforated tympanum. This pathogenesis usually involves the accumulation of ceruminous debris which in turn results in pressure related pars tensa tears. Occasionally this scenario may be seen in ears that are stenotic due to inflammation. With stenosis, accumulated ceruminous debris backs up (because it is not readily able to come out of the ear) and may perforate the TM. A similar pathogenesis may be seen with any mass that completely occludes the canals - such as neoplasia (e.g. ceruminous adenoma or adenocarcinoma, squamous cell carcinoma) or ceruminous cysts. The otitis media may be

2 either infectious (bacterial, Malassezia) or sterile (due to wax/inflammatory debris moving in to the middle ear from the ear canal). Neoplasms (as noted above) that originate from the walls of the ear canal may also extend in to the middle ear to produce an otitis media. On a rare occasion, neoplasia (e.g. squamous cell carcinoma, lymphoma) may originate from the middle ear, perforate the TM and extend in to the ear canal. Tympanic membrane intact: In the following otitis media/interna scenarios, the tympanum is intact, but usually abnormal (thicker, more opaque, discolored, inflamed). Dilatation of the pars flaccida is occasionally seen with more severe accumulations of exudate within the middle ear. In such cases the dilatation is also due to thickening of the tympanic membrane (myringitis). Dilatation of the pars tensa is also possible. 1. Infection extends up a dysfunctional auditory tube that remains more open than it should. This is likely a complication of posterior pharyngeal inflammatory disease (viral infection, chronic bacterial sinusitis). Bacteria are allowed to ascend from the pharynx in to the middle ear. 2. Obstruction due to inflammation within the auditory tube or obstruction due to persistent collapse of the auditory tube related to inflammation or neoplasia of the surrounding tissues. This will result in the accumulation of initially serous to more mucoid secretions within the middle ear (mucoid within 2-4 weeks of obstruction). With obstruction, air within the middle ear is absorbed, creating negative pressure within the middle ear. This facilitates greater fluid absorption in to the middle ear. Fluid accumulation within the middle ear induces an inflammatory response (even without infection) that is often marked (neutrophils, macrophages, lymphocytes). This significant inflammation is seen within 3-4 weeks of obstruction 1. a. With obstruction, negative pressure may be enough to suck bacteria in to a middle ear whose auditory tube is only partially obstructed. The result: an infectious otitis media with inflammation and bacteria seen cytologically. b. With obstruction, if some of the normal bacterial flora of the middle ear happen to be present, it again produces an infectious otitis media (inflammation and bacteria seen cytologically). c. With obstruction, fluid accumulation within the middle ear may be sterile, but still inflammatory (i.e. inflammation, but no bacteria seen cytologically or by culture in the middle ear). 3. An acute otitis media / otitis interna recognized in the cat has been termed Primary otitis media because a cause for the otitis has not been established. To date, cultures from the affected cats usually have not had histories of sinus or pharyngeal disease (to suggest auditory tube obstruction). They are usually presented with acute signs of inner ear disease (head tilt, ataxia, nystagmus). Inflammation within the middle ear is often neutrophilic to pyogranulomatous. The TM is intact, but abnormal (more opaque; occasionally inflamed). The author suspects that at least some, if not most of these cats do have auditory tube dysfunction/obstruction and a pathogenesis that has been outlined above. 4. Inflammatory polyps are most commonly noted in young cats (2 6 years of age; range 2.5 months to 20 years). Although most are unilateral, polyps can be bilateral. Most polyps appear to grow from the epithelial lining of the epitympanic cavity/tympanic cavity (dorsolateral chamber of the middle ear). They often fill the middle ear, then extend either through the tympanum in to the horizontal canal (aural polyp) or down through the auditory canal in to the posterior pharynx (nasopharyngeal polyp). In about 10% of cases, polyps will grow in both directions. On occasion polyps will originate from the lining of the auditory tube, just at the middle ear entrance to the auditory tube and extend in to the posterior pharynx. On a rare occasion, inflammatory polyps will originate from the walls of the horizontal canal. With aural polyps, once the tympanum is breached, secondary bacterial infections within the canal and middle ear are common. Polyps are made up of fibroproliferative inflammatory tissue that is surrounded by a more dense tissue capsule. The etiology of polyps remains unknown. Incidence of otitis media in the cat Otitis media is likely more common than expected. Many cats are sub-clinically affected 2,3. The relatively high incidence of subclinical otitis media was supported by a study in which, of 101 cats with CT evidence of middle ear disease, 34% were considered subclinical. 80% of these had concurrent nasal disease 3. In another study, bulla

3 effusions were seen in as many as 1/3 of cats with sinonasal disease (inflammatory or neoplastic) 4. Bacteria associated with otitis media/interna in the cat: Although there are only a few reports of the bacteria associated with otitis media in the cat, those noted include Pasturella multocida, Beta hemolytic streptococcus, Staphylococcus hominis, Bacteroides sp., Pseudomonas sp., and Streptococcus zooepidemicus. Most bacteria have been shown to be sensitive to Clavamox (good for Pasturella, staph., strep., anaerobes, but not Pseudomonas) and enrofloxacin / marbofloxacin (good for staph., strep., better for Pseudomonas but not good for anaerobes) or pradofloxacin (good for Pasturella, staph., strep, anaerobes, some efficacy for Pseudomonas). Mycoplasma infection of the middle ear was recently reported in 3 cats. Clinical Signs: In cats, the presence of otitis media alone may be associated with head shaking and aural pruritus, depression and occasionally pain on opening the mouth. In some cases of symptomatic otitis media, the first sign to suggest a problem is the development of an acute Horner s syndrome. The most common initial signs associated with an otitis media/interna are actually signs associated with an acute otitis interna : ipsilateral head tilt, asymmetric ataxia and horizontal nystagmus, all of which are peripheral vestibular signs. Some cats may develop both an acute Horner s syndrome and peripheral vestibular signs. Facial nerve paresis or paralysis are seldomly seen because the facial nerve runs through a bony channel in the middle ear of the cat. It would take a lytic process affecting the bone (e.g. osteomyelitis, neoplasia) to affect this nerve. Diagnosis 1. The diagnosis of an otitis media may be made on a clinical basis, by observing a perforated tympanum and the presence of debris within the middle ear. 2. The tympanum may not be able to be seen due to wax/debris accumulation. Especially for chronic otitis and chronic debris accumulation (filling the horizontal canal), even with lower grade secondary infections (staphylococcal and/or Malassezia), there appears to be a higher incidence of perforation of the TM in these scenarios. When approaching empiric therapy, this possibility has to be kept in mind (i.e. necessitating consideration of the use of safer topical therapies in the ears see below). 3. The presence of an abnormal tympanum - thickened, opaque, neovascularized; discolored - suggests the presence of inflammatory middle ear disease. 4. The presence of a dilated pars flaccida +/- pars tensa suggests an otitis media. 5. Radiographs, CT or MRI of the middle ear. CT scan is the gold standard for examination of the middle ear. Inner ear structures are not as well defined. CT not only documents the presence of material within the middle ear, but also helps with therapy / prognosis. The presence of lytic bony changes of the bulla septum / bulla wall suggest the presence of infectious osteomyelitis and would dictate longer term systemic antimicrobial therapy. Severe lytic changes associated with infectious otitis media may warrant consideration for surgical intervention (ventral bulla osteotomy), rather than medical management. Lytic changes within the medial wall of the middle ear (behind which is the calvarium) emphasizes the need to be conservative with middle ear flushing to prevent the forcing of material in to the calvarium. When the etiology of otitis media is unclear and there are severe lytic changes, there would a strong need to rule out neoplasia. Bulla radiographs are not as sensitive for defining the CT changes noted above, but are a reasonable alternative.. 6. Myringotomy recommended when there is a high index of suspicion for otitis media and the tympanum is intact. Higher index of suspicion scenarios: material within the middle ear as seen on radiographs or CT; neurologic signs suggesting otitis media/interna; abnormal tympanum (more opaque; discolored; inflamed; thickened, dilated pars flaccida). Myringotomy procedure: done once the ear has been cleaned and dried; use a 22 gage spinal needle or 5F polypropylene catheter whose tip has been cut to a sharp angle; myringotomy performed caudo ventral on the pars tensa, just above the floor of the horizontal canal. Catheter/needle is passed through the TM until bone is encountered. Sample for both cytology and culture and sensitivity (C+S).

4 Management Considerations: 1. Otitis media associated with infection is dealt with both topical and systemic antmicrobial therapy. Emphasis is placed on the systemic therapy, because the larger ventromedial chamber of the middle ear is not readily accessible to topical therapies. 2. Systemic antibiotic therapy is chosen based on cytology (canals and middle ear) and empirically based on what we know of the bacteria associated with otitis media in the cat. Empiric choices favored by the author would be Clavamox or pradofloxacin (Veraflox; Bayer). Duration of systemic antibiotic therapy usually 4-6 weeks. 3. Systemic antifungal therapy suggested by results of cytology: itraconazole 5 10 mg/kg q 24 hr. Duration of therapy usually 4 6 weeks. 4. Oral glucocorticoid therapy: because of the significant inflammation associated with infectious and non infectious otitis media/interna in the cat, this is often an important part of the treatment : i.e. prednisolone, starting at 1 2 mg/kg/day for two weeks, then mg/kg/day for 2 weeks, then this dose every other day for 1-2 weeks; then ½ this dose for 1 2 weeks. 5. Cleaning the middle ear : Anesthesia required. It will only be possible to clean the smaller dorsolateral chamber of the middle ear. The larger ventromedial chamber is not accessible (only very minimal communication between the two chambers). Emphasis is placed on working within the ventral ½ of the opening to the middle ear to minimize the potential of traumatizing sensitive structures within the middle ear. The hole present in the TM or created (after myringotomy) should be at least 1/3 of the surface area of the pars tensa so that fluid flushed in to the middle ear can be readily flushed out. Gently flush with slightly warm sterile saline through a 5 ½ inch open ended tomcat catheter or 5 F polypropylene catheter or 14 or 16 gage teflon catheter. Flush large volumes of saline through the middle ear ( mls). Suction with the syringe/catheter or through an apparatus that has a method of controlling suction (minimize negative pressure when suctioning within the middle ear). Commercial flushing and suctioning apparatus (e.g. VetPump II; Storz) start at very low flushing pressures (1/8) and low suction settings. Following middle ear cleaning, it is possible to see a Horner s syndrome or signs of peripheral vestibular dysfunction. This is usually the product of excessive manipulation within the middle ear. These signs usually spontaneously resolve within a couple of weeks. It is important to note 6. In the presence of a perforated TM, safer topical medications are used in the ear (will not cause ototoxicity). To initiate therapy ml BID a. For bacteria : injectable enrofloxacin (22.7mg/ml): dexamethasone sodium phosphate (4mg/ml) at a ratio of 1:2 b. For Malassezia : dexamethasone sodium phosphate: 1% miconazole (1:1) c. For bacteria and Malassezia: enrofloxacin:dexamethasone sodium phosphate: 1%miconazole (1:1:2). d. Topical Potent Glucocorticoid - Synotic (fluocinolone and DMSO) +/- enrofloxacin (22.7 mg/ml) 2:1 mix; with this mix, usually initiate therapy with once daily treatment e. Safer Ear flushes: a. Mal-A-Ket Plus (Dechra) ketoconazole, chlorhexidine, TrisEDTA b. Douxo Micellar Solution (Sogeval) Management Scenarios A. Otitis externa, visible perforated tympanum; +/- neurologic signs of OM +/- OI; unable to do anesthesia to sample from middle ear (cytology, C+S) because of cost concerns: 1. Cytology from canals. 2. Topical safe ear solution BID (chosen based on cytology), safer ear flush every other day or every third day (depending on amount of debris in ear). 3. Systemic antibiotic based on cytology - most common considerations would be clavulonate potentiated amoxicillin (Clavamox) or pradofloxacin (Veraflox; Bayer). Duration of therapy 4-6 weeks. 4. Systemic anti-fungal (see above) if Malassezia seen on cytology; duration of therapy 4 6 weeks. 5. Systemic steroid prednisolone see management considerations above for specifics. 6. Recheck every 2 weeks.

5 B. Otitis externa; debris in ear requiring deep ear cleaning; perforated TM found after cleaning, inflammatory debris within middle ear; no neurologic signs 1. Sample for cytology / culture and sensitivity from deep in horizontal canal (before cleaning). 2. As soon as a TM perforation is noted, sample from the middle ear for cytology and C+S 3. Combine samples from canal/middle ear and submit to lab for C+S 4. Gently flush / suction middle ear 5. Based on cytologic findings (i.e. inflammation / bacteria seen on cytology) consider filling the middle ear with an antibiotic : steroid post cleaning (e.g. safer product such as an enrofloxacin (22.7 mg/ml) : dexamethasone sodium phosphate (4 mg/ml) mix 1:2. 6. For at home administration: safer topical steroid/antibiotic/anti-fungal solution BID for 1-2 weeks, then daily for 2 wks, then eod for two weeks; safe ear flush twice weekly. 7. Systemic antibiotic/antifungal based on cytology initially (see A above), then based on culture 8. Systemic steroid (lower end of range; 1 wk at each dose for taper; see Mangement Considerations above). 9. Recheck every 2 weeks. C. Otitis externa with higher index of suspicion of otitis media by extension of debris through tympanic membrane (e.g. ceruminolith in ear); +/- neurologic signs of OM +/- OI 1. General Anesthesia 2. CT or radiographs middle ear 3. Sample from deep within horizontal canal for both cytology and C+S 4. Ear cleaning (canals); when encounter perforation sample from middle ear for cytology and C + S before cleaning the middle ear. Clean middle ear. Continue as for B scenario above. If, after debris removed, TM intact, but high degree of suspicion for otitis media (material in middle ear on radiographs/ct; TM significantly abnormal; neurologic signs) do a myringotomy. If inflammatory exudate found, sample for cytology and C+ S. If inflammatory exudate found, open up a larger hole in the TM (about ¼ to 1/3 of the surface area of the pars tensa caudo ventral portion of the TM; use catheter to do this) and gently flush/suction the middle ear. Infuse an antibiotic/steroid in the middle ear at the conclusion of the procedure 5. Topical and systemic therapies based on cytologic findings (see A and B above). D. Acute signs of otitis media/interna (e.g. acute Horner s and/or signs of otitis interna) canals normal, TM abnormal or unsure. 1. Some clinicians would treat this scenario empirically 5, with no other work up (i.e. no radiographs or CT, myringotomy etc.). Empiric therapy would usually be with a systemic antibiotic and systemic steroid (see A above). The author generally approaches these cases more aggressively: 2. Anesthesia, CT or radiographs of bullae 3. Myringotomy. 4. If inflammatory exudate found within the middle ear cytology, culture and sensitivity testing; open up a larger hole in the ventral / caudo-ventral aspect of the pars tensa of the tympanum and flush the middle ear. 5. Infuse a topical antibiotic/steroid in the middle ear (see B above) 6. Topical and systemic antibiotic and steroid therapy based on cytologic findings (see A ). E. Material seen within the middle ear on radiographs / CT or MRI as an incidental finding, usually as part of a work-up for chronic sinus / pharyngeal problems. Canals of the ear are usually normal; TM may be normal or more opaque than normal or discolored or inflamed. The more opaque, discolored or inflamed the TM, the more likely the fluid is inflammatory. If inflammatory, may or may not be infected. In any case, do a myringotomy. If fluid non inflammatory or only mildly inflammatory, we would not treat. We would assume a more acute obstruction and would look to treat the cause of the obstruction (nasal disease etc. to see if this obstruction could be reversed. If fluid inflammatory, sample for cytology and culture and sensitivity testing. Treat as a potential infectious otitis media (topical and systemic antibiotic, topical and systemic steroid pending cultures). If culture negative, systemic antibiotic therapy can be discontinued. We would, however treat with a full course of systemic steroid (see Management Considerations. Steroid therapy alone can significantly benefit this scenario.

6 F. Primary otitis media/interna this diagnosis is generally made on the basis of rule out i.e. cytologies / cultures come back negative for bacteria (see scenario A ). This syndrome does appear to respond to the empiric therapies generally used for infectious feline otitis media/interna (systemic antibiotic / steroid). It is likely that the systemic steroid is the most important aspect of the therapy for this problem. Prognosis 1. If OM/OI and neurologic signs are acute and therapy is rapidly instituted, neurologic signs often tend to spontaneously resolve within 2 8 weeks. With more chronic neurologic signs, and longer times to institution of therapy, it is very likely that some neurologic signs will persist (e.g. some degree of head tilt). Cats, however, adapt very well to having these defects. 2. Perforations of the tympanum Even large holes within the pars tensa usually will heal (3-6 weeks). If damage to the TM is extensive (i.e.area around the handle of the malleus is not preserved, the TM will not heal. Cats do reasonably well with holes that persist in the TM. Waxy / epithelial debris may gradually fill the dorsolateral chamber and in some cats, this makes them more prone to recurrences of secondary infections in the middle ear. This may warrant periodic (e.g. once yearly) deep ear cleanings. 3. A poor prognosis for the medical management of infectious otitis media is generally given for individuals with severe lytic bulla wall or lysis of the petrous temporal bone as seen on CT. These patients would likely benefit from surgical intervention (ventral bulla osteotomy) or total ear canal ablation if there is significant canal disease. Management of Feline Aural Polyps removal of the polyp by traction/avulsion to just within the hole through the TM (do not try to remove material from deeper within the middle ear). Treat secondary infections (topically and systemically - see above). Mandatory post procedure oral steroid (to shrink back residual polypoid material in middle ear) - prednisolone, beginning at 2-3 mg/kg/day for 2 weeks, then mg/kg/day for 2 weeks, then mg/kg/day for 2 weeks, then mg/kg once every other day for 2 weeks (6-8 weeks of therapy). Success (i.e. failure to re-grow) 95%. References: 1. Keskan N et al. Evaluation of the Middle ear in Cats with Eustachian Tube (Auditory Tube) Obstruction. Abstract 0T03 ACVIM Forum Sula MM, Njaa BL, Payton ME. Histologic Characterization of the Cat Middle Ear: in Sickness and in Health. Veterinary Pathology 2014; 51(5): Shanaman M, Seiler G, Holt DE. Prevalence of Clinical and Subclinical Middle Ear Disease in Cats Undergoing Computed Tomographic Scans of the Head. Veterinary Radiology and Ultrasound. 2012; 53(1): Detweiler D, Johnson LR, Kass PH et al. Computed Tomographic Evidence of Bulla effusion in Cats with Sinonasal Disease: J Vet Intern Med 2006;20: Swales N, Foster A, Barnard N. Retrospective Study of the Presentation, Diagnosis and Management of 16 Cats with Otitis Media Not Due to Nasopharyngeal Polyp. Journal of Feline Medicine and surgery. 2017; 1-5.