12843.C10.PGS 3/8/02 11:12 AM Page 272 10 Fitting Strategies for Patients with Conductive or Mixed Hearing Loss JOEL GOEBEL, MICHAEL VALENTE, MAUREEN VALENTE, JANE ENRIETTO, KAREN M. LAYTON, MARK S. WALLACE Introduction Bone conduction aids were once the main- stay of amplification technology for CHL. Surgical correction of conductive hearing These bone conduction devices, however, loss (CHL) is the principal and preferred have been superseded by newer technology treatment by most patients. Surgical therapy [i.e., bone-anchored hearing aid (BAHA®)]. is successful in the majority of cases, but not The use of conventional or programmable all patients are candidates for surgery be- air-conduction aids and implantable bone- cause of medical, anatomic, or personal rea- conduction hearing devices is emphasized sons. Although most who undergo an oto- in this chapter. logic operation achieve socially adequate There are a variety of causes of hearing hearing [i.e., speech recognition threshold loss. It is important for all members of the (SRT) of 25-dB hearing level (HL) or less], hearing health care team (otolaryngologists, some do not, and these patients can gener- audiologists, and aural rehabilitation spe- ally obtain additional benefit from amplifica- cialists) to fully understand the mechanisms tion. In cases of CHL in only hearing ear, the of both conductive and sensorineural com- surgeon recommends amplification to avoid ponents in each individual case and develop the risk of surgical complications that might an optimal rehabilitative strategy. In cases increase the hearing loss, provided that the with a significant conductive component, CHL is not the result of a progressive disor- many factors must be weighed. Certain der, such as a cholesteatoma. Thus, amplifi- physical findings such as persistent otor- cation for CHL remains a topic of great inter- rhea, cholesteatoma, and mass lesions of the est to audiologists, otologists, and patients external and middle ear require aggressive alike. medical and surgical therapy regardless of This chapter discusses the types of CHL the degree of conductive impairment. In for which amplification is the primary other cases with congenital or progressive treatment method, those for which amplifi- disorders resulting in CHL, the main issues cation is fitted secondarily following recov- are the degree of hearing impairment, the ery from surgery, and those for which com- age of the patient, the status of the other ear, bined surgical-audiologic treatment (i.e., and the probable success of surgery versus implantable hearing device) is warranted. amplification. 272 12843.C10.PGS 3/8/02 11:12 AM Page 273 CHAPTER 10 I FITTING STRATEGIES FOR CONDUCTIVE OR MIXED HEARING LOSS 273 This chapter first outlines the various migration of cerumen. Some patients suffer causes of CHL and then reviews the medical, from excessive collections of squamous de- surgical, and rehabilitative options. bris that forms a plug or cast of the EAC. If the process does not erode the skin or bone of the EAC, the term keratosis obturans ap- Lesions of the External Auditory Canal plies. In cases of canal erosion, a canal wall Any process that obstructs the external audi- cholesteatoma is suspected. Periodic re- tory canal (EAC) can result in a CHL up to moval of the debris is indicated and possible 40-dB HL. These lesions can be separated surgical widening and grafting of the EAC is into congenital or acquired etiologies. Congen- performed in severe cases (Farrior, 1990). ital stenosis (narrowing) or atresia (failure to Tumors of the external canal may be either develop) of the EAC may be partial or com- malignant or benign and either soft tissue or plete and is frequently accompanied by de- bony. Keratinous cysts of the EAC are com- formities of the pinna, ossicles, middle ear mon and warrant surgical removal if they cavity, and otic capsule, resulting in a wide obstruct the canal. Malignant tumors include range of hearing loss from mild conductive squamous cell, basal cell, melanoma, cerumi- loss to severe mixed loss. High-resolution noma, and tumors of the parotid gland in- computed tomography (CT) scan of the tem- vading the EAC. Surgical therapy is the main poral bone is necessary to evaluate the extent treatment for these lesions. Acquired bony of bony versus soft tissue stenosis, the shape lesions include exostoses and osteomas, which of the ossicular chain, and the presence or ab- are also removed when they obstruct the sence of an aerated (air-containing) middle canal or trap wax and debris (Fisher and ear space. Surgical reconstruction of the EAC McManus, 1994). and ossicular chain is warranted as early as Chronic external otitis may lead to pro- possible in cases of bilateral stenosis with CT gressive narrowing of the external canal with evidence of middle ear aeration and normal subsequent hearing loss. Aggressive topical otic capsule anatomy (Chandrasekhar et al, steroid and antimicrobial therapy is neces- 1995). In cases of unilateral disease, patients sary, with surgical treatment reserved for are usually advised to reach adulthood be- cases of soft tissue stenosis (Parisier and Lev- fore making a decision regarding surgery. enson, 1991). The use of hearing aids in these Amplification strategies include bone-conduc- cases is contraindicated because of the aggra- tion hearing aids and bone-anchored hearing aids vation of the inflammation caused by the de- (BAHAs) in cases where reconstruction of the vice in the EAC. EAC and ossicular chain is impossible. These two treatment plans are discussed later in this chapter. Lesions of the Tympanic Membrane Acquired obstruction of the EAC is com- Tympanic Membrane Perforation monly caused by cerumen impaction, collec- tion of squamous (skin) debris, tumors, or Perforations of the tympanic membrane chronic external otitis (infection) with steno- cause a variable amount of CHL based on sis. Periodic cerumen removal in the office the size and location of the perforation and under direct vision is required in certain pa- the presence or absence of otorrhea. Small tients with excessive cerumen production or (1 to 2 mm) dry perforations generally cause small, tortuous external canals. Self-manipu- minimal hearing loss (in fact, this is essen- lation of the canal (i.e., cotton swabs) is not tially identical to the placement of a pres- recommended due to the possibility of in- sure-equalizing tube). Larger perforations jury to the canal skin or tympanic mem- with chronic mucoid otorrhea centered more brane. This problem is especially bother- posteriorly tend to cause more CHL in the some in patients wearing hearing aids that 25- to 35-dB HL range. Total tympanic mem- occlude the canal and prevent the normal brane perforations can result in CHL of 12843.C10.PGS 3/8/02 11:12 AM Page 274 274 STRATEGIES FOR SELECTING AND VERIFYING HEARING AID FITTINGS 40-dB HL or greater. When the perforation is ate CHL. Placement of long-standing PE posterosuperior, extends to the margin of tubes for ventilation is the mainstay of ther- the tympanic membrane, and collects squa- apy (Mandel et al, 1989). Chronic otorrhea via mous debris, a cholesteatoma is suspected a TM perforation is common and precludes that may cause ossicular erosion and hear- the use of a hearing aid until the drainage ing loss as great as 60-dB HL. is stopped via medication or tympanomas- In most cases, surgical repair of the perfo- toid surgery. Finally, ossicular continuity is ration is recommended and is successful in frequently disrupted at the incudostapedial about 90% of cases with near-complete clo- joint, resulting in CHL from 15- to 50-dB HL. sure of the air-bone gap (Glasscock, 1973). In In these cases, ossiculoplasty with bone or a small percentage of cases, surgical failure synthetic prostheses is indicated with vari- or late reperforation occurs due to poor eu- able success (Brackmann et al, 1984). In many stachian tube function. In such cases, ampli- instances, amplification is necessary due to a fication is indicated as long as the perfora- persistent conductive loss or an accompany- tion is dry. ing sensorineural component. Tympanosclerosis Cholesteatoma Tympanosclerosis is the accumulation of As mentioned above, cholesteatoma is an dense hyaline-like material in the fibrous aggressive invasion of squamous epithelium layer of the tympanic membrane. This results into the middle ear and mastoid spaces. Al- in stiffening of the tympanic membrane and though not truly neoplastic, the squamous may impede sound transmission. In severe cells incite a cascade of inflammatory media- cases, the ossicular chain is also involved. tors that trigger bony resorption involving Surgical management is warranted when a the ossicles, mastoid cells, and even the otic perforation is also present; otherwise, ampli- capsule. In all cases, surgical removal or ex- fication is recommended to overcome the teriorization of all cholesteatoma matrices is CHL. necessary to achieve a dry ear (Parisier et al, 1991). When this is done, then either surgical Adhesive Otitis Media reconstruction of the ossicular chain or am- plification can be achieved. Cholesteatoma In certain cases of severe eustachian tube is an aggressive process with serious com- dysfunction, the tympanic membrane (TM) plications and therefore must be treated collapses into the middle ear space. A mod- aggressively. erate conductive loss is common and surgi- cal attempts to graft the TM with fascia or Otosclerosis cartilage and placement of a pressure equal- ization (PE) tube are variably successful. In Otosclerosis is a progressive osteodystrophy such cases, amplification is recommended to (abnormal bone growth) of the otic capsule rehabilitate the ear. that most frequently involves the anterior stapedial footplate, causing fixation and pro- gressive CHL. The disease is thought to be Lesions of the Middle Ear and Mastoid inherited in an autosomal-dominant pattern with variable penetrance, although alterna- Chronic Otitis Media tive theories implicating viral infections have Chronic infections of the middle ear can re- been reported.