12843.C09.PGS 3/8/02 11:11 AM Page 253 9 Fitting Strategies for Patients with Unilateral Hearing Loss MICHAEL VALENTE, MAUREEN VALENTE, JANE ENRIETTO, KAREN M. LAYTON Introduction Definition of Unilateral Hearing Loss Patients with unilateral hearing loss typi- For the purposes of this chapter, unilateral cally have difficulty with (1) locating the hearing loss is defined as unaidable hearing sources of sound, (2) understanding speech in one ear and normal hearing [15 dB hear- when the signal arrives on the side of the ing level (HL) or better at 250 to 8000 Hz] in poorer ear, and (3) understanding speech in the opposite ear. Unaidable hearing is de- background noise (especially if the noise is fined as an ear having one or more of the fol- arriving on the side of the better ear). Pa- lowing characteristics: tients with unilateral hearing loss can pres- 1. Profound sensorineural hearing loss so ent a challenge to the dispensing audiolo- that amplified sound cannot be heard gist. The dispenser can choose a traditional with any degree of usefulness. dispensing model, which suggests provid- 2. Very poor word recognition score. ing extensive counseling on the communica- 3. Marked intolerance for amplified tion problems likely to occur as a result of sounds. unilateral hearing loss, or recommend con- tralateral routing of the signal (CROS) am- plification to the good ear. On the other Incidence and Prevalence of Unilateral hand, the dispenser could explore with the Hearing Loss patient several alternate fitting strategies. This chapter focuses on the problems as- Although information is available regarding sociated with unilateral hearing loss and the incidence of unilateral hearing loss in provides information beneficial for dis- children (Bess and Tharpe, 1986; Kielmovitch pensers who want to explore alternative fit- and Friedman, 1988; Oyler et al, 1988; Brook- ting strategies for patients with unilateral houser et al, 1991), there is less information hearing loss. regarding the incidence of unilateral hearing 253 12843.C09.PGS 3/8/02 11:11 AM Page 254 254 STRATEGIES FOR SELECTING AND VERIFYING HEARING AID FITTINGS loss in adults. Much of the information re- (1991) estimated that nearly seven million garding the incidence of unilateral hearing Americans have some degree of unilateral loss in adults involves sudden hearing loss, hearing loss. They quoted a prevalence rate often as a result of illness (Van Dishoeck and for school-aged children of 3:1000 in which Bichman, 1957; Petheram, 1976; Shanon et al, hearing loss was 45 dB HL or greater, which 1982), otologic surgery (acoustic neuroma), increased to 13:1000 if milder losses (26 to 45 or nonotologic surgery (Arenberg et al, 1972; dB HL) were included. They provided no Wright and Saunders, 1975; Plasse et al, 1980; information for children under age 3 years. Millen et al, 1982). The authors reported that Everberg (1960) re- Rambur (1989) reported that the incidence vealed a greater prevalence of unilateral of sudden unilateral hearing loss in the deafness among males (62.3%) than females United States was approximately 40,000 per (37.7%); he also reported a higher rate of left year, equally distributed between males and ear impairment (52.5%). Of interest is that females. Her report and reports by Bye unilateral impairment is generally detected (1978) and Berg and Pallasch (1981) indicate later in life because speech and language that sudden hearing loss usually occurs in skills appear to develop more normally. Of adolescents or older adults, with the greatest Everberg’s 122 subjects, 52.5% were identi- incidence occurring between 30 and 60 years fied after the first year in school. Bess and of age (Megighian, 1986). Hearing loss was Tharpe (1986) cited Tarkkanen and Aho usually unilateral, although Rambur (1989) (1966) to corroborate these findings, with an and Megighian (1986) found bilateral sud- average identification age of 6 years. The den hearing loss in up to 17% of the cases. hearing loss in 50% of the children was not Bergenius (1985) studied vestibular find- detected until 7 years of age or older, which ings in sensorineural hearing loss. Of 1,635 the authors find unacceptable in view of the patients undergoing audiologic evaluation deleterious effects unilateral hearing loss has from 1979 to 1982, 12.9% fulfilled the criteria on academic performance (see below) (Bess for “pure unilateral sensorineural hearing and Tharpe, 1986). loss or tinnitus alone.” Noury and Katsarkas Brookhouser et al (1991) investigated uni- (1989) cited various references that stated lateral hearing loss in children, the results that sudden hearing loss has no sexual of which may lend information related to predilection and a mean age of occurrence adult populations. They also reported an in- between 40 and 47 years of age. Sudden cidence in unilateral hearing loss of 3:1000 hearing loss is usually unilateral, with bilat- when including hearing loss greater than 45 eral involvement reported in 7% of the cases. dB HL or 13:1000 when including hearing Although statistics related to children may loss between 26 and 45 dB HL. They re- not easily be generalized to adults, they may ported that Kinney (1953) found 1307 cases provide general trends. Oyler et al (1988) ex- of sensorineural hearing loss in children, of amined the incidence of unilateral hearing which 48% were unilateral. Of 1829 consecu- loss in a large school district of approxi- tive patients studied by Brookhouser et al, mately 54,000 students, with a second part of 690 (37.7%) had asymmetrical hearing loss. the study looking at academic performance. Of those 690 cases, 391 (56.7%) were described The prevalence of unilateral sensorineural as having isolated unilateral sensorineural hearing loss was approximately 2 students hearing loss. When 67 of these 391 cases per 1000. In 106 children, there were slightly were deleted from the study (due to various more males than females and almost twice as factors, such as conductive component), the many children with hearing loss in the right authors reported on the results of 324 chil- ear as the left ear. Almost three fourths of the dren; 62% were males and 38% were fe- hearing losses were sensorineural (N = 78). males. The left ear was affected in 52% and Bess and Tharpe (1986) and Tharpe and Bess the right ear was affected in 48%. This find- 12843.C09.PGS 3/8/02 11:11 AM Page 255 CHAPTER 9 I FITTING STRATEGIES FOR UNILATERAL HEARING LOSS 255 ing was not statistically significant. The in- (acquired). Congenital unilateral hearing vestigators felt their statistics were consis- loss can be genetic (dominant, recessive, or tent with previous investigators’ prepon- sex-linked) or nongenetic [cytomegalovirus derance of males over females. However, (CMV), low birth weight, syphilis, mumps, previous findings of greater right-sided ver- or anoxia]. In addition, unilateral hearing sus left-sided hearing losses were not sup- loss can be acquired at any age, and the re- ported by this study. sulting hearing loss may be progressive, Tieri et al (1988) observed 280 cases of uni- fluctuating, or sudden. lateral sensorineural hearing loss from 1979 to Several investigators have examined the 1986. The age range was 8 months to 12 years, etiology of unilateral hearing loss in chil- with a mean age at diagnosis of 7.6 years; 62% dren. In each investigation, the cause of the were males and 38% females. They felt these unilateral hearing loss was unknown (idio- findings were in agreement with those of pathic) in the majority of cases. Kinney Tarkkanen and Aho (1966) and Hallmo et al (1953) reported that of known causes in a se- (1986). The right ear was affected in 49.6% of ries of 310 children, meningitis, measles, and cases and the left ear in 50.3% cases. Degree of mumps were the most common etiologies. hearing loss ranged from mild to profound, Tieri et al (1988) examined 280 children be- with 79.3% falling in the latter range. In addi- tween 1979 and 1986 and found that the etio- tion, 250 audiograms revealed a flat configu- logic factor was known in only 23% of the ration. Tieri et al, noting that incidence is diffi- cases, and that of the known factors mumps cult to evaluate, cited the following statistics: was predominant. Everberg (1960) evalu- Everberg (1960), an incidence rate of 0.06%; ated 122 children with unilateral hearing Tarkkanen and Aho (1966), 0.09%; and Kinney loss and noted that congenital factors are (1953), 8.5%. Tieri et al noted that 24.7% of responsible for approximately 75% of the their children were diagnosed before the age cases, with heredity being the major causal of 6 years, as compared with the 47.5% under factor. 7 years noted by Everberg and the 7% before With the recent technologic advances in school age noted by Hallmo et al. They con- the treatment of neonates, additional risk cluded that school age diagnosis may be a factors for unilateral hearing loss have result of critical teacher observation, older emerged. These include persistent pulmo- children’s awareness of sensory skills, and nary hypertension of the newborn (PPHN) exposure to a greater number of infectious (Hendricks-Munoz and Walton, 1988), hy- diseases. perbilirubinemia (Bergman et al, 1985), Although no clear-cut statistic is available intraventricular hemorrhage (Slack et al, regarding the incidence of unilateral sensori- 1986), and low birth weight (Clark and neural hearing loss in adults, perhaps the Conry (1979). Although these factors are findings summarized earlier in this chapter most typically associated with bilateral hear- may provide some insight. The incidence of ing loss, unilateral hearing loss has also been unilateral hearing loss is of such significance reported.