Biology Reference
In-Depth Information
cise and, for most purposes, probably best replaced by a simple description
of age of onset (e.g., onset in adolescence, third decade, etc.).
Except in cases of congenital profound deafness, the temporal course of
the hearing impairment is also described. Hearing loss may be stable or
progressive, and progression is often observed in association with dominant
inheritance of hearing loss (Table 6.1). Fluctuation may be present in other
types of hearing loss, such as that associated with recurrent otitis media or
Meniere's disease (see
DFNA9
, 3.7.2). Fluctuating or incremental hearing
loss may also be associated with head trauma or congenital inner ear mal-
formations such as Mondini dysplasia or enlarged vestibular aqueducts, or
a combination of these two factors (Jackler and De La Cruz 1989; Leven-
son et al. 1989; Schuknecht 1980). These inner ear malformations sometimes
have a genetic basis, as there have been several reports of familial cases
(Abe et al. 1997; Chan et al. 1991; Griffith et al. 1996; Griffith et al. 1998).
2.3 Temporal Bone Histopathology
Inner ear neurosensory tissue for histologic examination is almost never
accessible in the living patient. Therefore, histopathologic studies of post-
mortem human temporal bone specimens can be helpful for correlating
anatomic and histologic findings with clinical observations in the myriad
disorders affecting auditory and vestibular function (Schuknecht 1993).
However, it has been difficult to derive broad conclusions about the patho-
genesis of hereditary hearing loss due to the paucity or absence of speci-
mens for many of the disorders, as well as artifactual changes arising from
delayed or inadequate preservation of the specimens.
FIGURE 6.2. Pure-tone audiograms: (A) Bilateral conductive hearing loss associated
with bilateral otitis media; (B) Bilateral high-frequency sensorineural hearing loss
due to noise exposure, demonstrating a typical “noise notch” at 4,000 Hz; (C) Uni-
lateral moderate to profound sensorineural hearing loss in a patient who received
intratympanic gentamicin (aminoglycoside therapy); (D, E, F) Differing patterns of
sensorineural hearing loss in three affected members of a single kindred segregat-
ing Waardenburg syndrome. Panel D illustrates a unilateral low-frequency hearing
loss, panel E illustrates a symmetric, fairly flat mild to moderate loss, and panel F
shows a profound right-sided loss with a left-sided, mild to moderate high-frequency
loss. SRT is the speech reception threshold, the softest level at which a person can
understand 50% of spoken words. SDS is the speech discrimination score, the per-
centage of word stimuli that are perceived correctly. Although bone conduction
thresholds are not shown in B and E, previous audiometric evaluations on these
patients had demonstrated that the hearing loss was sensorineural, with no signifi-
cant difference between bone- and air-conduction thresholds. Reliable speech dis-
crimination scores were not obtained as part of the evaluations shown in C and E
due to the young age of the patients.
