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Characteristics of hearing loss in patients with herpes zoster oticus

View Article: PubMed Central - PubMed

ABSTRACT

Patients with herpes zoster oticus (HZO) may commonly show symptoms associated with 7th and 8th cranial nerve (CN VII and CN VIII) dysfunction. The aim of this study is to investigate the characteristics of hearing loss in patients with HZO and discuss possible mechanisms.

Ninety-five HZO patients who showed at least one of the symptoms of CN VII and CN VIII dysfunction between January 2007 and October 2014 were included in this study. Hearing loss was defined when the mean thresholds of pure tone audiometry (PTA) in speech frequency (0.5 kHz + 1 kHz + 2 kHz/3) or isolated high frequency (4 kHz + 8 kHz/2) were greater than 10 dB in the affected ear compared with the healthy ear, and a total of 72 patients were classified as the hearing loss group.

The difference of mean PTA thresholds between affected and healthy ears was significantly greater in the high frequency range than in low range (20.0 ± 11.5 dB vs. 12.9 ± 15.7 dB, P = 0.0026) in patients with hearing loss (n = 72). The difference between affected and healthy ear was significantly greater in patients with vertigo (n = 34) than those without vertigo (n = 38) in both the high (P = 0.033) and low (P = 0.024) frequency ranges. In contrast, the differences between affected and healthy ears were not significantly different between patients with facial palsy (n = 50) and those without facial palsy (n = 22) in both the high (P = 0.921) and low (P = 0.382) frequency ranges.

In patients with HZO, hearing loss is more severe in the high frequency range than in the low frequency range. Hearing impairment is more severe in patients with vertigo than in those without vertigo in both the high and low frequency ranges, even though the degree of hearing impairment is not significantly different between patients with and without facial palsy. These findings indicate that the mechanisms of viral spread from CN VII to CN VIII may differ between vestibular and audiologic deficits.

No MeSH data available.


Related in: MedlinePlus

Assumed mechanisms behind the greater severity of hearing loss in the high frequency range compared with the low frequency range in patients with Ramsay Hunt Syndrome. (A) Following viral transmission from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC, if inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn are damaged earlier and more extensively than in the apical turn resulting in more severe hearing loss in the high frequency range. (B) If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve, an outer part of nerve comprising nerve fibers with a high frequency range may be more severely impaired than the inner part according to tonotopic organization of the cochlear nerve.
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Figure 5: Assumed mechanisms behind the greater severity of hearing loss in the high frequency range compared with the low frequency range in patients with Ramsay Hunt Syndrome. (A) Following viral transmission from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC, if inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn are damaged earlier and more extensively than in the apical turn resulting in more severe hearing loss in the high frequency range. (B) If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve, an outer part of nerve comprising nerve fibers with a high frequency range may be more severely impaired than the inner part according to tonotopic organization of the cochlear nerve.

Mentions: Our data demonstrate that the degree of hearing impairment is significantly more severe in the high frequency range than in the low frequency range. Based on the observations that the superior vestibular nerve is directly connected to the facial nerve in the internal auditory canal (IAC),[22] the vestibular deficit in the patients with RHS has been often postulated to be attributed to a direct spread of VZV via neural anastomosis.[5,7,18,19] In contrast, a direct connection between the facial nerve and cochlear nerve has not been reported, even though anastomosis between the cochlear nerve and saccular nerve has been observed.[23] Therefore, cochlear deficit may be caused by viral spread from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC rather than via direction neural connection. If viral inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn would be damaged earlier and more extensively than in the apical turn (Fig. 5A). If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve (Fig. 5B), the outer circumference of the nerve that conveys high frequency range information would be damaged earlier and more extensively than the inner part of the low frequency range. Neural fibers of cochlear nerve are known to be orderly organized according to their frequency.[24]


Characteristics of hearing loss in patients with herpes zoster oticus
Assumed mechanisms behind the greater severity of hearing loss in the high frequency range compared with the low frequency range in patients with Ramsay Hunt Syndrome. (A) Following viral transmission from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC, if inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn are damaged earlier and more extensively than in the apical turn resulting in more severe hearing loss in the high frequency range. (B) If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve, an outer part of nerve comprising nerve fibers with a high frequency range may be more severely impaired than the inner part according to tonotopic organization of the cochlear nerve.
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Figure 5: Assumed mechanisms behind the greater severity of hearing loss in the high frequency range compared with the low frequency range in patients with Ramsay Hunt Syndrome. (A) Following viral transmission from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC, if inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn are damaged earlier and more extensively than in the apical turn resulting in more severe hearing loss in the high frequency range. (B) If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve, an outer part of nerve comprising nerve fibers with a high frequency range may be more severely impaired than the inner part according to tonotopic organization of the cochlear nerve.
Mentions: Our data demonstrate that the degree of hearing impairment is significantly more severe in the high frequency range than in the low frequency range. Based on the observations that the superior vestibular nerve is directly connected to the facial nerve in the internal auditory canal (IAC),[22] the vestibular deficit in the patients with RHS has been often postulated to be attributed to a direct spread of VZV via neural anastomosis.[5,7,18,19] In contrast, a direct connection between the facial nerve and cochlear nerve has not been reported, even though anastomosis between the cochlear nerve and saccular nerve has been observed.[23] Therefore, cochlear deficit may be caused by viral spread from the facial nerve into the cerebrospinal fluid (CSF) or perilymph within the IAC rather than via direction neural connection. If viral inflammation spreads from the IAC to the cochlea through CSF and perilymphatic fluid, tissues in the basal turn would be damaged earlier and more extensively than in the apical turn (Fig. 5A). If viral spread from the CSF occurs across the perineural tissue of the cochlear nerve (Fig. 5B), the outer circumference of the nerve that conveys high frequency range information would be damaged earlier and more extensively than the inner part of the low frequency range. Neural fibers of cochlear nerve are known to be orderly organized according to their frequency.[24]

View Article: PubMed Central - PubMed

ABSTRACT

Patients with herpes zoster oticus (HZO) may commonly show symptoms associated with 7th and 8th cranial nerve (CN VII and CN VIII) dysfunction. The aim of this study is to investigate the characteristics of hearing loss in patients with HZO and discuss possible mechanisms.

Ninety-five HZO patients who showed at least one of the symptoms of CN VII and CN VIII dysfunction between January 2007 and October 2014 were included in this study. Hearing loss was defined when the mean thresholds of pure tone audiometry (PTA) in speech frequency (0.5 kHz + 1 kHz + 2 kHz/3) or isolated high frequency (4 kHz + 8 kHz/2) were greater than 10 dB in the affected ear compared with the healthy ear, and a total of 72 patients were classified as the hearing loss group.

The difference of mean PTA thresholds between affected and healthy ears was significantly greater in the high frequency range than in low range (20.0 ± 11.5 dB vs. 12.9 ± 15.7 dB, P = 0.0026) in patients with hearing loss (n = 72). The difference between affected and healthy ear was significantly greater in patients with vertigo (n = 34) than those without vertigo (n = 38) in both the high (P = 0.033) and low (P = 0.024) frequency ranges. In contrast, the differences between affected and healthy ears were not significantly different between patients with facial palsy (n = 50) and those without facial palsy (n = 22) in both the high (P = 0.921) and low (P = 0.382) frequency ranges.

In patients with HZO, hearing loss is more severe in the high frequency range than in the low frequency range. Hearing impairment is more severe in patients with vertigo than in those without vertigo in both the high and low frequency ranges, even though the degree of hearing impairment is not significantly different between patients with and without facial palsy. These findings indicate that the mechanisms of viral spread from CN VII to CN VIII may differ between vestibular and audiologic deficits.

No MeSH data available.


Related in: MedlinePlus