deafness_sensorineural

sensorineural hearing loss / deafness

aetiology

transient noise-induced hearing loss

  • prolonged acute exposure to loud noise results in transient reduced hearing
  • this may be due to depletion of calcium stores within the tectorial membrane of the cochlear which appears to regulate hearing by release calcium ions 1)

noise-induced deafness

  • usually effects high frequencies primarily, particularly around 4000Hz, although later all frequencies become affected
  • ~20% of adolescents in Western cultures have noise-induced deafness
  • OH&S recommended levels:
    • hearing protection if exposed to > 85dBA
    • < 8hrs at 85dBA (eg. power lawn mower)
    • < 4hrs at 88dBA
    • < 2hrs at 91dBA
  • recommended portable device volume levels listening to music using earphones based upon NIOSH standards:
    • < 4.6hrs / day at 70% maximum level
    • < 1.2hrs / day at 80% maximum level
    • less if other risk factors such as ototoxic drugs
  • a short blast of loud noise also can cause severe to profound SNHL

ototoxicity

degeneration in old age

endolymphatic hydrops

migraine

conditions affecting the acoustic nerve

sudden sensorineural hearing loss (SSNHL)

  • acute unexplained sensorineural hearing loss of at least 30 dB over at least three test frequencies occurring over less than a 72hr period
  • >90% are unilateral
  • many present with a sensation of a blocked or full ear
  • 90% have tinnitus
  • most are idiopathic ?role of Herpes simplex virus (HSV) as with Bell's palsy
  • recovery is often spontaneous
  • can occur at any age but peak is around 50yrs
  • incidence 2 to 20 per 100,000 people per year
  • associations:
    • increased serum levels of fibrinogen and homocysteine
    • genes related to prothrombotic states (particularly MTHFR polymorphisms)
    • bilateral SSNHL:
  • Ix and Mx:
    • otoscopy to exclude local causes
    • audiometry
    • MRI scan with gadolinium to exclude other causes of unilateral hearing loss, such as acoustic neuroma, perilymphatic fistula, Meniere disease, vascular insufficiency, multiple sclerosis, or other conditions involving the central nervous system, although MRI is likely to be normal in over 90%
      • of those with only mid-frequency loss, 1/3rd may have a retrocochlear tumor
      • stroke (CVA) involving anterior inferior cerebellar artery (AICA) which feeds the internal auditory artery, may cause sudden hearing loss with ipsilateral Horner syndrome, diplopia, nystagmus, facial weakness, limb clumsiness, ataxia, and contralateral loss of pain or temperature sensation.
    • 10-14 days high dose corticosteroids is often tried but efficacy is unproven
    • antiviral agents are generally not used as do not appear to be useful
    • oral magnesium and zinc may have a role but very small studies
  • prognosis:
    • 2/3rds will have some recovery although only 25% of those with profound hearing loss will have some recovery
    • those who have not improved within three months will generally not recover significantly

other causes

  • congenital viral infections (eg. rubella, CMV, toxoplasmosis, syphilis)
    • hearing loss is often delayed and progressive
  • congenital malformations of the inner ear
    • Michel / Mondini / Scheibe / Alexander
  • viral cochleitis
  • surgery
  • barotrauma
  • penetrating trauma
  • autoimmune diseases
  • complication of Kawasaki disease
  • prematurity especially birth weight < 1500g (incidence 1 in 200)
  • neonatal jaundice

genetic causes

  • 1 in 2000 children have hereditary sensorineural hearing loss (SNHL)
  • genetic causes account for almost half of children with SNHL
  • 1/3rd of these are associated with syndromes
  • 80% are autosomal recessive such as:
    • Usher syndrome
    • Pendred syndrome
    • Alport syndrome - mainly in the 2000 to 8000 Hz range
    • Jervell-Lange-Nielsen syndrome (long QT syndrome with deafness)
    • > 80 distinct loci have been linked with nonsyndromic recessive hearing loss
  • 15% are autosomal dominant including:
    • Waardenburg syndrome types I and II
    • neurofibromatosis I and II
    • branchio-oto-renal syndrome
    • velocardiofacial syndromes
    • Williams-Beuren syndrome (WBS) - mild to moderate high-frequency sensorineural hearing loss in adulthood
    • > 60 loci have been mapped and over 25 genes have been implicated in nonsyndromic AD hearing loss
  • 2% are X-linked
    • Hunter syndrome (mucopolysaccharidosis 2)
    • X-linked congenital SNHL
    • early onset progressive sensorineural hearing loss
  • 1% are mitochondrial
deafness_sensorineural.txt · Last modified: 2019/03/11 07:13 by gary1