Tympanometry and Ototoxicity

Principles : This test records the compliance of middle ear system ( Tympanic membrane and ossicles )

Type A = normal  Type As= otosclerosis Type Ad = Ossicular dislocation Type C = Retracted tympanic membrane 

 Stapedial reflex :   On hearing loud sound stapedius contracts . This is for thye protection of inner ear .  Afferent : 8th nerve Efferent : 7th nerve 

 This reflex is absent in 1 ) Deafness 

                                         2) Facial Palsy 

                                         3) Otosclerosis 

 Noise induced hearing loss : It is an occupational disorder . Permissible level of noise 90dB 8 hours a day 5 days a week . 

 Typical finding on PTA : Dip at 4000 Hz in AC and BC curve . 

 Drugs causing ototoxicity are given below : 

Drugs causes high frequency hearing loss in early stages , so high frequency loss in ototoxicity .

 Age induced hearing loss : 

  # a/k/s presbycusis 

  # high frequency hearing loss in early stages . 

  # Cochlear and Retrocochlear or mixed . 

  # Treatment : Hearing aid 

  Sudden SNHL : Sudden hearing loss of min 30 dB which should be visible over at least 3 frequencies of audiometry and should have happened within 3 days . 

   # Mostly unilateral : vascular or viral etiology 

   # DOC : Oral steroid 

    # Other traetment are : 1 ) Transtympanic injection of dexamethasone using microwick 

                                            2) Hyperbaric O2 therapy : Carbogen = 95% Oxygen + 5% CO2 , it                                                  is a vasodilator 

                                            3) Betahistine      (vasodilator) 

  Hearing loss : Wax - 30dB , Glue ear - 10 to 40 dB , Ossicular dislocation with intact tympanic membrane - 54dB , Ossicular dislocation with tympanic membrane perforation 38dB 

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