3. Abnormal Abr

Front 1

How are norms for ABR based?

Back 1

on stimulis parameters (intensity, click rate, etc)

Front 2

Back 2

know

Front 3

What are the general findings for ABRS in conductive losses and why?

Back 3

All waves are pro prolonged, including wave I, however interweave latencies are well within normal limits

this is because the conductive component reduces the stimulus intensity in the cochlea, however once it reaches the cochlea, a normal ABR is seen

Front 4

How does otitis media affect the ABR?

Back 4

• wave 1 prolongation in cases of OM
• After OM resolves, waves typically return to normal
• chronic OM may have long term effects on ABR (even after hearing returns to normal)
• suggestive of slightly abnormal brainstem processing in groups with long term OM

Front 5

What are the general findings in ABRs with HFSNHL?

Back 5

• small and poorly formed wave I with slight latency delay
• interwave latencies are WNL
• with decreased stimulus intensity, wave I will disappear, then wave V

Front 6

How is ABR affected by cochlear HL?

Back 6

Wave V latency & waveform morphology are progressively affected by

• greater degrees of peripheral HL
• increased sloping HL

normal wave V latencies have been recorded in pts with

• meniere's disease
• HL up to 60 dB HL

Front 7

How is ABR affected by degree of cochlear HL?

Back 7

• w HL up to 35 dbHL, ABR should not be affected
• HL exceeding 50 dBHL @ 4 kHz, wave I is often absent
• HL 50-70 dBHL @ 4 kHz, abnormal ABRs are often expected

Front 8

How should you modify the stimulus based on the amount of HL?

• 0-10 dBHL
• 20-39 dBHL
• 40-59 dBHL
• 60-79 dBHL

Back 8

Front 9

What is the general rule for modifying stimulus based on the amount of hl?

Back 9

present at least 20 dB higher than the threshold in the 2-4 kHz region

Front 10

What are some ways to increase wave I identification in cochlear HL?

Back 10

• decreasing stimulus rate
• increasing stimulus intensity
• use ear canal (tiptoed) or tympanic electrode
• run simultaneous ecochg and ABR

Front 11

What are the general findings in ABRs with retrocochlear disorders and why?

Back 11

wave I is present with normal latencies, however there is a delay in latency between wave I-III

because the response is reflecting transmission of auditory signal along the VIII cranial verve

Front 12

What are possible occurrences with ABR and retrocochlear disorders?

Back 12

• prolongation of absolute latencies
• prolongation of interweave latencies
• degradation of waveforms
• absence of waves (especially later waves)

Front 13

What are potential disorders associated with these retrocochlear findings?

Back 13

vestibular schannomas (aka, acoustic neuromas, neurinomas, neurilemmomas)

neoplasms (meningiomas and gliomas)

positive identification of large tumors (~2cm and up) - ~92-98% positive ID (small tumors often missed)

Front 14

So if the ABR doesn't catch the retrocochlear, what will?

Back 14

MRIs with Gd-DTPA - the gold standard in identifying cerebellopontine angle tumors

allows for ID of tumors as small as 0.3 cm x 0.3 cm

Front 15

abnormal ABRS may be seen in patients with what neurological disorders?

Back 15

• multiple sclerosis
• parkinson's disease
• global cerebral insults
• comatosed pts (w head trauma)
• albinism (misrouting of auditory pathways)

Front 16

How is ABR in those with auditory neuropathy?

Back 16

puts display disorder at the level of inner hair cells and/or auditory nerve

typically bilateral

• have been cases of asymmetries between ears
• few cases of unilateral symptoms

Front 17

Back 17

...

Front 18

Back 18

...

Front 19

What should you consider when seeing this?

Back 19

• accurate marking of the waveform is essential (minor inconsistency could determine normal vs abnormal)
• age of patient (more normal result if person is older)
• gender (more normal for a male than female)
• temperature (mild hyperthermia would make this a normal finding
• Is the finding bilateral or unilateral

Front 20

What if this is a unilateral finding?

Back 20

characteristic of a TUMOR related to auditory dysfunction in the region of the VIII nerve or lower brainstem (cerebellopontine angle)

Front 21

What if this is a bilateral finding?

Back 21

its a characteristic of brainstem (pons) dysfunction

less common of a bilateral VIII nerve dysfunction (neurofibromitosis)

Front 22

What could be going on here?

Back 22

• prolongation is mainly due to extend wave IV-V
• suggests rostral brainstem auditory dysfunction
• often bilateral
• serious finding in pots with hydrocephalus, increased intracranial pressure or other dynamic neuropathy (indicates compression in upper brainstem)

Front 23

What's going on here?

Back 23

• poor waveform morphology
• poor reliability
• may reflect asynchronous neural function or neuropathy
• in a healthy person, may suggest MS

Front 24

What could be going on here?

Back 24

unusual occurrence

check patient characteristics and rerun

Front 25

What's going on here?

Back 25

sign of severe brainstem dysfunction

clear waves I and II rule out serious auditory problem