Sunday, January 24, 2010

Clinical pearls in diagnosis of vestibular disorders

1.  Look for nystagmus with and without fixation.  To achieve latter, either examine in a darkened room with Frenzel glasses or use opthalmoscope in one eye and cover the other.

2.  Nystagmus can be assessed with holding eyes 30 degrees from midline in 4 positions (L-R-U-D) each for 20 seconds.  Further out, and nystagmus is expected.  Use a chart to score.

3.  Nystagmus through eyelids can be confused with lid twitch.

4.  Features of central nystagmus that differ from peripheral include pure vertical, horizontal or rotatory rather than combined;  no effect of fixation;  may change direction;  central abnormality may affect pursuit or OKN. In central nystagmus, there may be a null zone near center after which nystagmus changes direction when eyes look in opposite direction.

5.  Head thust sign is a simple test at bedside, of horizontal component.  Move head rapidly a short distance horizontally in one direction and then other.  Eyes should at start be ten degrees from primary position so that after the thrust they will be near primary position.  Patient fixates on examiner's nose.  If there is a catch up saccade in one direction but not the other, that is evidence of a peripheral lesion on that side. The absence of a head thrust sign suggests a central etiology.

6.  Patients with peripheral lesions veer towards the side of the lesion when up.  Patients with central lesions often cannot stand.  Patients with central lesions are more likely to have dysarthria,  numbness or weakness.

7.  Viral labyrinthitis needs to be diagnosed after ruling out other entities.  Bacterial usually has associated mastoiditis that is identified on CT scans of the temporal bone.  Usually auditory and vestibular function both are affected with bacterial infection.

8.  Recurrent episodes that become bilateral and lead to deafness within months are associated with syphilis.

9.  Perilymh fistula often presents abruptly after a precipitating event, such as head trauma, barotrauma, strain while lifting, or sneezing.  It is very common among patients who have undergone stapedectomy for otosclerosis.  Patients with fluctuating symptoms or positive fistula test need to undergo surgery.

10. Very important: the Dix Hallpike test can be positive in central vertigo cases, including tumors, but features are different.  Central variety fails to attenuate with repeated tests, may last longer than 30 seconds, and may have fast phase downward to cheek (as opposed to peripheral which is to bottom ear and forehead). 

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