Vestibular recruitment?

[Tom Boismier]

>Does vestibular recruitment actually exist? I have seen several patients
>with  seemingly hypersensitive vestibular systems. Caloric irrigations
>produce nystagmus with SSCs of over 80. I say "over" because the maximum
>measurement my ICS system will measure is 80. Is this significant? Is it
>indicative of pathology?

In our experience, the most common reasons for hyperactive caloric responses 
are (in no particular order): 

calibration error;

a highly-alerted (i.e. anxious...) patient, who panics when symptoms start; 

stimulus error (irrigation time too long, temp too high or low, pressure too 
high);

middle aged patient with hydrops or Meniere's. Studies have reported increased 
SPV of caloric responses in middle age, and in hydrops patients. When you 
combine the 2 factors, it can be pretty impressive.

A true hyperactive response (with the above ruled out) weakly suggests CNS 
involvement, localizing to vestibulocerebellum. I would want confirmation from 
abnormal pursuit ocularmotor testing and/or increased gains on rotary chair 
before I made a big deal of it though...