I think that the occurrence of vestibular decompensation is often overlooked during balance assessment. What are some guidelines for identifying the presence of decompensation, especially if no previous vestibular testing was performed? What are causes or conditions that would elicit decompensation? When decompensation occurs has the cerebellar clamp been reactivated? What are suggestions for patient management if the presence of decompensation is identified?
I agree that vestibular decompensation is often overlooked during balance assessment, as there is nothing in the standard ENG/VNG battery that gives you any useful information about the patient's level of central compensation, and no information about the patient's functional abilities. Here is a scenario where you may be able to draw a reasonable conclusion that the patient's current symptoms are related to vestibular decompensation: The patient has recent complaints associated with vestibular dysfunction such as instability or oscillopsia, you find a significant unilateral hypofunction on caloric testing, but the patient can't recall a recent episode of vertigo. In this case, the patient may have suffered a vestibular injury many years ago, compensated adequately without ever knowing the source of the vertigo, then recently experienced a decompensation.
Remember that the things that are used to compensate for a vestibular injury (brain plasticity, vision, tactile feedback and muscle strength) are generally very good when you are young, so compensation is easy. As you age, all those things become compromised, so they do a poorer job of compensating. It is not unusual for a patient to start having symptoms in their 70's when the vestibular injury may have occurred in their 30s.
Decompensation is not related to cerebellar clamp. Cerebellar clamp occurs shortly after (within hours) of an acute unilateral vestibular injury. Cerebellar degeneration, injury or sedation could definitely affect compensation. Also, things like fatigue, stress, anxiety, illness or change in vestibular function can trigger decompensation. When decompensation occurs, the patient would benefit from resuming vestibular rehabilitation exercises, or increasing the frequency and intensity of vestibular exercises being performed for maintaining previously achieved compensation.
In order to evaluate a patient's level of compensation, you must perform direct assessment of VOR function (such as rotational chair, active head rotation or dynamic visual acuity) or measures of functional balance (such as Sensory Organization Testing).
Alan Desmond, Au.D. is the director of Blue Ridge Hearing and Balance Clinic in Bluefield and Princeton, WV, and is the author of Vestibular Function: Clinical and Practice Management, 2nd edition, Thieme, (2011)