Disease Patterns
Bilateral & Unilateral Vestibular Loss
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Signature on CDP
The figure below shows the archetypal Vestibular pattern pattern across the six SOT conditions, MCT response, and ADT adaptation, compared against an age-matched normal reference.
In this module
- Bilateral and unilateral loss — overviewFoundation · Trainee · Clinician
- Unilateral peripheral lossFoundation · Trainee · Clinician
- Bilateral vestibulopathyTrainee · Clinician
- Central compensation and recoveryTrainee · Clinician
Bilateral and unilateral loss — overview
Vestibular loss can be unilateral or bilateral, partial or complete, acute or chronic. The CDP pattern depends on all four axes. Acute losses produce dramatic patterns; chronic compensated losses can look near-normal. Bilateral losses produce more severe and stereotyped patterns than unilateral losses.
CDP is sensitive to severity but not to side. A unilateral loss does not produce a directionally-asymmetric SOT — body sway is roughly symmetric in either direction on every condition, because postural control draws on bilateral vestibular input integrated centrally.
What CDP does well in this group: confirms that a structural lesion has functional consequences, monitors compensation over time, and identifies the rare patient whose CDP pattern is much worse than their imaging would suggest (raising the question of additional central involvement).
Unilateral peripheral loss
Acute unilateral vestibular loss — neuritis, labyrinthitis, the early hours after labyrinthectomy — produces the classical vestibular pattern: selective reduction on C5 and C6, falls common on C5, with C1–C4 typically intact. About 70% of acute neuritis patients show this pattern (Park 2017).
Chronic compensated unilateral loss is much milder. Most patients with caloric weaknesses of 30–50% have entirely normal CDPs once central compensation has occurred, usually within three to six months. A patient with documented unilateral weakness but persistently abnormal CDP at six months has either failed to compensate, has an additional problem, or has developed a secondary disorder like PPPD.
The asymmetry of caloric findings does not need to predict the asymmetry of CDP findings, because the CDP test does not isolate one side. A 70% unilateral weakness can produce a normal CDP if compensation is good, and a 20% weakness can produce an abnormal CDP if compensation has failed.
Bilateral vestibulopathy
Bilateral vestibulopathy produces the most severe and stereotyped CDP pattern in the disorder library. C5 and C6 are essentially zero — the patient cannot stand on a sway-referenced surface without vestibular input. C4 is often reduced too; even C2 can be borderline in severe cases.
The Bárány Society 2017 criteria for bilateral vestibulopathy require bedside HIT abnormality bilaterally plus reduced caloric responses bilaterally (sum of maximum slow-phase velocities < 6°/s per side). CDP supports the diagnosis but is not part of the criteria.
Aminoglycoside ototoxicity is the most common identifiable cause. Other causes include autoimmune inner-ear disease, recurrent Ménière's affecting both labyrinths, and idiopathic progressive vestibulopathy. CDP can document the severity baseline and track rehabilitation response.
Central compensation and recovery
Central compensation after unilateral vestibular loss occurs through several mechanisms: rebalancing of resting vestibular tone between the two vestibular nuclei, re-weighting of sensory inputs toward intact vision and somatosensation, and learning of new motor patterns through cerebellar plasticity.
The time course is variable. Most patients show substantial CDP improvement within four to six weeks of an acute lesion, and reach a plateau by three to six months. A patient still showing a severe vestibular pattern at six months is unusual and warrants a careful look at compliance with vestibular rehabilitation, central involvement, and PPPD overlay.
Vestibular rehabilitation appears to accelerate compensation. Serial CDP can document this objectively — a patient whose composite rises from 50 to 70 over eight weeks of therapy has measurably improved, regardless of whether their symptoms have resolved completely.