Foundations

Introduction

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In this module

  1. What CDP is — and what it isn'tFoundation · Trainee · Clinician
  2. Where CDP fits in the vestibular work-upFoundation · Trainee · Clinician
  3. The three protocols at a glanceFoundation · Trainee · Clinician
  4. Historical context: from Nashner to todayTrainee · Clinician
  5. Limits of the techniqueTrainee · Clinician

What CDP is — and what it isn't

Computerised Dynamic Posturography (CDP) is a functional assessment of balance. A patient stands on a force plate inside a movable visual surround while the apparatus systematically degrades each sensory input — vision, somatosensation, and vestibular cues — to reveal how the central nervous system weighs and integrates them.

Unlike calorics or the head impulse test, CDP does not localise a peripheral lesion. It answers a different question: given whatever organic substrate is present, how well can this patient stand? That makes it complementary to, not a replacement for, the rest of the vestibular work-up.

The test takes about 25 minutes in practised hands. It is non-invasive, well tolerated by most patients with a safety harness, and yields three protocols' worth of data — the Sensory Organisation Test (SOT), the Motor Control Test (MCT), and the Adaptation Test (ADT) — each interrogating a different layer of postural control.

Where CDP fits in the vestibular work-up

Think of the vestibular work-up as a stack. At the bottom sit anatomical tests — the head impulse test, calorics, VEMPs — which ask where is the lesion. Above them sit functional tests, of which CDP is the most informative single example. CDP asks how is the patient coping.

This functional layer matters because two patients with identical caloric weaknesses can have very different daily lives. One may have compensated fully and returned to work; the other may still be falling in the dark. CDP can distinguish them when the structural tests cannot.

CDP also plays a role in monitoring. Vestibular rehabilitation typically aims to improve sensory weighting and reduce visual dependence; serial CDP can document that improvement objectively in a way that's hard for symptom diaries alone.

The three protocols at a glance

The Sensory Organisation Test presents six conditions that systematically remove or destabilise visual and somatosensory cues, forcing the patient onto residual inputs — and on conditions 5 and 6, onto vestibular input alone. It is the workhorse of CDP.

The Motor Control Test applies sudden platform translations to evoke automatic postural responses. Its key measurement is the latency of that response, which reflects long-loop brainstem-spinal pathways and is sensitive to central involvement.

The Adaptation Test uses repeated toes-up and toes-down platform rotations. The healthy nervous system rapidly damps the inappropriate sway response across trials — a cerebellum-dependent learning process. Failure of this adaptation is itself a useful finding.

Historical context: from Nashner to today

The technique grew out of the work of Lewis Nashner at Good Samaritan Hospital in Portland through the late 1970s and early 1980s. Nashner's 1982 demonstration that postural sway could be selectively modulated by sway-referencing the surface and surround established the conceptual framework on which all modern CDP rests.

Commercial systems followed in the 1980s and 1990s, with NeuroCom (now Natus Balance Manager) dominating the field. The basic protocol — six SOT conditions, the MCT, and the ADT — has remained remarkably stable, although newer systems add force-plate-based stability tests and adaptive paradigms for rehabilitation use.

Through the 2000s and 2010s, large normative datasets (Ford-Smith 1995, Rine 2018 in paediatrics) refined the age-stratified cutoffs used today, and the Bárány Society consensus criteria for several vestibular disorders began to reference CDP findings as supportive evidence — though never as primary diagnostic criteria.

Limits of the technique

CDP is not a diagnostic test. A normal SOT does not exclude vestibular disease — BPPV in particular is essentially invisible between attacks. An abnormal SOT does not localise the lesion; the same pattern can arise from neuritis, schwannoma, ototoxicity, or a brainstem lacune.

The test is also susceptible to effort, anxiety, and expectation. The aphysiologic patterns described by Cevette and colleagues in 1995 reflect this — a CDP that looks too unusual to be biologically plausible is itself a finding, but a non-specific one.

Finally, CDP requires that the patient can stand for several minutes at a time. Severely deconditioned, frail, or acutely vertiginous patients may not tolerate the protocol. In those cases the rest of the bedside and laboratory work-up has to carry the load.