Disease Patterns

Aphysiologic Patterns

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Signature on CDP

The figure below shows the archetypal Aphysiologic pattern across the six SOT conditions, MCT response, and ADT adaptation, compared against an age-matched normal reference.

SOT pattern vs normal

MCT — medium-amplitude backward translation

ADT — sway energy across five trials per direction

Teaching point. The Cevette (1995) hallmark: paradoxically worse performance on easy conditions (C1–C4) than on the harder C5/C6. Combined with high intertrial variability, this pattern raises the question of functional dizziness or feigned disease — but is non-specific and must be interpreted alongside the full clinical picture.

In this module

Aphysiologic patterns — definitionsFoundation · Trainee · Clinician
Cevette criteriaTrainee · Clinician
Differential considerationsTrainee · Clinician
Medico-legal contextClinician

Aphysiologic patterns — definitions

Aphysiologic patterns on CDP are configurations that don't fit any physiologically-plausible disease. The classic example is the Cevette inversion: condition 5 and 6 (the hardest, vestibular-only conditions) paradoxically better than condition 1 or 2 (the easiest). No real disease produces this.

Aphysiologic patterns are non-specific. They can occur in functional dizziness, deliberate effort modulation (malingering), severe anxiety, and occasionally in genuinely organic disease where extreme trial-to-trial variability produces atypical means. The pattern itself is a finding; the interpretation requires clinical context.

Reporting an aphysiologic pattern is appropriate when the configuration is clearly non-physiological. Naming it 'malingering' on the basis of CDP alone is not — many other causes can produce the same picture, and CDP is a poor lie-detector.

Cevette criteria

Cevette and colleagues (1995) defined a set of criteria for identifying aphysiologic CDP patterns. The criteria use multiple discordances: C5 better than C1, C5 better than C2, exaggerated inter-trial variability (typically more than 25 EQS points within a condition), and combinations of these.

The original criteria were derived in a sample including known feigners, validating against group-level discrimination. They have been used clinically since but have known false-positive rates in patients with severe anxiety and in some organic pathologies producing extreme variability.

A reasonable clinical threshold is: a single inversion (C5 > C1, for example) by more than 10 EQS points raises the question of aphysiologic pattern; multiple inversions or large inter-trial variability across multiple conditions strengthens the conclusion. Borderline configurations should be reported with appropriate uncertainty rather than over-called.

Differential considerations

The differential for an aphysiologic CDP pattern includes:

Functional dizziness without intent to deceive — PPPD overlay, somatoform variants, and post-traumatic functional disorders can produce aphysiologic patterns through inconsistent effort or attention.

Severe anxiety — extreme anxiety during testing can produce trial-to-trial variability large enough to mimic aphysiologic patterns. Re-testing on a separate occasion in a calmer state can clarify.

Deliberate effort modulation — patients with secondary gain (litigation, disability claims) may modulate effort. The CDP cannot reliably distinguish this from genuine functional disorder.

Organic disease with extreme variability — rare, but possible in severe cerebellar disease, fluctuating Ménière's, and some demyelinating presentations. Cross-correlation with the other CDP protocols and the clinical picture is essential.

Medico-legal context

Aphysiologic CDP findings frequently surface in medico-legal contexts: personal-injury claims, disability evaluations, fitness-for-duty assessments. The temptation to use the finding as direct evidence of malingering should be resisted.

Appropriate medico-legal language describes what the CDP showed (an aphysiologic configuration meeting Cevette criteria), notes the differential (functional disorder, anxiety, effort modulation, atypical organic disease), and defers attribution to the multidisciplinary assessment. CDP is rarely the right test on which to base a definitive opinion about deception.

Where multiple tests across the work-up show consistent aphysiologic or non-organic patterns — for example, an aphysiologic CDP plus inconsistent posturography on different days plus give-way weakness on neurological exam plus a normal MRI — the cumulative weight may support a functional or feigned conclusion. Even then, the attribution belongs to the clinician integrating everything, not to the CDP report.