Understanding the SOM (Sensory Organization Test)

The Sensory Organization Test (SOM) is a cornerstone of moving platform posturography, a quantitative assessment used to evaluate how a patient integrates visual, proprioceptive, and VESTIBULAR cues to maintain balance. Unlike traditional ENG testing (electronystagmography), which primarily assesses the oculomotor and vestibular systems separately, posturography measures functional balance under dynamic conditions. Patients stand on a force plate that can tilt or translate, while visual surroundings are manipulated. Scoring in the SOM provides a objective, composite equilibrium score that reveals deficits across six sensory conditions, from easy (eyes open, fixed support) to challenging (eyes closed, sway-referenced support).

Scoring Metrics and Sensory Analysis

The scoring algorithm in moving platform posturography calculates a VESTIBULAR score by isolating the patient's ability to use inner EAR cues when vision and proprioception are unreliable. This is especially critical when evaluating dizziness of suspected central or peripheral origin. A bilateral vestibular loss will typically produce a characteristic pattern: near-normal scores on conditions with a fixed support surface and visual reference, but sharp drops during conditions 5 and 6 (eyes closed or sway-referenced vision with a sway-referenced platform). Scoring employs peak-to-peak sway amplitude and center-of-pressure measurements, normalized against age-related normative data. Abnormal scores help differentiate between VESTIBULAR, visual, or somatosensory impairments.

Clinical Implications of SOM Patterns in Posturography

Interpreting the SOM profile is essential for targeted rehabilitation. A low VESTIBULAR score (typically below 50% in older adults) suggests poor use of VESTIBULAR input from the inner EAR, often seen in bilateral vestibulopathy or central processing disorders. Combined with patient history, ENG results (e.g., reduced caloric responses), and subjective dizziness scales, posturography enhances diagnostic accuracy. Scoring also tracks recovery: a patient with bilateral vestibular hypofunction may show gradual improvements in composite scores after vestibular rehabilitation. This objective data is invaluable for medicolegal reports, disability determination, and monitoring treatment efficacy in dizziness clinics.

Integrating SOM with Other Vestibular Testing Modalities

While ENG provides insight into the integrity of the peripheral vestibular system (e.g., canal paresis on caloric testing), it does not assess functional balance. Moving platform posturography fills this gap by quantifying how the brain uses VESTIBULAR, visual, and somatosensory signals. The SOM score is calculated automatically by the posturography system, but clinicians must correlate these numbers with the patient's symptoms of dizziness and falls risk. A patient with normal ENG but abnormal SOM may have a central vestibular or multisensory integration deficit. Conversely, a patient with clear bilateral vestibular loss on ENG (e.g., absent responses on both sides) will almost always show severely impaired SOM scores, confirming the functional impact of the inner EAR dysfunction.

In summary, scoring in moving platform posturography—and particularly the SOM sensory analysis—provides a robust, objective measure of VESTIBULAR function in a weight-bearing context. By combining this with patient history, ENG data, and symptom reports, clinicians can accurately diagnose sources of dizziness, identify bilateral impairments, and guide evidence-based therapy. The POSTUROGRAPHY and SOM scores remain essential tools in the modern TESTING battery for balance disorders.