How is the computerized platform posturography test performed in a dizziness evaluation?

Updated: Jun 26, 2018
  • Author: Wayne T Shaia, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

Computerized platform posturography

  • The tests described thus far address only 1 limb of the complex sensory and motor interactions required to maintain balance. Because the maintenance of equilibrium involves contributions from the vestibular system and the visual and somatosensory systems, platform posturography was developed to assess equilibrium as a whole.

  • The most commonly used system is the EquiTest. The patient stands on a platform, is secured in a harness, and faces a visual surround. Under the direction of the computer, the platform and visual surround can move independently or together in response to patient sway. Force plates in the platform monitor the patient's sway and center of gravity. The computer records the information for analysis and uses the information to move the surround during parts of the test.

  • The test protocol comprises 2 parts, namely, the motor-control test and the sensory-organization test. In the motor-control test, the platform administers sudden anteroposterior and posteroanterior translations while the force plates record the patient's response to the perturbations. Three movements (small, medium, and large) are used to cause specified rotations around the ankle joint, shifting the center of gravity.

  • In a different motor-control test, small toes-up and toes-down platform rotations are presented. During both movements, the force plates record the distribution of weight over the feet during the movement, and the latency of the patient response to platform movement is calculated. Conditions that disturb spinal reflexes increase response latency during the motor control test. Adaptation to repeated movements is also calculated.

  • In the sensory-organization test, the platform and visual surround are manipulated to test the patient's relative reliance on VOR, visual, and proprioceptive/somatosensory systems. During the first 3 test conditions, the platform remains fixed. In the first test condition, the subject stands quietly with eyes open while the platform and visual surround remain stationary. In the second test condition, the patient stands with eyes closed. In the third condition, the visual surround moves in response to information from the force plate, ie, when the patient leans forward, the visual surround falls away from the patient proportionally (sway referencing). The effect of this condition is to remove reliable visual cues, forcing the use of the vestibular system and, more importantly, the somatosensory system.

  • In test conditions 4, 5, and 6, the platform moves to follow the forward-backward sway of the patient. Platform movement removes reliable somatosensory cues for equilibrium. In condition 4, the visual surround remains fixed while the subject's eyes are open. In condition 5, the patient's eyes are closed. In condition 6, both the platform and visual surround are sway referenced, providing inaccurate visual and somatosensory information and forcing the reliance on vestibular inputs.

  • The clinical usefulness of platform posturography continues to be debated. In general, the consensus is that the test is not diagnostic for specific disease entities. The actual usefulness of the test is in the functional evaluation of equilibrium in the following situations:

    • Responses are documented in subjects with suspected malingering or psychiatric disorders. The ability of platform posturography to detect malingerers by their specific patterns of response is well established.

    • A program of vestibular rehabilitation is planned, and response to treatment is monitored in patients who have a variety of equilibrium problems. Patients who may be at particular risk of falling and sustaining possible injury can be monitored.

    • Patients who have disequilibrium because of elevated cerebrospinal fluid pressure can be monitored.


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