Balance Assessment

(Videonystagmography – VNG/ Electronystagmography – ENG)

Description:

The Balance Assessment at Evergreen Speech & Hearing Clinic, Inc. is a protocol that objectively and behaviorally documents vestibular function as well as screens the ocular and somatosensory system’s contribution to balance. The purpose of this test is to determine the location of the disorder (peripheral vs. central), evaluate the patient’s functional abilities, and make appropriate recommendations for the direction of care.

Test time is approximately 75 minutes. For testing validity and patient comfort, the patient is referred to Balance Assessment Patient Instructions located on this website. Additionally, the patient is asked to complete the Balance Assessment Questionnaire, located on this website, prior to testing and bring it to the appointment. The Audiologists at Evergreen Speech & Hearing Clinic are fully certified, have all received post-doctoral and post-graduate training from accredited universities in the administration and interpretation of balance assessments.

The objective assessment of balance is completed utilizing the VNG/ENG protocols in combination with tests of vestibular autorotation, dynamic visual acuity, and sensory organization performance.

Videonystagmography / Electronystagmography (VNG/ENG) During this evaluation, the patient wears a pair of goggles equipped with an infrared camera (VNG) or recording electrodes (ENG) that are connected to a diagnostic computer. The camera/electrodes track eye movement resulting from Vestibular Ocular Reflex (VOR) in response to visual, postural, and temperature varied stimulus. The procedure can be divided into five subcategories: Oculomotor tests, positional and positioning tests, active rotation tests, bithermal caloric tests, and Posturographic tests.

Oculomotor Tests examine the ability to maintain a gaze on distant or moving objects as an indicator of neurological disease. A wide variety of specific eye movements associated with various pathologic conditions are well documented in the literature. Four types of eye movements are of particular interest when we assess balance:

  • Saccades – Rapid eye movements that enable us to redirect our line of site.
  • Pursuit – The ability to follow an object smoothly while maintaining a stable image on the fovea.
  • Optokinetic Nystagmus – Evoked by visually following moving objects in the visual field.
  • Fixation – Eye movements associated with keeping the eyes still.

Positional and Positioning Tests allow the Audiologist to determine if the vestibular system responds normally and symmetrically to changes in head movements. Positional testing detects the presence of nystagmus (tracking eye movements) that may result from being placed in specific head or body positions. The Hallpike Maneuver is a postural (positioning) test that is used in the specific identification of Benign Proximal Positional Vertigo (BPPV), also known as canaloithiasis or cupulolithiasis of the posterior/horizontal semicircular canal. BPPV is the most common cause of dizziness in patients over the age of 50 years, and the most treatable.

Active Head Rotation Tests examine the high frequency vestibular function and efficiency of the horizontal and vertical Vestibular Ocular Reflex.

  • High Frequency testing is designed to evoke nystagmus in patients with asymmetrical vestibular function. The nystagmus is the result of an uneven charging of the velocity storage mechanism. The patient is instructed to shake the head horizontally in a “no” gesture for 20 seconds, after which the recording is made.
  • Vestibular Autorotation Testing (VORTEQ) assesses the horizontal and vertical VOR across a range of frequencies (1-3 Hz). From the relative eye and head velocity data, values for phase, gain, and symmetry are computed and compared to normative data.
  • Dynamic Visual Acuity (DVA) is a threshold of visual resolution achieved during vertical and horizontal head motion (1-3 Hz) compared to static baseline thresholds. This test examines at retinal image stability or the resulting oscillopisia.

Caloric Tests The term caloric indicates a measure of heat transfer. Caloric testing is the warming or cooling of the external auditory canal and temporal bone with air. Changing the temperature of the auditory canal stimulates the horizontal semicircular canal of the irrigated ear, inducing a nystagmus response in the functional ear. By inducing the nystagmus response, the physiologic integrity of the patient’s low frequency right horizontal semicircular canal can be compared to that of the left.

Posturographic Tests examines the patient’s reliance on each of three supporting balance sensory systems: vestibular, vision, and somatosensory. The test provides qualitative information about the patient’s pattern of equilibrium maintenance by systematically causing each of the three sensory inputs to be unreliable. This is accomplished through clinical observation of six conditions: Romberg, Romberg-Vision Deprived, Tandem Romberg, Tandem Romberg – Vision Deprived, Romberg – Somatosensory Deprived, Romberg – Vision and Somatosensory Deprived, Stepping Fukuda.

Indications:

Any patient with acute or chronic dizziness or imbalance for whom acute cardiac and neurological disorders have been ruled out. Additionally, the procedure may be utilized as pre and post intervention as a measure of treatment efficacy.

Significant Findings:

Oculomotor Tests
Spontaneous Nystagmus – The presence of nystagmus in the absence of any known nystagmogenic stimulus. The characteristics of spontaneous nystagmus depend on whether the vestibular problem is peripheral, central, or congenital.

Horizontal and Vertical Gaze – Impaired gaze holding may indicate the presence of a central lesion. Any persistent nystagmus for ocular displacement of 30 degrees or less is considered abnormal. Causes of gaze evoked nystagmus include medication, brainstem or cerebellar disorders, normal variants, ocular muscle fatigue, and congenital nystagmus.

Saccade Tests
Velocity has normal range of 350-750 degrees/second.

Latencies of greater than 400ms. An asymmetry of latency may indicate the presence of a lesion involving the parietal or occipital cortex, however, patient anticipation or lack of cooperation may also influence findings.

Accuracy abnormalities may be subclassified into four groups.

  • Overshoot dysmetria (overshooting target with corrective saccades) with frequency of greater than 50% and amplitudes of greater than 2 degrees are suggestive of cerebellar lesion.
  • Undershoot dysmetria (undershooting target with corrective saccades) that is constant and significant (less than 50% of target displacement) is suggestive of basal ganglia disorder such as Parkinson’s disease.
  • Glissades (gliding to the target) with an obvious pulse step mismatch causes suspicion of brainstem or cerebellar disorder.
  • Pulsion (the pulling of the vertical saccade to the right or left) may be indicative of cerebellar artery infarcts, however, recording of this phenomena is not clinically practical, and therefore not included in this protocol.

Pursuit or Sinusiodal Pendular Tracking is effected by frequency, age, and gender and therefore requires conservative interpretation. Clinically, patients with symmetrical pursuit should be categorized as perfect (gain greater than .8), moderately impaired (gain of .2 to .8), or no pursuit at all (less than .2). No pursuit is suggestive of central vestibular involvement, as is asymmetrical or reversed pursuit.

Optokinetic Tests (OPK) should produce a balanced response to a moving repetitive pattern with gain of .5. Symmetrically reduced gain occurs in visual disorders. Asymmetrical gain can follow complete unilateral peripheral vestibular lesions and briefly following unilateral parietooccipital lesions. Reversed or Inverted OPK occurs in patients with congenital nystagmus.

Positional/Positioning Tests
Positional Nystagmus (not present with head upright, but in one or more position) may be the result of peripheral or central vestibular involvement.

Hallpike Maneuver is used to identify patients with Benign Proximal Positional Vertigo (BPPV). The Classic Hallpike (BPPV response) will show a latency of 1 second or more, duration of less than one minute, present with torsional nystagmus (see video below), may show reversal when patient returns to upright position, and is fatigable (response is less robust with successive trials).

Active Head Rotation Tests
High Frequency Headshake nystagmus of greater than 7 deg/sec is thought to be abnormal, and may be present in patients with a non-compensated vestibulopathy. Nystagmus will beat away from the side of lesion (presenting unilateral weakness) in chronic peripheral vestibular lesions, and toward the site of lesion in acute (first 24 hours) peripheral lesions or with patients with acoustic neuroma.

Vestibular Autorotation results are considered to be normal when Phase values are approximately zero at lower frequencies, and lag at higher frequencies, Gain values approximate .9 at lower frequencies and decline at higher frequencies, and Symmetry values approximate zero at all frequencies. Deviation from the norms in either horizontal or vertical rotation is suggestive of an abnormal Vestibular Ocular Reflex (VOR).

Dynamic Visual Acuity is useful in the identification of horizontal or vertical oscillopsia. Normal patients will demonstrate a decrement of no more than two lines on the visual acuity chart (Micromedical) or 20% (Gans CDVAT).

Caloric Testing
A comparison of the strength of four caloric conditions is made, as is the ability to suppress the response. Cool (24 degree) right ear (RC) and warm (50 degree) left ear (LW) result in left beating nystagmus responses. Cool left (LC), and warm right (RW) result in right beating nystagmus responses.

A determination of Unilateral Weakness or UW (a.k.a. reduced labyrinthine reactivity where one ear’s response is weaker than the other) is made utilizing the following equation:

UW = (LC + LW) – (RC + RW) X 100
(LC + LW + RC + RW)

A determination of Directional Preponderance or DP is made utilizing the equation:

DP = (LC + LW) – (RC + RW) X 100
(LC + LW + RC + RW)

Gans Sensory Organization Performance Test
The Gans SOP Test is best used to look at overall patterns of balance performance through it’s combination of the Romberg, CTSIB and Stepping Fukuda Tests. Although no test of balance function can provide a specific diagnosis, there are well-established patterns of functional impairment that have been found to correlate with various vestibular function tests (Gans Sensory Organization Performance TM – The American Institute of Balance, Seminole FL).

Reporting:

Upon completion of the Balance Assessment, the referring physician will be provided with a detailed report and analysis of the findings.

Suggestions:

To ensure test validity and patient comfort, please refer patient to the Balance Assessment Patient Instructions found in this website.

References:

BALOH, R.W., Dizziness, Hearing Loss, and Tinnitus, FA Davis Co., Philadelphia Wilkins, St. Louis, MO, 2001

CLARK, J.B. “Evaluation of Visual Vestibular Interaction with Dynamic Visual Acuity Test”,Vestibular Update, Issue 20, Micromedical Technologies, 2003

COATS, A., The Audiovestibular System, Chapter Three “Electronystagmography”, Academic Press, Inc. New York, NY, 1975

GOEBEL, J.A., Practical Management of the Dizzy Patient, Lippincott, Williams, and

HALL, J. and MUELLER, G., Audiologist’s Desk Reference, Singular Publishing Group, San Diego, 1997.

JACOBSON, G.P., NEWMAN, C.W., and KARTUSH, J.M., Handbook of Balance Function Testing, Singular Publishing Group, San Diego, CA 1997.

SHEPARD, N.T. and TELIAN, Practical Management of the Balance Disordered Patient, Singular Publishing Group, San Diego.