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VNG (Videonystagmography) Analysis Report

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SECTION 1 - SACCADE TESTING

Horizontal Saccades

• At 0.45 Hz, a significant left eye velocity drop (164.45 vs 322.85 °/s) is noted - this asymmetry is abnormal and may reflect a right-beating preference or left-sided oculomotor pathway dysfunction
• Precision at 0.45 Hz drops markedly in both eyes (30.33/30.44), suggesting dysmetric saccades at this frequency
• The Random Frequency + Amplitude task shows precision exceeding 100 (103-104%), which is above normal; this can indicate saccadic overshoot (hypermetria) - a cerebellar sign
• Latencies are mildly prolonged at some frequencies (280-295 ms at random frequency; normal is typically <200-250 ms for age 74, but borderline)

Vertical Saccades

• Dramatically elevated left eye vertical saccade velocities (708-1313 °/s) compared to the right eye (129-402 °/s) - this represents a striking interocular velocity asymmetry
• Extreme precision values for left eye (162-219%) strongly indicate saccadic dysmetria / hypermetria of the left eye in vertical plane
• Left eye velocities of >700 °/s and reaching 1313 °/s in the random frequency condition are far outside normal ranges (normal peak vertical saccade velocity ~300-500 °/s)
• Left eye vertical upward velocity (1054.95 °/s) and downward velocity (950.61 °/s) in hemifield testing confirm this finding is directionally non-selective
• This pattern of one eye showing dramatically different metrics than the other in vertical saccades is a strong indicator of a central oculomotor pathway lesion, specifically the midbrain internuclear ophthalmoplegia (INO) pathway or cerebellar/brainstem pathology

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SECTION 2 - SMOOTH PURSUIT TESTING

• There is a consistent and profound deficit in left eye smooth pursuit across all test conditions and directions - gains of 0.05-0.14 in many conditions
• The right eye shows milder pursuit degradation, worse in the vertical plane (0.21-0.25 upward) and at higher frequencies
• Severely reduced upward vertical smooth pursuit in the right eye (0.21) may indicate upgaze pursuit pathway impairment (dorsal midbrain or cerebellar vermis)
• The profound left eye smooth pursuit deficit combined with abnormal saccades points to a left-sided central oculomotor pathway lesion

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SECTION 3 - OPTOKINETIC (OKN) TESTING

• Horizontal OKN (10°) is symmetric and normal bilaterally - a reassuring finding
• Reduced bottom-to-top OKN (0.65 both eyes) suggests impairment of upward optokinetic response - consistent with the vertical pursuit impairment
• Absent/uncalculable vertical OKN at 20° may reflect dorsal midbrain or cerebellar pathway dysfunction
• The fast phase direction appearing at 18-27° in left-to-right 20° OKN is an unusual finding potentially suggesting intrusion nystagmus at larger amplitudes

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SECTION 4 - SPONTANEOUS NYSTAGMUS

• No spontaneous nystagmus in light or dark - argues against active acute peripheral vestibular lesion (e.g., no Spontaneous nystagmus = compensated or central)
• Post-head-shake nystagmus (HSN): SPV -5.72 °/s right, -3.86 °/s left. Mild negative values suggest a left-beating direction after head shake, pointing to a right-side weaker vestibular response (stimulation of the stronger left system rebounds). Requires caloric correlation.
• Hyperventilation-induced vertical nystagmus (SPV -4.86 °/s, amplitude 2.08°, frequency 0.87 Hz) in the right eye only is a red flag finding - hyperventilation-induced nystagmus can occur in demyelinating lesions (MS), vestibular schwannoma, or perilymphatic fistula

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SECTION 5 - GAZE TESTING

• Gaze-evoked nystagmus appearing only without fixation and specifically in upgaze (vertical nystagmus bilaterally when looking up without fixation) is a central sign, associated with cerebellar or dorsal midbrain pathology
• Left eye SPV of 6.38 °/s in upgaze without fixation is notably higher than the right (1.87 °/s) - consistent with the left eye oculomotor deficit theme throughout this report
• All gaze positions with fixation are normal - fixation suppresses the nystagmus (distinguishing it from a fixation-failure central lesion; the fixation system is intact)

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SECTION 6 - POSITIONAL TESTING (DIX-HALLPIKE)

• Bilateral positive Dix-Hallpike responses - nystagmus present in BOTH right and left Dix-Hallpike supine positions
• Only the left eye records nystagmus; the right eye shows nothing in both positions - this is an important asymmetry
• Nystagmus frequency of ~1.02-1.21 Hz is typical for BPPV
• However, truly classical posterior canal BPPV would typically be unilateral and show characteristic upbeat-torsional nystagmus. Bilateral positional nystagmus in both Dix-Hallpike positions, combined with central oculomotor findings, raises consideration of central positional nystagmus vs bilateral BPPV

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SECTION 7 - McCLURE-PAGNINI (HORIZONTAL CANAL BPPV TEST)

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SECTION 8 - SUBJECTIVE VISUAL VERTICAL (SVV)

• Both the clockwise (+6°) and anti-clockwise (-10°) conditions are significantly abnormal, showing large deviations in opposite directions
• This large variability between conditions (6° right vs 10° left) suggests either poor cooperation, severe ocular tilt reaction, or central otolith pathway dysfunction
• A blank background deviation of -2° is borderline normal, suggesting some preserved otolith function
• SVV abnormality is associated with lesions affecting the utricular-ocular motor pathway - including brainstem (lateral medullary), cerebellar, and thalamic lesions

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INTEGRATED DIAGNOSTIC SUMMARY

Test-by-Test Abnormality Matrix

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POSSIBLE DIAGNOSES

Primary Diagnosis (Most Likely)

Central Component - High Priority

• Profound smooth pursuit deficits (especially vertical and left eye)
• Saccadic hypermetria (precision >100-200%)
• Dramatically elevated vertical saccade velocities in the left eye
• Vertical gaze-evoked nystagmus without fixation
• Abnormal SVV with large inter-condition variability
• Possible differentials: cerebellar degeneration (spinocerebellar ataxia), posterior fossa lesion (tumor, infarct), multiple sclerosis, or Wernicke's encephalopathy

• The profound and consistent left eye deficit in saccade velocity and smooth pursuit across all axes, while right eye is relatively spared, is highly suggestive of a left-sided INO
• INO is caused by a lesion in the medial longitudinal fasciculus (MLF) and can result from demyelination (MS), brainstem infarct, or tumor
• In a 74-year-old male, cerebrovascular INO (small vessel disease / lacunar infarct of the MLF) is the most likely etiology

• Severely reduced upward vertical pursuit (right eye 0.21, left eye 0.05)
• Reduced upward OKN (bottom-to-top)
• Vertical gaze nystagmus on upgaze
• These suggest dorsal midbrain or pretectal pathology

Peripheral Component

• Positive Dix-Hallpike both sides
• Nystagmus frequency ~1 Hz in positional testing
• Caveat: The predominantly left-eye-only nystagmus recording and bilateral positivity also raises possibility of central positional nystagmus - further evaluation (MRI) is essential to differentiate

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CLINICAL RECOMMENDATIONS

1. Urgent MRI Brain with brainstem and posterior fossa sequences (with gadolinium) - to evaluate for:
   • MLF lesion (lacunar infarct, MS plaque) causing INO
   • Dorsal midbrain or pretectal lesion
   • Cerebellar pathology (atrophy, infarct, tumor)
   • Posterior fossa mass
2. Neurology consultation (urgent) - given the strong central oculomotor signs in a 74-year-old male, stroke/TIA must be actively ruled out
3. Cardiovascular workup - cerebrovascular risk assessment (BP, lipids, HbA1c, carotid Doppler, cardiac echo if indicated)
4. Ophthalmology/Neuro-ophthalmology evaluation - to clinically confirm INO, assess for nystagmus characteristics (particularly in upgaze), and evaluate the SVV findings formally
5. Canalith Repositioning (Epley Maneuver) - may be attempted for the positional component (bilateral BPPV), but should only be done after central pathology has been ruled out by MRI
6. Caloric testing - notably absent from this report; this is a standard component of a complete VNG battery. Adding bithermal caloric testing would help quantify unilateral vestibular weakness and directional preponderance.
7. VEMP testing (cVEMP and oVEMP) - to evaluate saccule, utricle, and their central projections; would help localize the otolith pathway lesion indicated by the SVV abnormality

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SUMMARY IMPRESSION

• Left eye-predominant saccade and smooth pursuit deficits consistent with a left MLF lesion (INO)
• Vertical gaze/pursuit impairment pointing to dorsal midbrain or cerebellar involvement
• Hyperventilation-induced nystagmus (red flag for demyelination or retrocochlear pathology)
• Abnormal SVV suggesting otolith pathway disruption

⚠️ Clinical Disclaimer: This analysis is based solely on the numerical and descriptive data extracted from the VNG report. A definitive diagnosis requires clinical correlation, neurological examination, and neuroimaging. The treating physician should integrate these findings with the patient's full history, symptoms, and examination findings.