Vibration and Hyperventilation-induced Nystagmus from Vestibular Schwannoma

𝗢𝗿𝗶𝗴𝗶𝗻𝗮𝗹 𝗗𝗲𝘀𝗰𝗿𝗶𝗽𝘁𝗶𝗼𝗻: This is a 50-yo-woman with imbalance, and with fixation removed on her examination (with Frenzel goggles), there was no spontaneous nystagmus. Using a handheld vibrator to vibrate the mastoids and vertex, there was a rightward slow phase and corrective leftward fast phase (left-beating nystagmus). Vibration is an excitatory vestibular stimulus, and when vestibular asymmetry is present, vibration can transiently exacerbate this asymmetry and generate a slow phase that is ipsilateral to the pathology/vestibular hypofunction (towards the right in this case). After hyperventilating the patient for 40 seconds, there was robust right-beating and torsional (towards right ear) nystagmus. Hyperventilation transiently alters neuronal conductivity across a demyelinated segment of the 8th cranial nerve (e.g., acoustic neuroma or neurovascular compression), and can generate excitatory>inhibitory pattern of nystagmus (excitatory in this case with contralesional, leftward slow phase, and ipsilesional, rightward fast phases). MRI demonstrated a right sided vestibular schwannoma which explained both the right hypofunction (LBN with vibration), and the excitatory pattern (RBN) of her hyperventilation-induced nystagmus. 𝗡𝗲𝘂𝗿𝗼-𝗼𝗽𝗵𝘁𝗵𝗮𝗹𝗺𝗼𝗹𝗼𝗴𝘆 𝗮𝗻𝗱 𝗡𝗲𝘂𝗿𝗼-𝗼𝘁𝗼𝗹𝗼𝗴𝘆 𝗧𝗲𝘅𝘁𝗯𝗼𝗼𝗸 𝗟𝗲𝗴𝗲𝗻𝗱: This patient presented with imbalance, and with fixation removed on her examination (with Frenzel goggles), there was no spontaneous nystagmus. Using a handheld vibrator to vibrate the mastoids and vertex, there was a rightward slow phase and corrective leftward fast phase (left-beating nystagmus). Vibration is an excitatory vestibular stimulus, and when vestibular asymmetry is present, vibration can transiently exacerbate this asymmetry and generate a slow phase that is ipsilateral to the pathology/vestibular hypofunction (toward the right in this case). After hyperventilating the patient for 40 seconds, there was robust right-beating and torsional (toward right ear) nystagmus. Hyperventilation transiently alters neuronal conductivity across a demyelinated segment of the eighth cranial nerve (e.g., acoustic neuroma or neurovascular compression), and can generate excitatory> inhibitory pattern of nystagmus (excitatory in this case with contralesional, leftward slow phase, and ipsilesional, rightward fast phases). MRI demonstrated a right-sided vestibular schwannoma which explained both the right hypofunction (LBN with vibration), and the excitatory pattern (RBN) of her hyperventilationinduced nystagmus https://collections.lib.utah.edu/details?id=1213447