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Vestibular Neuritis

Vestibular Neuritis: Pathogenesis and Clinical Findings Authors: Ryan Chan Jonathan Wong Reviewers: Mehul Gupta Davis Maclean Saud Sunba Yan Yu* Euna Hwang* * MD at time of publication Recent viral illness or upper respiratory tract infection Virus spreads along upper respiratory mucosa and into the inner ear structures Vestibular Neuritis Presumed idiopathic viral-induced inflammation of the vestibular nerve; typically unilateral Reactivation of Herpes Simplex Virus-1 in vestibular (Scarpa’s) ganglion Inflammatory cell infiltration leads to degeneration and atrophy of the vestibular nerve Superior Vestibular Neuritis (40-48%) Inflammatory cells traverse through only one long bony canal, easier for inflammatory cell infiltration Loss of afferent innervation from the superior and horizontal semicircular canal (SCC), utricle, and parts of the saccule Combined Superior Vestibular Neuritis and Inferior Vestibular Neuritis (34-56%) Inferior Vestibular Neuritis (1.3-18%) Inflammatory cells must pass through two separate bony canals, making inflammatory cell infiltration more difficult Loss of afferent innervation from the posterior semicircular canal (SCC) and saccule Utricular degeneration Displacement of otoliths/ otoconia (commonly into the posterior SCC) BPPV (can occur several months after onset of neuritis) Loss of horizontal SCC afferent neuron signaling to the brain Unilateral Loss or ↓ of normal nystagmus response to Caloric Testing (insertion of cold and warm water/air into the ear canal while supine) Loss of utricular afferent neuron signaling to the brain ↓ or absent Ocular Vestibular- Evoked Myogenic Potentials (VEMPs) and Normal Cervical VEMPs ↓ unilateral vestibular input to the brain leads to acute phase symptoms (over time, brain can compensate which allows for some symptom improvement) Loss of posterior SCC and saccular afferent neuron signaling to the brain ↓ or absent Cervical VEMPs, but Ocular VEMPs are normal ↓ or absent input to the ipsilateral vestibular nuclei elicits a vestibular nucleus response similar to contralateral SCC excitation Acute-Phase Spontaneous Nystagmus Fast phase beats away from the affected side (3- 10 days) And Loss of ocular fixation on Head Impulse Test ↓ or absent saccular input to the lateral vestibular nuclei (e.g., lateral vestibulospinal tract) results in the loss of lower limb postural adjustability Postural Instability (e.g., abnormal Romberg/sharpened Romberg, Fukuda step test) Bilateral mismatch of vestibular information to the brain Peripheral Vertigo (lasts several hours to days; rapid onset, severe, constant) Nausea and Vomiting Only the vestibular part of the vestibulo- cochlear nerve is affected, not the cochlear nerve No Hearing Loss or Tinnitus Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published October 19, 2021 on www.thecalgaryguide.com