title: Hyperventilation-induced nystagmus and vertigo after stereotactic radiotherapy for vestibular schwannoma.
abstract: OBJECTIVE
  To describe the phenomenon of hyperventilation-induced nystagmus (HVN) after stereotactic radiotherapy for vestibular schwannoma.
  
  
  METHODS
  We present 2 patients with vestibular schwannoma and no pretreatment vestibular symptoms who both received stereotactic radiotherapy. Within 2 months of completing treatment, both patients developed intense vertigo while exerting themselves. Video-oculography demonstrated an intense nystagmus with the fast phase directed toward the side of the schwannoma in both patients.
  
  
  METHODS
  Diagnostic.
  
  
  RESULTS
  Patients who have undergone surgical resection of their vestibular schwannoma, or have a large tumor, will often demonstrate HVN with the fast phase directed away from the side of the tumor. This is distinct from patients with smaller lesions who have a fast-phase nystagmus toward the tumor's side. This second type of nystagmus is thought to originate from changes in the extracellular calcium concentration secondary to hyperventilation-induced alkalosis.
  
  
  CONCLUSIONS
  We hypothesize that stereotactic radiotherapy induced greater demyelination of the vestibular nerve leading to the observable sign of HVN. These patients represent the first reported cases of HVN after stereotactic radiation and illustrate the pathophysiology of HVN, which may lead to a greater understanding of the effects of stereotactic radiotherapy.
authors: Department of Otolaryngology-Head and Neck Surgery, Washington University in St. Louis School of Medicine, St. Louis, Missouri 63110 , USA.
authors: Joseph P
authors: JP
authors: Bradley
authors: Timothy E
authors: TE
authors: Hullar
authors: J Gail
authors: JG
authors: Neely
authors: Joel A
authors: JA
authors: Goebel
mesh_terms: D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000209:etiology* / Q000503:physiopathology; D009464:Neuroma, Acoustic / Q000601:surgery*; D009759:Nystagmus, Pathologic / Q000209:etiology* / Q000503:physiopathology; D016634:Radiosurgery / Q000009:adverse effects*; D014717:Vertigo / Q000209:etiology* / Q000503:physiopathology; D014724:Vestibular Function Tests; D014725:Vestibular Nerve / Q000503:physiopathology