title: Head impulse gain and saccade analysis in pontine-cerebellar stroke and vestibular neuritis.
abstract: OBJECTIVE
  We sought to quantify and compare angular vestibulo-ocular reflex (aVOR) gain and compensatory saccade properties elicited by the head impulse test (HIT) in pontine-cerebellar stroke (PCS) and vestibular neuritis (VN).
  
  
  METHODS
  Horizontal HIT was recorded ≤7 days from vertigo onset with dual-search coils in 33 PCS involving the anterior inferior, posterior inferior, and superior cerebellar arteries (13 AICA, 17 PICA, 3 SCA) confirmed by MRI and 20 VN. We determined the aVOR gain and asymmetry, and compensatory overt saccade properties including amplitude asymmetry and cumulative amplitude (ipsilesional trials [I]; contralesional trials [C]).
  
  
  RESULTS
  The aVOR gain (normal: 0.96; asymmetry = 2%) was bilaterally reduced, greater in AICA (I = 0.39, C = 0.57; asymmetry = 20%) than in PICA/SCA strokes (I = 0.75, C = 0.74; asymmetry = 7%), in contrast to the unilateral deficit in VN (I = 0.22, C = 0.76; asymmetry = 54%). Cumulative amplitude (normal: 1.1°) was smaller in AICA (I = 4.2°, C = 3.0°) and PICA/SCA strokes (I = 2.1°, C = 3.0°) compared with VN (I = 8.5°, C = 1.3°). Amplitude asymmetry in AICA and PICA/SCA strokes was comparable, but favored the contralesional side in PICA/SCA strokes and the ipsilesional side in VN. Saccade asymmetry <61% was found in 97% of PCS and none of VN. Gain asymmetry <40% was found in 94% of PCS and 10% of VN.
  
  
  CONCLUSIONS
  HIT gains and compensatory saccades differ between PCS and VN. VN was characterized by unilateral gain deficits with asymmetric large saccades, AICA stroke by more symmetric bilateral gain reduction with smaller saccades, and PICA stroke by contralesional gain bias with the smallest saccades. Saccade and gain asymmetry should be investigated further in future diagnostic accuracy studies.
  
  
  METHODS
  This study provides Class II evidence that aVOR testing accurately distinguishes patients with PCS from VN (sensitivity 94%-97%, specificity 90%-100%).
authors.affiliation: From the Central Clinical School (L.C., G.M.H., S.A.), Faculty of Medicine, University of Sydney; and Institute of Clinical Neurosciences (L.C., M.T., G.M.H., S.A.), Royal Prince Alfred Hospital, Sydney, Australia. lukec@icn.usyd.edu.au.
authors.forename: Luke
authors.initials: L
authors.lastname: Chen
authors.affiliation: From the Central Clinical School (L.C., G.M.H., S.A.), Faculty of Medicine, University of Sydney; and Institute of Clinical Neurosciences (L.C., M.T., G.M.H., S.A.), Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Todd
authors.affiliation: From the Central Clinical School (L.C., G.M.H., S.A.), Faculty of Medicine, University of Sydney; and Institute of Clinical Neurosciences (L.C., M.T., G.M.H., S.A.), Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Gabor M
authors.initials: GM
authors.lastname: Halmagyi
authors.affiliation: From the Central Clinical School (L.C., G.M.H., S.A.), Faculty of Medicine, University of Sydney; and Institute of Clinical Neurosciences (L.C., M.T., G.M.H., S.A.), Royal Prince Alfred Hospital, Sydney, Australia.
authors.forename: Swee
authors.initials: S
authors.lastname: Aw
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002531:Cerebellum / Q000473:pathology*; D005260:Female; D064087:Head Impulse Test; D019416:Head Movements; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011149:Pons / Q000473:pathology*; D011446:Prospective Studies; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D012438:Saccades / Q000502:physiology*; D020521:Stroke / Q000473:pathology* / Q000503:physiopathology; D020338:Vestibular Neuronitis / Q000503:physiopathology*; D055815:Young Adult