Clinical Medicine and the Nervous System Consulting Editor: Michael Swash

Syndromes that have an underlying neurological basis are common prob­lems in many different specialties. Clinical Medicine and the Nervous System is a series of monographs concerned with the diagnosis and man­agement of clinical problems due primarily to neurological disease, or to a neurological complication of another disorder. Thus the series is par­ticularly concerned with those neurological syndromes that may present in different contexts, often to specialists without special expertise in neurology. Since the range of clinical practice embraced by neurologists is wide, the books in this series will appeal to many different specialists in addition to neurologists and neurosurgeons. It is the aim of the series to produce individual volumes that are succinct, informative and complete in themselves, and that provide sufficient practical discussion of the issues to prove useful in the diagnosis, investigation and management of patients. Important advances in basic mechanisms of disease are em­phasized as they are relevant to clinical practice. In particular, individual volumes in the series will be useful especially to neurologists, neuro­surgeons, physicians in internal medicine, oncologists, paediatricians, neuro-radiologists, rehabilitationists, otorhinolaryngologists and oph­thalmologists, and to those in training in these specialties.

Titles in the series already puhlished:

Headache Richard Peatfield

Epilepsy: Electroclinical Syndromes Edited by Hans Liiders and Ronald P. Lesser

The Heart and Stroke Edited by Anthony J. Furlan

Hierarchies in Neurology Christopher Kennard and Michael Swash

Imaging of the Nervous System Edited by Paul Bulter

Michael Swash, MD, FRCP, MRCPath The Royal London Hospital

Forthcoming titles in the series:

Malignant Brain Tumours Edited by David G.T. Thomas and 0.1. Graham

Diseases of the Spinal Chord Edited by E.M. Critchley and A. Eisen

Motor Neuron Disease Edited by Nigel Leigh and Michael Swash

Electrophysiological Diagnosis E.M. Sedgwick

Hydrocep: .tlS and the Cerehrospinal .'Iuid Edited by J.D. Pickard

Vertigo: Its Multisensory Syndromes

Thomas Brandt

With 88 Figures

Springer-Verlag London Berlin Heidelberg N ew York Paris Tokyo Hong Kong

Thomas Brandt, Professor of Neurology, Director Neurologische Klinik, Ludwig-Maximilians-U niversitiit Munchen, Klinikum Grosshadern, Marchioninistrasse 15, SOOO Munchen 70, Germany

Cons lilting Editor

Michael Swash, MD, FRCP, MRCPath, Consultant Neurologist, Neurology Department, The Royal London Hospital, Whitechapel, London EI IBB, UK

The illustration on the cover, drawn by the author, represents the lahyrinth with the hrainstem and cerebellum in the hackground.

ISBN-13: 978-1-4471-3344-5 e-ISBN-13: 978-1-4471-3342-1 DOl: 10.1007/978-1-4471-3342-1

British Lihrary Cataloguing in Publication Data Brandt, Thomas Vertigo: its multisensory syndromes I. Man. Vertigo I. Title II. Series 616.R41 ISBN-13: 978-1-4471-3344-5

Library of Congress Cataloging-in-Puhlication Data Brandt. Thomas, 1943-Vertigo: its multisensory syndromes/Thomas Brandt p. cm - Clinical medicine and the nervous system) Includes hibliographical references and index. ISBN-13: 978-1-4471-3344-5 I. Vertigo. I. Title. II. Series. RBlS0.V4B73 1991 616.R'41-dc20 90-41R63

CIP

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© Springer-Verlag London Limited 1991 Softcover reprint of the hardcover 15t edition 1991

The use of registered names, trademarks etc. in this puhlication docs not imply, even in the ahsence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore free for general use.

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Consulting Editor's Foreword

Dizziness disequilibrium, loss of balance and falling are common complaints that are sometimes associated with serious disease, yet may also be due to benign disturbances of the complex systems of receptor organs, and neural pathways, that determine the normal appreciation of the body's position in space, the velocity of any displacement, and the compensatory mechanisms necessary to retain equilibtium with the internal and external forces operating on the body. These complex mechanisms have been understood in increasing detail in recent years, and the disturbances of function that lead to clinical problems have become more accessible to clinical investigation and measurement. Just as the symptom of vertigo itself may result from multisensory disturbances, so the clinical disorders that produce this group of symptoms may themselves result from disorders that fall within the provinces of otorhinolaryngology, neurology, psychiatry, neurosurgery and neuroophthalmology. Modern methods of clinical investigation in these areas overlap to some extent, but are often highly specialised and even inaccessible to the clinician in another specialty.

In this book Thomas Brandt has brought his unique experience to bear on this complex but fascinating area of medical practice, and has shown how appropriate and complete investigation can unravel the nature of the underlying disorder, and result in adequate and effective treatment of many of these problems. Modern techniques of electrophysiological investigation of clinical measurement of the physiological disorder, and of imaging the middle and inner ear and the posterior fossa, all contribute to the management of patients with vertigo. Professor Brandt's experience of patients with this clinical symptom is unrivalled, and all those called upon to manage such patients will benefit from study of the methods of assessment and treatment he advocates.

VI Consulting Editor's Foreword

His approach - that vertigo results from disturbance in the function of one or more sensory inputs to the nervous system -provides the apt title for the book.

Michael Swash, MD, FRCP, MRCPath

The Royal London Hospital, London August 1990

Preface

Vertigo consists of a variety of syndromes which are surprisingly easy to diagnose and can, in most cases, be treated effectively. However treatment requires an interdisciplinary approach to the patient which is unusual for clinicians who have usually been trained to specialise in a particular area. Sensorimotor physiology is the key to an understanding of the pathogenesis of vertigo; careful history-taking and otoneurological examination are the key to diagnosis.

The book is organised in sections covering the major sub­divisions of vertigo, including peripheral labyrinthine disorders (Meniere's disease, vestibular neuritis, perilymph fistulas), central vestibular disorders (vestibular epilepsy, downbeat/upbeat nystagmus), positional, vascular, traumatic and familial vertigo, vertigo in childhood and vertigo related to drugs. Sections are further subdivided into chapters covering particular aspects, for example the chapter on migraine and vertigo in the section on vascular vertigo. There is a full description of the clinical features and diagnostic procedures for each disease (with summarising tables), and special emphasis is placed on the relationship between management and the underlying pathological mechanisms.

Most diseases are referred to in several different sections in order to facilitate the differential diagnosis of conditions with similar signs and symptoms. The section on vertigo arising from multisensory interaction covers non-vestibular syndromes such as visual vertigo and cervical vertigo and, more importantly, the psychogenic vertigo syndromes; the latter are the third commonest cause of vertigo in patients seen by neurologists.

This book will contribute to an improvement in diagnosis and management in patients suffering from vertigo and disequilibrium. A further demanding goal of this book is to establish a platform

viii Preface

from which physiologists and clinicians may launch cooperative research concerning the intriguing mechanisms of spatial orient­ation, oculomotor and postural control and ultimately to aid patients with vertigo.

Acknowledgements

I wish, in particular, to record my appreciation for the help I re­ceived from Malcolm Hawken who read the manuscript in its entirety. His critical comments considerably improved earlier drafts. My thanks are also due to Marianne Dieterich who con­tributed particularly to the tables and diagrams based on her clinical experience in differential diagnosis of vertigo syndromes.

I am indebted to Ursula Turbanisch and Beatrix Pfreundner for excellent secretarial help and to Vida Holtzman for preparing many of the diagrams. Pam Decker carefully read some chapters. Finally I would also like to thank Michael Swash, Michael Jackson and Wendy Darke from Springer Verlag for their helpful com­ments during the preparation of the book.

Miinchen Jan uary 1990 Thomas Brandt

Contents

Glossary ............................................ XVll

1 Introduction...................................... 1 The Vertigo Syndromes ............................... 1

Signs and Symptoms ................................ 2 The Mismatch Concept ............................. 3

The Vestibulo-ocular Reflex (VOR) .................... 4 VOR Mediation of Perception and Postural Adjustments 5

Vestibulospinal Reflexes .............................. 7 Approaching the Patient .............................. 9 Medical and Physical Therapy . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Vestibular Compensation ........................... 16 Vestibular Exercises and Physical Therapy of Ataxias . . . . 17

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Section A VESTIBULAR NERVE AND LABYRINTHINE DISORDERS 25

2 Vestibular Neuritis .............. _ . . . . . . . . . . . . . . . . . 29 The Clinical Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Aetiology and Site of the Lesion ...................... 34 Management ...................................... 36

References ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

3 Meniere's Disease ................................. 41 The Clinical Syndrome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Aetiology and Pathology ............................ 44 Management ...................................... 47 Vestibular Drop Attacks (Tumarkin's Otolithic Crisis) ... 51

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

x Contents

4 Perilymph Fistulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Aetiology and Pathomechanisms ..................... 57 Endolymphatic Hydrops and Perilymph/Endolymph

Fistulas ......................................... 59 How Maya Perilymph Fistula Be Identified? ........... 59 Management ...................................... 61

Tullio Phenomenon .................................. 62 Otolith Tullio Phenomenon . . . . . . . . . . . . . . . . . . . . . . . . . . 63

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

5 Miscellaneous Vestibular Nerve and Labyrinthine Disorders ........................................... 71 Unilateral Vestibular Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Bilateral Vestibular Loss .............................. 77

Management ...................................... 81 References .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Section B CENTRAL VESTIBULAR DISORDERS.... 85

6 Vestibular Epilepsy ................................ 91 Epileptic Nystagmus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Vestibular versus Visual (Optokinetic) Seizures. . . . . . . . . 94 "Vestibulogenic Epilepsy" .......................... 95

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

7 Downbeat NystagmuslVertigo Syndrome. . . . . . . . . . . . . . 99 The Clinical Syndrome: Nystagmus, Oscillopsia and

Postural Imbalance ............................... 99 Pathomechanism and Site of the Lesion. . . . . . . . . . . . . . .. 102 Aetiology ......................................... 103 Management ...................................... 105

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 106

8 Upbeat NystagmuslVertigo Syndrome ................ 109 The Clinical Syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 109 Pathomechanism and Site of the Lesion . . . . . . . . . . . . . . .. 111 Aetiology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 114 Management ...................................... 114

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 115

9 Ocular Tilt Reaction ............................... 117 The Clinical Syndrome ... . . . . . . . . . . . . . . . . . . . . . . . . . .. 117 Alternating Skew Deviation, See-saw Nystagmus and

Ocular Tilt Reaction ... . . . . . . . . . . . . . . . . . . . . . . . . . .. 119 Pathomechanism of Ocular Tilt Reaction .............. 120

Contents xi

Topographical Specificity of Ocular Tilt Reaction ....... 120 Aetiology ......................................... 126 Management ...................................... 127

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 127

10 Miscellaneous Central Vestibular Disorders. . . . . . . . . .. 129 Central Brainstem/Cerebellar Lesions Mimicking Vestibular

Neuritis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 129 Paroxysmal Central Vertigo ........................... 130 Falls Without Vertigo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 132 References ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 133

Section C POSITIONAL VERTIGO. . . . . . . . . . . . . . . . .. 135

11 Benign Paroxysmal Positioning Vertigo (BPPV) ....... 139 Mechanism of Cupulolithiasis ........................ 140 Aetiology ......................................... 143 Nystagmus ........................................ 143 Horizontal Semicircular Canal BPPV? . . . . . . . . . . . . . . . .. 145 Vertigo and Postural Imbalance ...................... 145 Management ...................................... 148

References ......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 150

12 Positional Nystagmus/Vertigo with Specific Gravity Differential Between Cupula and Endolymph (Buoyancy Hypothesis) ......................................... 153 Positional Alcohol Vertigo/Nystagmus (PAN) ............ 154 Positional "Heavy Water" Nystagmus . . . . . . . . . . . . . . . . . .. 156 Positional Glycerol Nystagmus ......................... 156 Positional Nystagmus with Macroglobulinaemia

(Waldenstr6m's Disease) ............................ 156 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 157

13 Vertigo and/or Tinnitus Associated with Neurovascular Compression "Vestibular Paroxysmia" (Disabling Positional Vertigo) ............................................ 159

Conclusions from a Confusing Literature .............. 161 References .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 162

14 Central Positional Vertigo ......................... 165 Positional Downbeating Nystagmus . . . . . . . . . . . . . . . . . . . .. 165 Central Positional Nystagmus .......................... 165 Central Positional Vertigo ............................. 166 "Basilar Insufficiency" ................................ 166 Head-extension Vertigo ... . . . . . . . . . . . . . . . . . . . . . . . . . . .. 167

xii Contents

Bending-over Vertigo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 169 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 169

Section D VASCULAR VERTIGO .................. 171

IS Migraine and Vertigo ............................. 175 Pathogenesis and Management . . . . . . . . . . . . . . . . . . . . . .. 176

Benign Paroxysmal Vertigo in Childhood (BPV) .......... 177 Benign Paroxysmal Torticollis in Infancy. . . . . . . . . . . . . . . .. 178 Benign Recurrent Vertigo (BRV) ...................... 179 Basilar Artery Migraine ............................... 180 Dizziness and Vertigo as Facultative Symptoms in Migraine.. 182 Association of Migraine with Other Vertigo Disorders? .... 183 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 184

16 Hyperviscosity Syndrome and Vertigo ............... 187 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 188

Section E TRAUMATIC VERTIGO ................. 189

17 Head and Neck Injury . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 193 Traumatic Otolith Vertigo. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 194 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 195

18 Vertigo Due To Barotrauma. . . . . . . . . . . . . . . . . . . . . . .. 197 Alternobaric Vertigo ................................. 197 Decompression Sickness .............................. 198 Round and Oval Window Fistula ....................... 199 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 200

Section F FAMILIAL VERTIGO AND VERTIGO IN CHILDHOOD ...................................... 201

19 Familial Periodic AtaxialVertigo . . . . . . . . . . . . . . . . . . .. 205 Management ...................................... 207

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 208

20 Vertigo in Childhood. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 209 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 211

Section G DRUGS AND VERTIGO ................. 213

21 Drugs and Vertigo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 215 Ototoxic Agents ..................................... 215

Contents xiii

Cerebellar Intoxication ............................... 219 Drugs and Eye Movements ............................ 223 References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 225

Section H NON-VESTIBULAR VERTIGO SYNDROMES ...................................... 229

22 Visual Vertigo ................................... 233 Circularvection and Linearvection: Optokinetically Induced

Perception of Self-motion ........................... 234 Psychophysics of Circularvection ..................... 236

Visual- Vestibular Interaction: Functional Significance of Visual and Vestibular Cortex ........................ 238

Rollvection-Tilt: Optokinetic Graviceptive Mismatch .... " 240 Visual Pseudo-Coriolis Effects and Pseudo-Purkinje Effect.. 242 Optokinetic Motion Sickness. . . . . . . . . . . . . . . . . . . . . . . . . .. 244 Physiological Height Vertigo and Posture ................ 245

Physical Prevention of Physiological Height Vertigo ..... 250 Licence for Workers on Heights? ..................... 250 The "Visual Cliff" Phenomenon. . . . . . . . . . . . . . . . . . . . .. 251

Vision and Posture ................................... 251 Moving Visual Scene ............................... 252 Visual Acuity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 253 Near Vision and Eye-Object Distance ................. 255 Visual Control of Fore-Aft versus Lateral Body Sway .... 256 Visual Stabilisation in the Dark . . . . . . . . . . . . . . . . . . . . . .. 256 Flicker Illumination ................................ 256 Visual Field ....................................... 257 Eye Movements, Oculomotor Disorders and Postural

Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 258 Nystagmus with Oscillopsia Impairs Balance ........... 259 Extra-ocular Muscle Paresis Impairs Locomotion and

Balance ....................................... " 260 Oscillopsia .......................................... 263

Oscillopsia is Smaller than Retinal Image Slip: Deficient Vestibulo-ocular Reflex ........................... 264

Acquired Ocular Oscillations with Oscillopsia .......... 266 Physiological Impairment of Motion Perception with

Moving Eyes .................................... 266 Normal (Physiological) Inhibitory Interactions Between

Self-motion and Object-motion Perception. . . . . . . . . .. 268 Pathological (Adaptive?) Binocular Impairment of Motion

Perception Caused by Monocular External Eye Muscle Paresis ......................................... 269

Oscillopsia and Motion Perception in Congenital Nystagmus ...................................... 269

XIV Contents

Conclusions ....................................... 271 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 271

23 Somatosensory Vertigo ............................ 277 Cervical Vertigo ..................................... 277

Functional Significance of Neck Afferents and Neck Reflexes ........................................ 278

Ataxia and Nystagmus in Experimental Cervical Vertigo 280 Clinical Evidence for Cervical Vertigo? . . . . . . . . . . . . . . .. 281

Somatosensory (Arthrokinetic) Nystagmus and Self-motion Sensation ......................................... 281

Vertigo and Postural Imbalance with Sensory Polyneuropathy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 284

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 285

Section I PSYCHOGENIC VERTIGO ................ 289

24 Psychogenic Vertigo .............................. 291 Organic versus Psychiatric Morbidity. . . . . . . . . . . . . . . . .. 291 Vestibular Dysfunction in Psychiatric Disorders? . . . . . . .. 292 How May Psychogenic Vertigo Be Diagnosed? ......... 293 Anxiety Neurosis .................................. 294 Depression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 294 Agoraphobia ...................................... 295 Hysteria .......................................... 295 Post-traumatic Vertigo ............................. , 295 Intoxication ....................................... 295

Acrophobia ......................................... 296 Psychotherapy of Acrophobia and Agoraphobia ........ 297

Phobic Postural Vertigo ..... . . . . . . . . . . . . . . . . . . . . . . . . .. 298 Clinical Features of Phobic Postural Vertigo. . . . . . . . . . .. 298 Fear of Impending Death .. . . . . . . . . . . . . . . . . . . . . . . . . .. 299 Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 300 Primary Personality ................................ 301 Therapeutic Regime. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 301 Is Phobic Postural Vertigo a Disorder of Space Constancy

due to Uncoupling of the Efference Copy? ........... 302 Differentiation of Phobic Postural Vertigo Attacks from

Acrophobia and Agoraphobia. . . . . . . . . . . . . . . . . . . . .. 303 References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 304

Section J PHYSIOLOGICAL VERTIGO ............. 307

25 Motion Sickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 311 The Clinical Syndrome. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 311

Contents xv

Nausea and Vomiting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 312 Labyrinth Function and Motion Sickness. . . . . . . . . . . . . .. 312 The Visual- Vestibular Conflict (Mismatch) ............ 313 Incidence and Susceptibility ......................... 316 Management: Physical and Medical Prevention ......... 317

Space Sickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 319 References ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 320

Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 325

Glossary

Acrophobia: fear of heights, when "physiological height vertigo" induces a conditioned phobic reaction characterised by a dis­sociation between the objective and the subjective risk of falling.

Agoraphobia: fear of wide open spaces or public places with excess anxiety, dizziness and postural imbalance.

Alternobaric vertigo: transient vertigo due to pressure changes in the middle ear; it primarily affects divers and aircrew.

Arthrokinetic nystagmus: movements of the limbs which may induce a compelling illusion of self-motion and a purely so­matosensory nystagmus in stationary subjects.

Basilar artery migraine: migrainous vasoconstriction within vertebrobasilar territory; it occurs predominantly in adolescent girls.

Benign paroxysmal positioning vertigo (BPPV): most common form of vertigo which is caused by cupulolithiasis onto the cupula of the posterior semicircular canal. It is precipitated by rapid head extension or lateral head tilt which evokes an en­hanced post-rotatory positioning response rather than a pos­itional response.

Benign paroxysmal vertigo in childhood (BPV): most common episodic vertigo in childhood; based on a migrainous mech­anism.

Benign recurrent vertigo (BRV): recurrent vertigo attacks pre­sumably based on a migrainous mechanism in adults.

Buoyancy hypothesis: positional nystagmus and/or vertigo with specific gravity differential between cupula and endolymph (e.g., positional alcohol nystagmus; positional heavy water nystagmus).

XVllI Glossary

Cervical vertigo: vertigo and unsteadiness of gait induced by stimulation of, or lesions in, neck afferents.

Circularvection/linearvection: optokinetically induced perception of apparent self-motion.

Coriolis effect: spatial disorientation, with nausea, through cross­coupled accelerations, when the head is undergoing a rotation about one axis and is tilted about a second axis.

"Disabling positional vertigo": vertigo associated with neuro­vascular cross-compression at the root entry zone of the eight cranial nerve (better called "vestibular paroxysmia"?)

Downbeat nystagmus/vertigo syndrome: central disorder of the vertical vestibulo-ocular reflex in pitch with downbeat nystagmus, oscillopsia, and postural imbalance.

Familial periodic ataxia/vertigo: rare disabling condition of auto­somal dominant inheritance which manifests either as recurrent attacks of unsteadiness of gait and stance or as attacks of vertigo and nystagmus.

Head extension vertigo: physiological postural imbalance when the otoliths are beyond their optimal functioning range in the offending head-extended position.

Height vertigo: physiological "distance vertigo" through visual destabilisation of postural balance when the distance between the subject's eye and the visible stationary surroundings be­comes critically large.

Hyperviscosity syndrome: pathological hyperviscosity of the blood (associated with polycythaemia, hypergammaglobulinaemia, or Waldenstrom's disease) can cause vertigo by vascular obstruction of the venules of the labyrinth.

Lateropulsion: irresistible lateral falls of patients with acute brain­stem lesions (e.g., Wallenberg'S syndrome) mostly without sub­jective vertigo.

Meniere's disease: endolymphatic hydrops with the classical triad of fluctuating hearing loss, tinnitus and attacks of vertigo (fourth commonest cause of vertigo).

Motion sickness: distressing syndrome with nausea and vomiting induced by unfamiliar bodily accelerations in vehicles to which the person has not adapted or by intersensory mismatch involving conflicting vestibular and visual stimuli.

Ocular tilt reaction: disorder of the vestibulo-ocular reflex in roll; eye-head synkinesis consists of lateral head tilt, skew deviation and cyclorotation of the eyes.

Optokinetic motion sickness: symptoms of motion sickness when viewing large moving visual scenes (simulator sickness).

Oscillopsia: apparent movement of the visual scene due to in­voluntary retinal slip in acquired ocular oscillations or deficient vestibulo-ocular reflex.

Glossary xix

Paroxysmal dysarthria/ataxia: non-epileptic manifestation of paroxysmal attacks in multiple sclerosis by ephaptic activation of adjacent demyelinated axons.

Perilymph fistula: rupture of the otic capsule, usually at the oval or the round window, which causes perilymph leakage and abnormal transfer of pressure changes.

Phobic postural vertigo: attacks of postural vertigo and unstead­iness of gait with accompanying or subsequent anxiety distin­guishable from agoraphobia and acrophobia; a psychogenic dis­order of "space constancy" due to uncoupling of the efference copy signal (third commonest cause of vertigo).

Positional vertigo: vertigo induced by changes in head position relative to the gravitational vector; in positioning vertigo head movement rather than head position is the precipitating factor.

Purkinje effect: tumbling sensation of turning about an off-vertical body axis when the head is tilted during a post-rotational semi­circular canal response.

Space sickness: motion sickness in astronauts induced by head movements in weightlessness.

Thalamic astasia: postural imbalance in acute thalamic lesions without motor weakness, sensory loss or cerebellar signs.

Traumatic otolithic vertigo: traumatic dislocation of otoconias resulting in unequal loads on the macular beds which causes transient head motion intolerance (oscillopsia and postural im­balance).

Tullio phenomenon: pathological sound-induced vestibular symptoms (e.g., in patients with perilymph fistulas).

Upbeat nystagmus/vertigo syndrome: central disorder of the vertical vestibulo-ocular reflex in pitch with upbeat nystagmus, oscillopsia and postural imbalance.

Vestibular atelectasis: collapse of the walls of the ampulla and utricle with unilateral or bilateral vestibular dysfunction.

Vestibular drop attacks (also called Tumarkin's otolithic crisis): reflex-like vestibulospinal loss of postural tone in endolymphatic hydrops (e.g., Meniere's disease).

Vestibular epilepsy: episodic vertigo secondary to focal discharges from the vestibular cortex.

Vestibulogenic epilepsy: variety of seizures induced by vestibular stimulation or dysfunction.

Vestibular neuritis: acute viral infection of the vestibular nerve with partial unilateral vestibular paralysis (second commonest cause of vertigo).

Visual cliff phenomenon: innate visual depth avoidance without former experience of falling off edges.

Visual vertigo: spatial disorientation and postural imbalance in­duced by unusual visual stimulation or visual dysfunction.