Neuro-Otologia Diagnostico Y Manejo De Problemas

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NEURO-OTOLOGY: LABORATORY INVESTIGATIONS IN DIAGNOSIS AND MANAGEMENT OF NEUROOTOLOGICAL DISORDERS
Kevin A. Kerber and Robert W. Baloh

Investigations 741 Vestibular Testing Imaging 747

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Treatment of Neuro-otological Disorders 747 Management of Patients with Vertigo 747 Management of Patients with Hearing Loss and Tinnitus

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Neuro-otology is amultidisciplinary specialty with primary training stemming from either otolaryngology or neurology, but most practitioners are otolaryngologists whose emphasis is on surgical approaches to disorders of the ear. As described in Chapter 18, many neurological disorders manifest with dizziness, and neurologists have become increasingly involved in evaluating patients with this common symptom. Because thevestibular system is intimately associated with the control of eye movements, ocular motor measures are central to the laboratory evaluation of patients with dizziness. Few tests of the vestibular system can be conducted without using the corresponding movements of the eyes as the surrogate marker. Because the peripheral vestibular and auditory systems are closely related anatomically, an understandingof the auditory system, coupled with familiarity with the appropriate laboratory measures for its assessment, will greatly enhance the clinician’s ability to evaluate patients with complaints of dizziness.

INVESTIGATIONS Vestibular Testing
Eye Movement Recording
The earliest measures of eye movement recording were made using electro-oculography (EOG). This technique utilizes the potentialdifference between the cornea and the retina, known as the corneal-retinal potential, which acts as an electric dipole, oriented in the direction of the long axis of the eye (Baloh and Honrubia, 2001). When electrodes are placed in the vicinity of the eyes, this potential becomes more positive when the eye

rotates toward it and less positive when it rotates in the opposite direction. Recordings aremade with a three-electrode system, using differential amplifiers. Two of the (active) electrodes are placed on each side of the eye, and the reference (ground) electrode is placed somewhere remote from the eye. The two active electrodes measure a potential change of equal amplitude but opposite in direction. The difference in potential between these electrodes is amplified and used to control thedisplacement of a pen-writing recorder or similar device to produce a permanent record. Because the emphasis of this study initially was on recording nystagmus, this test also is referred to as electronystagmography (ENG). Of the newer techniques for recording eye movements, video-oculography (VOG) is becoming popular in clinical use; another newer technique, the magnetic search coil technique,remains primarily a research tool. Each technique has advantages and disadvantages. EOG probably still is the most widely used for recording eye movements. The equipment is less expense to purchase, and the test provides reliable clinical information when performed by clinicians with proper training (Furman et al., 1996). Artifacts from lid movements or muscle action potentials are common; thus, the“noise” is greater in ENG than in either VOG or the magnetic search coil technique, and measuring torsional eye movements is difficult. Probably the main clinical advantage of VOG is the ability to go back and observe the actual video recording of the eye movements. This becomes particularly helpful in trying to distinguish an actual eye movement from an artifact such as a blink. Measuringtorsional eye movements also is possible with VOG. Disadvantages of VOG are the inability to measure eye movements with the eyes closed and difficulties stabilizing the head gear. 741

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Neurological Investigations and Related Clinical Neurosciences

The magnetic search coil technique uses a contact lens embedded with two coils of wire. One coil is wound in the frontal plane to...