Nonvestibular Dizziness

Balance and spatial orientation depend on three main systems: the vestibular apparatus, vision, and proprioception (position sense from the spine and pressure sensors of the extremities). Dizziness may result from problems involving any one, or more, of these systems. Furthermore, disease processes of other bodily systems, such as circulation, respiration, cerebration (including anxiety), and endocrine function, may cause dizziness by affecting the former ones! Numerous types of nonvertiginous dizziness may occur, and the more notable types will be discussed briefly. Again, emphasis should be placed on eliciting an accurate descriptive history from the patient.

A patient may be "lightheaded," feel vaguely disoriented, have visual blurring, become faint, lose consciousness (experience syncope), or have disequilibrium. Certain positions or activities might bring on the symptoms. Anxiety, with hyperventilation, may be present. Postural changes, moving the neck, or using the arms may be precipitating factors. The time line is also important. Some patients are vaguely dizzy around the clock for days, and others have symptoms during more specific time periods. These historical points will help to narrow down the differential diagnosis.

When a patient experiences syncope, end-organ inner ear disease can be ruled out; do not call the ear specialist first. Peripheral labyrinthine disease often puts the patient to bed with sickening discomfort, but it will never, by itself, cause loss of consciousness. Real syncope results from impaired oxygenation of the brain, by way of vascular compromise, blood pressure drop, hypoxemia, or cardiac arrhythmia. Faintness, or near-syncope, is closely related.

A workup of older syncopal patients should include Holter monitoring and blood pressure readings, both supine and erect. Postural hypotension may be occurring. Brainstem ischemia, cerebrovascular disease, or subcla-

vian steal syndrome might also be the cause. With younger patients, a good history may reveal that just anxiety, with resulting hyperventilation, caused the event. Look for sudden psychogenic vasovagal reactions as well, which may even be accompanied by seizure-like activity.

Blurring of vision does not relate to the vestibular system, and patients with this complaint deserve an eye workup. Other symptoms may be less specific. General disorientation or lightheadedness may be a sign of metabolic disease, for example, diabetes, nutritional disorders, or hypothyroid-ism. The more vague the symptoms and their time-line become, the more likely it is that stress, fatigue, or just plain psychiatric illness is the cause. However, a neurologic lesion may be the underlying cause. Certainly, when there is doubt about a source of dizziness, the urge to document things with a CT scan or MRI comes into play. The expense is great, but the reassurance value might make it worthwhile. Medicolegal considerations often oblige us to perform these expensive but reassuring studies.

We have mentioned some of the nonvestibular causes of dizziness. The purpose of this last chapter, however, is to describe disorders of the vestibule (utricle, saccule, and semicircular canals), vestibular nerve, and vestibular nuclei in the brainstem. A key point regarding these areas is that their diseases produce either vertigo or disequilibrium.

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