Disequilibrium and Vertigo

The vestibular organ (semicircular canals, saccule, and utricle) plays a central role in the regulation of balance. Disturbances of the vestibular apparatus (composed of the vestibular organ, the vestibulocochlear n., and the vestibular nuclei of the brainstem) cause dysequil-ibrium, the main symptom of which is vertigo. It must be emphasized, however, that vestibular disturbances are just one cause of vertigo (see below) and not even the most common one.

Regulation of equilibrium. Equilibrium (balance), i. e., the optimal static and dynamic mechanical stability of the human being in space, is maintained by the following neural processes:

• impulses from the vestibular apparatus concerning the position, movement, and acceleration of the individual in space;

• impulses from the visual system concerning the body's relation to visual space;

• impulses from the exteroceptive pathways concerning the body's contact with underlying surfaces (floor, mattress, etc.);

• impulses from the proprioceptive pathways concerning the positions of the joints and the spatial relations of the parts of the body to each other;

• impulses concerning movements in the process of being executed, from the pyramidal, extrapyramidal, and cerebellar systems;

• conscious (cognitive) and unconscious (emotional) influences;

• finally, the integration of all of these signals in the brainstem.

The various components of the regulation of balance are depicted schematically in Fig. 11.21.

Fig. 11.21 The maintenance of balance by integration of information from multiple channels

Disturbances of the regulation of equilibrium. Vertigo arises if individual informational and/or control components of the regulatory system are lost (see below), if the information coming through different sensory channels seems to be incompatible (so-called multisensory mismatch, e. g., in seasickness), or the sensory input is highly unusual (e. g., uncommon visual input from a great height). So many different structures play a role in the maintenance of equilibrium and their interactions are so complex, that the causes of vertigo are, understandably, highly varied. Different types of vertigo result from lesions at different sites.

Types of vertigo. Directional vertigo (vestibular vertigo) is characteristic of lesions of the peripheral portion of the vestibular apparatus, i. e., the vestibular organ and/or the vestibulocochlear n. The patient perceives the

Table 11.10 Differentiation of peripheral vestibular, central vestibular, and nonvestibular vertigo

Signs and symptoms

Nausea, vomiting, diaphoresis

Vertigo—intensity

Vertigo—type

Nystagmus

Hearing loss, tinnitus Other neurological deficits peripheral vestibular (labyrinth, nerve)

severe marked in a specific direction spontaneous nystagmus of vestibular type usual unusual

Type of vertigo central vestibular moderate moderate directional to some degree spontaneous nystagmus of vestibular type unusual usually present nonvestibular mild mild not in any specific direction nonvestibular nystagmus, or no pathological nystagmus absent the neurological examination may or may not yield positive findings environment as if it were in motion (= oscillopsia), e. g., rotating or heaving up and down like the deck of a boat. Vestibular vertigo is often accompanied by autonomic manifestations, such as nausea and vomiting, and by nystagmus. Central vestibular lesions (i. e., lesions of the vestibular nuclei in the brainstem) also cause directional vertigo, which is generally less intense than that due to peripheral lesions. The autonomic manifestations, too, tend to be milder or absent.

Nonvestibular vertigo is nondirectional and often difficult for the patient to describe. The patient may report a woozy feeling, emptiness in the head, or darkness before the eyes. Oscillopsia is absent and there are usually no autonomic manifestations. Central nervous lesions can cause pathological nystagmus, as listed in Tables 11.1,11.2. Nonvestibular vertigo is caused either by a lesion of the nonvestibular parts of the regulatory system for balance, or else by faulty information processing within the central nervous system (e. g., because of a cerebellar lesion). Pathological processes outside the central nervous system, such as orthostatic hypotension or aortic stenosis, can also cause nonvestibular vertigo.

The characteristic features of peripheral and central vestibular vertigo and of nonvestibular vertigo are summarized in Table 11.10.

Special aspects of history taking and diagnostic evaluation. The clinician should be able to tell whether the patient is suffering from vestibular or nonvestibular vertigo based on a meticulously elicited clinical history alone. It is also important to determine whether the vertigo is episodic or continuous and to ask about any precipitating factors (e.g., changes of position or particular situations that make the vertigo worse). If the vertigo worsens in the dark or when the patient's eyes are closed, the cause is likely to be a disturbance of proprio-ception (polyneuropathy, posterior column disease) or a bilateral vestibulopathy. The examiner should also always ask about accompanying symptoms (in particular, autonomic symptoms, tinnitus, hearing loss, and prior illnesses and infections). The history combined with the physical findings (nystagmus, results of balance tests, any other neurological abnormalities) usually allows localization of the functional disturbance. Further testing

(e. g., caloric testing of the vestibular organ, ENT consultation, neuroimaging of the head) mainly serves to determine the etiology.

We will now describe the main neurological causes of vertigo, particularly vestibular disturbances, in greater detail.

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