2 See the author in lectures on Nerv. Diseases, Disorders of Sleep, p. 63, 2d ed.
DIAGNOSIS.—Vertigo is of course, as a rule, only a complex symptom of one or more numerous conditions. Acute isolated fits of vertigo are sometimes puzzling, because epilepsy may be preceded by brief vertigo and exist without notable spasms. Time may bring to us a frankly expressive epilepsy to explain former and less distinct fits. But usually it is the attacks of vertigo which are the causes of doubt. A man has sudden giddiness, and falls unconscious for a moment. These attacks persist. How shall we know them as vertigo? how be secure that they be not some form of the lesser epilepsy? As a rule, if they be vertigo there will be nausea or emesis, while the intervals between attacks will offer the usual signs of confusion of head, fear of losing balance, and all the numerous evidences of disturbed and easily excitable states of the sensorium—conditions rare in the interepileptic periods. The effect of bromides may aid the diagnosis, for, although often of use in vertigo, they have not such power to inhibit the fits as they possess in epilepsy. Persons long liable to any form of vertigo can readily cause attacks, or at least vertiginous feelings, by closing the eyes while standing, by the least rotation, or by putting a prism on one eye, so that among these tests we may frequently find the material for a diagnosis, which will of course, in many instances, be made easy enough by the presence of causes obviously competent to occasion the one or the other disease.
PROGNOSIS.—In true vertigo, if we exclude the organic causes, and especially intracranial neoplasms, there is very little to be feared. Deaths have been seen in Menière's disease, but are most rare. Even in grave examples of labyrinthine vertigo there is a probability that the worst which can occur will be deafness, and that vertigo will gradually cease as the delicate neural tissues become so degenerated as to cease to respond to irritations.
The DURATION of other forms of vertigo it is less easy to predict. Ocular vertigoes get well soon after the eye trouble is corrected, and the like is true of most vertigoes due to peripheral causes. So also the giddiness which is sometimes seen as a very early symptom in locomotor ataxia is transient, and will be apt, like the ocular and bladder troubles which mark the onset, to come and go, and at last to disappear entirely. It is to be remarked that vertigo at the beginning of posterior sclerosis is common, and is not due to ocular motor conditions.
Sometimes in vertigo, as in epilepsy, the removal of a long-existing cause may not bring about at once a cessation of the abnormal symptoms its activity awakened, so that it is well, as to the prognosis of duration, to be somewhat guarded in our statements. Nor is this need lessened by the fact that vertigo may be an almost lifelong infliction, without doing any very serious damage to the working powers of the person so disordered.
ETIOLOGY.—It is generally taken for granted that vertigo has always for its nearest cause some disorder of cerebral circulation; but while either active congestion or anæmia of brain may be present with vertigo, and while extreme states of the one or the other are certainly competent to produce its milder forms, it does not seem at all sure that they are essential to its being. Indeed, there is much reason to believe that vertigo is due in all cases to a disturbance of central nerve-ganglia, and that the attendant basal condition is but one incident in the attack.
In vertigo there are the essential phenomena, as disturbed balance, with a false sense of movement within or without, or of one's self. Then there are the lesser and unessential phenomena, which vary in kind and degree, and these are the moral and mental symptoms—terror, confusion of mind, and sensory illusions; and, last, the nausea and sickness met with here as in migraine, and the flow of clear, thin urine.
All of these symptoms should be accounted for in speaking of the intracranial organs, disorder of which causes vertigo. Ferrier has especially made it clear that equilibration involves afferent impressions, co-ordinative centres, and efferent excitations preservative of balance.
Guiding impressions, which direct the muscles through centres below the cerebrum, so as to aid in preserving our balance, reach these centres from the skin and the muscles, so that great loss of tactility or of the compound impressions called muscular sensations results in disturbance of equilibrium, but not in true vertigo, which is clinically this and something more.
A second set of impressions, of use in preserving equilibrial status, come through the eye, or rather habitually through the eyes, because the consensual impressions arising out of double vision and the co-ordinate movements of the two fields of sight have, as is well known, much to do in this matter. It is hardly needful to dwell on this point. Certain parts of the ear have, however, the largest share in maintaining our balance, and it seems likely that the semicircular canals—the part most concerned—although lying within the petrous part of the temporal and receiving nerves from the stem which constitutes the nerve of hearing, may have slight relations or none to the sense of audition.3 When the horizontal canals are cut, the head moves from side to side and the animal turns on his long axis. When the posterior or lower vertical canals suffer, the head sways back and forward, and the tendency is to fall or turn over backward. When the upper erect canals are cut, the head moves back and forward, and the tendency is to turn or fall forward.