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Department of Neurology, The Mount Sinai School of Medicine, New York, New York, USA
1Correspondence: E-mail: bernard.cohen{at}mssm.edu
BENIGN PAROXYSMAL POSITIONAL vertigo (BPPV) is a powerful sense of pitching forward when the head is moved into dependent positions. It is associated with the presence of tiny calcium carbonate stones (otoconia) in the semicircular canals. The discovery that this vertigo can be cured by appropriately positioning the head was based on understanding the anatomy and physiology of the peripheral vestibular system and the vestibulo-ocular reflex. Since the vestibular labyrinths of vertebrates have not been altered for millions of years, this vertigo was probably present well before the common era and may even account for some of the roars in the forest that dinosaurs gave off—at least in films!
The vestibular labyrinth is one of nature’s most successful experiments; the sensitivity and range of the receptors to angular and linear acceleration is remarkable, and the current structures of the semicircular canals and otolith organs have been around for a long time. The lamprey, an early vertebrate has two canals, but the system evolved, and sharks, which appeared approximately 450 million years ago, have a three-canal system similar to humans and all other mammals (1)
. Clarke recently published a reconstruction of the labyrinth of a brachiosaurus (2)
(Fig. 1
), and demonstrated that the three semicircular canals have the same, "orthogonal" orientation as our own canals with an extension of the labyrinth below that presumably contained the otolith organs, the saccule and utricle. In each species, the canals are duplicated on the opposite side and work in a push-pull manner, so that all angular head motion is converted into three vectors, which are widely represented in the brainstem, cerebellum, and subcortical visual system. Thus, although we see the world predominantly in horizontal and vertical directions with our cerebrum, our hindbrain continues to process information in the same canal-coordinate system as that of the brachiosaurus who lived approximately 165 million years ago.
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As with every structure, however, things sometimes go wrong. Let’s consider the the plight of a typical patient whose system went very wrong, indeed. This middle-aged woman rolled over in bed one night and awoke with a sense of pitching forward violently. The world swam vertically before her eyes. She began to sweat, became nauseated, and screamed. The sensation gradually abated over about a minute. She was fine if she lay perfectly still, but head movement again brought on the frightening symptoms. After she had gingerly gotten out of bed, she could walk, but if she looked up or bent over, she again brought on the disabling symptoms. Was this a brain tumor or a stroke? From the severity of the symptoms, it was clearly serious.
The latency, duration, and association with a specific head position in a postmenopausal woman, and the fact that her balance was normal between episodes indicated to her physician that the vertigo was produced by neither a tumor nor a stroke. She could be cured by simple positional reorientation. The initial stage of the treatment was to move her head into the position of maximal discomfort, which for her was a left-side down, head-hanging position with the left mastoid dependent. In that position, she again felt that she was uncontrollably falling forward, although she was lying flat, firmly supported on the examining table. Two minutes after the symptoms had disappeared, she was rolled onto her right side with her right forehead down and her left mastoid up. Again, she became very dizzy. Several hours later, however, she was able to move into any position without experiencing the whirling vertigo, and she was cured. In some patients, a single similar treatment has cured vertigo that has been present for years. The condition is called benign paroxysmal positional vertigo (BPPV), and it is one of the commonest causes for vertigo.
Given that nothing is new, could BPPV have been present earlier—much earlier, even in the dinosaurs? Two facts support this speculation. We know that the same canal/otolith system is present in both vertebrate species. These large beasts are also believed to have bent their heads toward the ground and to reach high into the trees, presumably to take leaves from the top branches. Therefore it is possible that some of the roars from the forest in Jurassic Park were actually cries of distress because the dinosaurs felt that they were pitching forward uncontrollably (3)
.
Regardless of whether this condition is 165 million years old, it must certainly have been present in times before the Common Era in the relatively few people that lived beyond the age of 50. Vertigo due to vestibular disease in Greece was thought to be a prodrome of epileptic seizures (4)
. Since physicians of the earlier times were also priests, in addition to bleeding, purging, scarification, vomiting, and the administration of drugs, physicians of earlier eras utilized prayer and incantations over patients who were seriously ill to drive out the evil spirits (5
, 6)
.
The cure for BPPV was discovered almost simultaneously about 20 years ago by Epley, a Portland otolaryngologist, Semont, Fryss, and Vitte, a French team, and by Parnes and McClure, Canadian surgeons (7
8
9)
. Treatment grew out of the understanding that when the posterior semicircular canal nerve was electrically stimulated, the eyes moved precisely in the plane of that canal, similar to the eye movements during BPPV (10
11
12
13)
. This was followed by the demonstration by Schucknect that densely stained material was lodged next to the cupula and hair cells in the posterior canal of a man with paroxysmal vertigo (14)
. Epley, Semont, Parnes, and the others reasoned that otoconia from the maculae of the otolith organs, the saccule and utricle, had fallen into the posterior semicircular canal (15)
. Before entry of the otoconia, the hair cells of the posterior canals moved only during angular head movements in response to the vector of angular acceleration in the plane of that canal. Afterwards, the canal not only responded to angular acceleration but also to the fall of the otoconia in the endolymph toward gravity, which also produced deflection of the hair cells. Thus, the semicircular canal had been converted from an organ that had sensed only angular head movement into both a rotational and gravity-sensing mechanism. The treatment was relatively simple: first move the head so that the crystals fall away from the cupula toward the middle of the canal, then reverse the head position with regard to gravity, so that the crystals move out of the canal into the vestibule of the labyrinth, where they attach to the wall and are reabsorbed.
Displacement of the otoconia from the saccular and utricular maculae can occur after head injury, but it is most commonly present spontaneously in postmenopausal women. The otoconia, which in the young are perfect tetrahedrons, composed of calcium carbonate in a protein matrix (16
, 17)
, become eaten away with advancing age (17)
, and form a CaCO3 "sand," which has a higher specific gravity than the surrounding endolymph (9)
. Hence, the "sand" has the ability to seek gravity in appropriate head positions, deflecting the hair cells in the semicircular canals. The 45 s to 1 min duration of the symptom reflects activation of central circuits in the vestibular system that prolong the impulsive response from the canals (18)
. The breakup of the otoconia may reflect a problem with calcium metabolism, representing an "inner ear osteoporosis" of sorts. But calcium levels have never been abnormal in these women, and BPPV is not associated with generalized osteoporosis. The problem could equally be in maintenance of the protein matrix—we simply don’t know. There is a weak familial tendency in this condition, suggesting the importance of genetic mechanisms in producing the "sand" (19)
. Indeed, the otoconia are controlled by the NOX3 gene and knockout "tilted" mice have been prepared with absent otoconia (20)
.
At least two lessons can be gleaned from this. First, the description of the exact relationship of the eye movements to the posterior canals during such vertigo came as a result of basic physiological studies—once again demonstrating that precise knowledge of the physiology and anatomy frequently precede curative interventions. Bravo for Congress and the NIH for making this possible over the last 50 years! Second, before microscopes, biochemistry, and basic understanding of this condition, one prevalent theory of seizures in ancient eras was that evil spirits had invaded the brain to produce these violent symptoms. Now, the condition is known as benign paroxysmal positional vertigo, and it is generally considered useless to waste time ordering an MRI to rule out a stroke or tumor when the patient can be cured by simply positioning the head in the canal planes—a good example of the retreat of attribution to the supernatural in the face of knowledge (21)
. Sic transit gloria mundi!
FOOTNOTES
The opinions expressed in editorials, essays, letters to the editor, and other articles comprising the Up Front section are those of the authors and do not necessarily reflect the opinions of FASEB or its constituent societies. The FASEB Journal welcomes all points of view and many voices. We look forward to hearing these in the form of op-ed pieces and/or letters from its readers addressed to journals{at}faseb.org.
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