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Mal de Debarquement Syndrome You return from a cruise ship vacation and find that when you step onto dry land, you feel as if you are still on a rocking ship. You have had this sensation briefly before, so you expect that it ­ will resolve, but it ­ doesn’t. You feel unsteady on your feet, but you are able to go on with routine activities. Curiously, you feel best when you are in motion, such as riding in an automobile. Although the symptoms temporarily remit while in motion, they are worse when you stop moving. Mal de debarquement syndrome (MdDS) is defined by a per­ sis­ tent feeling of motion—­ usually with an ele­ ment of slowly rocking from side to side—­ and a sense of imbalance while walking. MdDS usually occurs ­ after exposure to motion, most commonly on a ship, airplane, or long ­ ride in an automobile. Many ­ people who have sailed on a ship have noted the per­ sis­ tence of a sensation of rocking ­ after disembarking that lasts for minutes to hours. This is usually considered to be a normal phenomenon. For the person with MdDS, though, the rocking sensation may continue for months or even years. When a person with MdDS is in motion, riding in an automobile , for instance, the rocking sensation temporarily stops. However, once the person leaves the vehicle and is again sitting or standing still, the feeling of rocking returns and is CHAPTER  8 Constant Dizziness for Months, Years 132 often temporarily worse. For unknown reasons, this disorder is more common in ­ women than in men and is associated with anxiety disorders and migraine. Ge­ ne­ tic susceptibility may be an impor­ tant ­ factor for developing the syndrome. While the exact mechanism of MdDS is unknown, most experts believe this syndrome has something to do with how the brain adapts to motion. The types of motion one feels on a ship are complex. It is common, for example, for a person standing on the deck of the ship to experience roll to the right and the left combined with heaving up and down. One theory suggests that while on a ship, in a vehicle, or in any situation in which the person is constantly in motion, the brain in some fashion learns to associate feelings of continuous motion with turning of the head from side to side, as when looking off the deck of a ship to search the ­ water for dolphins or turning the head to look around the pool for the snack bar. When a ship passenger returns to land, the brain recalls the previously learned association and produces a feeling of rocking that mimics what was pres­ ent on the ship. In our modern world the brain is constantly adapting to dif­ fer­ ent motion experiences, and usually it does so with ­ little difficulty. Sometimes it can take a while for the brain to make the adjustment, but eventually it does. However , with MdDS for some reason the brain becomes “stuck” in a constant motion mode. If a normal person is spun around multiple times on a rotating chair and then suddenly stopped, she ­ will have a per­ sis­ tent ­ after-­ sensation of rotation that ­ will gradually dwindle. The rate of the decay is defined by a vestibulo-­ ocular reflex (VOR) time constant, the time it takes for the sensation to decay to 63 ­ percent of the initial magnitude. The signal of rotation is picked up by the semicircular canals in the inner ear Mal de Debarquement Syndrome 133 and passed on the nerve cells in the brain where reverberating cir­ cuits prolong the sensation well beyond the duration of the signal generated in the inner ear (often called velocity storage ). The normal VOR time constant can range from 5 to 40 seconds. VOR time constants can be mea­ sured by a test your doctor can order called rotational testing in the dark, also known as rotatory chair testing (see chapter 5). It has been suggested that ­ people with longer time constants are more susceptible to MdDS. In other words, overactivity within ­ these reverberating central vestibular pathways may be a ­ factor in developing MdDS. Prolonged repetitive rotations and certain drugs can shorten the time constant and possibly improve MdDS, but so far ­ there have not been any controlled treatment­ trials using ­ these techniques.­ There is a consensus that tests of inner ear function, both auditory and vestibular, are generally normal in patients with MdDS, and scans of the brain...


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