Our initial report also indicated that there are physical findings associated with MdDS that can help make the diagnosis. All of the patients rocked, swayed, or bobbed at an average frequency of ∼0.2 Hz (one cycle every 5 seconds). Many of the patients had lateral movement on the Fukuda Stepping Test, and some had vertical nystagmus, with quick phases of the nystagmus upward when the head was rolled to one side and downward when the head was rolled to the other side. They also had many associated physical complaints4 that are described in the Saha and Fife article.1 These signs caused these people to be truly miserable. Many were unable to work and those who managed to soldier on found that their efficiency was very low. Depression was common. Several tried to commit suicide after failing to get relief from years of continuous oscillation.
Based on the physical findings, our laboratory studies in monkeys, and an early survey of the disorder,5 we postulated that MdDS was based on maladaptation of velocity storage in the vestibulo-ocular reflex. Treatment is essentially based on using low-velocity full-field stimulation while rolling the head at the frequency of the rocking, swaying, or bobbing. The physical findings and associated somatic signs disappear after successful treatment.
As treatment has progressed, it has become clear that there are 2 ways that MdDS is initiated. We have termed one form “classic MdDS,” which follows cruises or travel on the sea, extensive car trips, or turbulent flights. This has been the easiest form of the illness to treat, and the treatment is most successful in this group. We call the second form “spontaneous MdDS,” which occurs when the rocking and associated signs develop without a preceding trip. In our recent study, these people were more difficult to treat and the cure rate was more than 50%.
Although vestibular testing can be of use, in general, MRIs, vestibular evoked myogenic potentials, auditory evoked potentials, and multiple blood tests really have nothing to offer diagnostically. The major diagnostic clues are a history of a previous cruise or flight or spontaneous onset and the rocking, swaying or bobbing at approximately 0.2 Hz (the frequency is generally higher after if the MdDS followed a flight or occurred spontaneously). A striking finding is that MdDS symptoms abate when riding in a car, plane, or boat but return promptly at the end of the ride.
Thus, MdDS is a treatable illness, and it is important that it be recognized as such by neurologists and otolaryngologists who see these patients in order to send them for potential reduction or cure of their symptoms and signs.