Describe motion sickness and mal de debarquement syndrome.

Motion Sickness

• Motion sickness is the syndrome of nausea, vomiting, pallor, sweating and malaise provoked by real or apparent motion.
• It arises from sensory conflict — a mismatch between the vestibular, visual and proprioceptive inputs, or between what is experienced and what is expected.
• The sensory conflict theory explains every situation in which it occurs, and giving examples demonstrates it: reading in a moving car, where the vestibular system signals motion and vision does not; being below deck in a ship, the same conflict; a flight simulator or virtual reality headset, where vision signals motion and the vestibular system does not — the reverse conflict; and a passenger being worse than the driver.
• The final common pathway is the vomiting centre, reached from the vestibular nuclei via the cerebellum and the chemoreceptor trigger zone, with histamine (H1) and muscarinic receptors mediating the response — which is precisely why antihistamines and anticholinergics work
• Susceptibility — greatest between 2 and 12 years, declining thereafter; rare under 2, before the vestibular system matures; greater in women, particularly during menstruation and pregnancy; and greater in migraine sufferers, in whom it is strongly associated. Patients with NO vestibular function do not get motion sickness, which is the strongest evidence for the vestibular origin

Mal De Debarquement Syndrome

• Mal DE debarquement ("sickness of disembarkation") is a persistent sensation of rocking, swaying or bobbing that begins after a period of passive motion — classically after a sea voyage or a long flight — and persists for weeks to months after returning to land
• A brief version is normal and universal: everyone feels the ground moving for a few hours after a boat trip. The syndrome is diagnosed when it persists beyond about a month
• The pathognomonic feature, and the one that makes the diagnosis, is that the symptoms are relieved by RE-exposure to passive motion — the patient feels better while driving or in a car and worse when still. This is the reverse of every other vestibular disorder, in which movement makes things worse, and it is the single question that identifies the condition
• It is thought to represent a maladaptive persistence of the vestibulo-ocular adaptation acquired during the voyage — the brain having recalibrated for a moving platform and failing to recalibrate back
• Epidemiology — strongly predominant in women in the fourth to fifth decade, and associated with migraine and with hormonal factors