A widespread and intricate illness called motion sickness develops in reaction to actual or imagined motion. The prevalence, symptoms, diagnosis and treatment for motion sickness are penned down in this article.

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Motion sickness

Motion sickness is a frequent ailment, with around 30% of the general population experiencing symptoms during a journey and 5% experiencing severe symptoms. It may manifest in a variety of ways, including digestive, central nervous system, and autonomic symptoms. Typically, nausea is the predominant symptom of motion sickness.

There is substantial individual variation in the sensitivity to motion sickness, as some persons may have symptoms with minimum provocation while in others it may be quite difficult to induce symptoms. Motion sickness develops when real v/s anticipated sensory stimuli do not correspond. Numerous countermeasures have been developed to prevent and treat this illness, while the specific neurobiological process is unknown.

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Prevalence

With a functional vestibular system and a strong provoking input, motion sickness may be induced in almost all persons. Patients whose labyrinths are completely dysfunctional are resistant to motion sickness. Individual susceptibility to sickness varies.

Some of the traits related to motion sickness are:

1. Females are more vulnerable than males.
2. Motion sickness starts at about age 6 and peaks at age 9; it declines throughout adolescence as a result of habituation.
3. Elderly individuals are least prone to motion sickness.
4. Cross-sectional studies indicate higher vulnerability in those with high aerobic fitness; it has been suggested that this is related to a more reactive autonomic nervous system.
5. Patients with vertigo, vestibular pathology, Meniere's disease, and migraines are at an increased risk.
6. Increased vulnerability is associated with hormonal variations during pregnancy and the menstrual cycle.

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Etiopathogenesis

Low-frequency lateral and vertical motion (e.g., air, sea, and road transportation) or virtual simulator motion frequently induce motion sickness (video games, virtual simulators). The notion of sensory conflict and neuronal mismatch is the most commonly accepted explanation for motion sickness. It depicts the conflict between the visual, vestibular, and somatosensory systems caused by actual or simulated motion.

Inputs from the visual and proprioceptive systems are also received by the vestibular nucleus of the brainstem, which receives afferents from the vestibular apparatus. Via the posterolateral thalamus, efferent projections subsequently reach the temporoparietal cortex, prompting autonomic responses and the vomiting centre. When there is a difference between the actual and predicted patterns of vestibular, visual, and kinesthetic inputs, motion sickness symptoms are triggered. Motion sickness typically occurs when the proprioceptive, vestibular, and visual inputs are conflicting or mixed.

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Symptoms

Motion sickness may cause a variety of symptoms, including the more typical ones like nausea and vomiting as well as less usual ones including cold sweats, pallor, headaches, sleepiness, yawning, lack of appetite, and increased salivation. Symptoms of motion sickness are often preceded by an inciting incident or exposure to an unusual motion. The term "sopite syndrome" is used to describe a group of symptoms that includes extreme sleepiness and exhaustion that lasts for many hours or even days after exposure. It could look as indifference, boredom, impatience, and personality changes to inexperienced observers.

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Diagnosis

1. Motion sickness is clinically diagnosed with a comprehensive history and physical examination. If a patient has a normal presentation or history of motion sickness, laboratory or radiographic testing is often unnecessary.
2. In a patient with a sudden onset of motion sickness symptoms, an evaluation for migraine headaches may be necessary due to their close association. The preventative treatment of migraines may not only reduce headaches but also ameliorate symptoms of vertigo and motion sickness.
3. Identifying life-threatening causes of motion sickness, such as basilar artery blockage, is critical. Occasionally, the early symptoms of basilar artery blockage are vertigo and motion sickness. These individuals often have additional sudden-onset symptoms, such as diplopia, dysarthria, dysphagia, and drop attacks. When basilar artery blockage is suspected, CT angiography must be performed to rule out basilar artery occlusion. Once this condition has been ruled out, one may next consider benign paroxysmal positional vertigo, vestibular migraine, vestibular neuritis, etc.

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Management

Behavioural therapy

The most effective treatments for motion sickness include behavioural countermeasures.

Among the short-term approaches are:

• Changes to the body's posture include the restriction of the head, shoulder, hip, and knee motion
• Avoiding reading when travelling
• Being positioned in a forward-facing seat, a front seat, or actively directing the vehicle
• Concentrating on a steady horizon
• attentive, controlled breathing
• Avoiding nicotine (if the patient is a smoker)
• Enjoying lovely music
• Avoiding travel in stormy or low-visibility circumstances

In the long run, habituation is the most effective countermeasure. It does not have the negative side effects of medication, such as sleepiness and impaired vision. Unfortunately, this time-consuming strategy may endure for several weeks, as illustrated by the military-run motion sickness desensitisation programs designed to cure pilots who cannot use anti-motion sickness meds. These programs are intended for long-term success since their success rates surpass 85 per cent. In the general population, motion sickness symptoms typically disappear after 24 to 72 hours of continuous exposure. Long-term habituation may not be accomplished if the intervals between exposures are more than one week.

Alternative treatments

Ginger, which works as an antagonist at the 5-HT3 receptor that plays a role in vomiting, is used in alternative therapies. In a small number of studies, acupressure bands applied to the P6 or Neiguan point on the anterior wrist were beneficial in the treatment of nausea and vomiting. However, additional data is required.

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Pharmaceutical treatment

Motion sickness medications are often partially effective and may have undesirable side effects. They are most effective when administered prophylactically or as soon as symptoms appear. Patients should be advised to test their drugs in a safe setting before taking them at work or while travelling. Anticholinergic, antihistamine, and sympathomimetic are three subcategories of medications.

Anticholinergic

Scopolamine-  Acting as a nonselective antimuscarinic by blocking input to the vestibular nuclei, it is now the most effective drug. It has a lower sedative effect than antihistamines. It is also offered as a transdermal patch At least four hours before travel, the patch should be put on the mastoid, and its effects will remain for 72 hours. Typical adverse effects include dry eyes and mouth, photosensitivity, impaired vision, vertigo, headache, and drowsiness. This medication is contraindicated for children under the age of 12 and should be taken with care in the elderly. Acute angle glaucoma, disorientation, contact dermatitis, and urine retention are uncommon adverse effects.

In recent research undertaken by NASA and the Naval Aerospace Medical Research Laboratory, intranasal scopolamine has been of special interest in addressing the considerable discomfort of space motion sickness in astronauts. It has been discovered that the nasal gel formulation of scopolamine has more quick absorption and commencement of action than its transdermal or oral equivalents, as well as a more predictable effectiveness profile and a more desirable side effect profile. No major cognitive or sedative effects have been identified in studies, which may provide a potential answer for both astronauts functioning in highly technological workplaces.

Antihistamines

Antagonists of the H1 receptor inhibit the firing of semicircular canal afferent neurons generated by the hypothalamic histaminergic system. Sadly, H1 antagonists are quite sedating. Studies have shown that the less sedating second-generation antihistamines are unsuccessful in the treatment of motion sickness, perhaps owing to peripheral rather than central receptor mediation.

Diphenhydramine- Antihistamine of the first generation with anticholinergic effects. Oral (over-the-counter) and injectable formulations are available. Sedation is prevalent. Also prevalent are dry mouth and eyes, impaired vision, and photosensitivity. Rarely do confusion and urine retention develop.

Cyclizine- Oral antihistamines of the first generation are accessible over the counter. It has shown comparable effectiveness to diphenhydramine, but with less sedation and a more direct effect on the stomach in the treatment of gastrointestinal problems. It is FDA-approved for use by adults and children older than 6 years.

Meclizine -  Oral antihistamines of the first generation are accessible over the counter. They are recommended for patients 12 and older, although they are quite sedating.

Cinnarizine - A first-generation antihistamine that treats motion sickness symptoms more effectively and with less drowsiness.

Promethazine - Antihistamine of the first generation with anticholinergic effects. It is available by prescription only in oral, rectal, and intramuscular formulations. Promethazine has also been researched in the context of intramuscular injections, which are routinely used to treat space motion sickness. However, research indicates that its negative effects may impede operational performance. Some negative effects of promethazine are effectively counteracted by combining it with coffee.

Sympathomimetic

Dopaminergic and noradrenergic pathways are stimulated by dextroamphetamine in conjunction with anticholinergics and antihistamines, demonstrating that dextroamphetamine has a synergistic effect. Dextroamphetamine and scopolamine are the most effective anti-motion sickness combo, according to studies, since they function via various pathways and their negative effects cancel one other out. Nonetheless, the potential for drug dependency must be considered. For motion sickness, sympathomimetic medications are mostly used during space trips.

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Patients who need to avoid sedation 

Due to the possible sedative effects of the drugs used to prevent motion sickness, it might be difficult for patients who must perform responsibilities such as piloting an aircraft or serving as crew to avoid motion sickness. Dimenhydrinate, for instance, may have very detrimental performance impacts.

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Therapies Not Recommended

Dopamine antagonists, such as metoclopramide, have not shown consistent success in treating motion sickness. Although metoclopramide is a powerful antiemetic and improves stomach emptying, studies have not shown its effectiveness in treating motion sickness. Ondansetron and other serotonin (5-HT3) receptor antagonists are strong antiemetics and reduce stomach tachyarrhythmia, but they are ineffective in preventing motion sickness.

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Drugs For Patients Who Are Pregnant

Women who are pregnant may be more susceptible to motion sickness. Medications used to treat morning sicknesses, such as meclizine and dimenhydrinate, are considered safe for use in motion sickness. The FDA defines them as pregnancy category B. Scopolamine and promethazine are Class C in pregnancy.

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References-

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Disclaimer- The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or position of M3 India.

About the author of this article: Dr Monish Raut is a practising super specialist from New Delhi.