Motion sickness is a common and complex syndrome that occurs in response to the real or perceived motion. Its presentation can be diverse, including the gastrointestinal, central nervous system, and autonomic symptoms. There is considerable individual variability in motion sickness susceptibility, as some individuals may suffer from minimal provocation and in others, it may be very difficult to elicit symptoms.
Motion sickness symptoms were first described by Hippocrates, who wrote, “sailing on the sea proves that motion disorders the body.” The main symptom of motion sickness, nausea, is derived from naus, the Greek word for ship (e.g., nautical).
Motion sickness occurs when there is a mismatch between actual versus expected sensory inputs. Although the exact neurobiological mechanism is unclear, many countermeasures have been developed to prevent and alleviate this condition.
Motion sickness is typically triggered by low-frequency lateral and vertical motion (example: air, sea, road transportation) or by virtual simulator motion (video games, virtual simulators). The sensory conflict and neural mismatch theory is the most widely accepted theory for explaining motion sickness. It describes the conflict that occurs between the visual, vestibular and somatosensory systems resulting from real or virtual motion. Afferents from the vestibular apparatus arrive at the vestibular nuclei of the brainstem, which also receives inputs from the visual and proprioceptive systems. Efferent projections then reach the temporoparietal cortex via the posterolateral thalamus, triggering autonomic reactions and the vomiting center. When there is a discrepancy between actual versus expected patterns of vestibular, visual, and kinesthetic inputs, it initiates the cascade of motion sickness symptoms.
Motion sickness is inducible in almost all people with a functioning vestibular apparatus and a sufficient provocative stimulus. Patients with total loss of labyrinthine function are immune to motion sickness.
The symptoms of motion sickness can be diverse, ranging from the most common, nausea and vomiting, too cold sweating, pallor, headache, drowsiness, yawning, loss of appetite and increased salivation. Typically, an inciting event or exposure to an unfamiliar motion precedes symptoms of motion sickness. The constellation of symptoms known as “sopite syndrome” refers to profound drowsiness and fatigue that can persist for hours to days following exposure. It may appear to untrained observers as apathy, boredom, irritability and personality changes.
Less commonly, severe symptoms may occur. These include the inability to walk, incapacitation, postural instability, intractable retching, and social isolation. The failure to diagnose the early and more mild symptoms of motion sickness may delay treatment.
Motion sickness is a clinical diagnosis made with a thorough history and physical. Generally, further workup through laboratory or radiographic testing is not necessary if a patient has a typical presentation or a previous history of motion sickness.
In a patient with an abrupt onset of motion sickness symptoms, workup for migraine headaches may be indicated, as they have shown to be closely associated. The prophylactic treatment of migraines may not only decrease headaches but can improve associated dizziness and motion sickness symptoms.
It is crucial to identify the life-threatening causes for motion sickness like basilar artery occlusion. Sometimes the initial presenting symptom for basilar artery occlusion is dizziness and motion sickness. Usually, these patients have other associated symptoms which are sudden in onset like diplopia, dysarthria, dysphagia and drop attacks. When suspecting basilar artery occlusion, it is vital to do CT angiography to rule out basilar artery occlusion. Once it is ruled out, then one can look for benign paroxysmal positional vertigo, vestibular migraine, vestibular neuritis, etc.
Behavioral countermeasures against motion sickness are among the most effective treatments.
Habituation is the most effective long-term countermeasure. It lacks the adverse effects of pharmacotherapy, such as drowsiness and blurred vision. Unfortunately, this time-consuming approach may last many weeks, as evidenced by the military-run motion sickness desensitization programs created to treat pilots in which anti-motion sickness medications are contraindicated. These programs are designed for long-term success, with rates exceeding 85%. In the general population, with continuous exposure, the symptoms of motion sickness generally resolve within 24 to 72 hours. However, if the intervals between exposure are greater than one week, long-term habituation may not be achieved.
Alternative treatments include the use of ginger, which acts as an antagonist at the 5-HT3 receptor that plays a role in vomiting. Acupressure bands at the P6 or Neiguan point on the anterior wrist have shown benefit in the treatment of nausea and vomiting in a limited number of trials. However, more data is needed.
Medications for the treatment of motion sickness are only partially effective and may have unwanted side effects. They are most effective when used prophylactically or at the early onset of symptoms. Patients should be encouraged to first trial the medications first in a safe environment before using during work or travel. Medications can subdivide into categories: anticholinergic, antihistamine and sympathomimetic.
H1 receptor antagonists decrease the firing of afferent nerves of the semicircular canals that are triggered by the histaminergic system in the hypothalamus. Unfortunately, H1 antagonists are highly sedating. Studies have determined the less sedating second-generation antihistamines to be ineffective in treating motion sickness, likely due to mediation via peripheral versus central receptors.
Therapies not recommended
Medications for pregnant patients
Pregnant women may have increased susceptibility to motion sickness. Medications used for morning sickness are felt to be safe for use in motion sickness, including meclizine and dimenhydrinate. The FDA classifies these as category B in pregnancy. Scopolamine and promethazine are Class C in pregnancy.
Individuals with a history of motion sickness will have a high likelihood of recurrence in the presence of a provocative stimulus unless able to achieve habituation. Due to the wide variation of symptom severity, patients and providers should weigh the risks and benefits of pharmacotherapy on an individual basis.
The majority of individuals with motion sickness have mild to moderate symptoms that are self-limited. Once the triggering motion ceases, symptoms often resolve entirely within 24 hours. The minority of patients whose condition progresses to extreme nausea and vomiting may result in dehydration, electrolyte disturbances or esophageal tears.
Prevention of motion sickness is more efficacious than treatment; therefore identification and/or avoidance of triggers are key. Patients must employ behavioral countermeasures including preparation, habituation, and possibly pharmacotherapy to be able to minimize their symptoms effectively. For patients who require pharmacotherapy, emphasis should be on side effects including sedation and cognitive impairment to reduce potential risks.
Motion sickness is a common condition that practitioners should be prepared to evaluate and treat. Prevention of symptoms is more effective than treatment; therefore the primary care provider and nurse practitioner should provide education and emphasize behavioral countermeasures to minimize sensory conflict. When indicated, many pharmacologic options are available, and healthcare workers should carefully weigh the risk: benefit ratio to minimize adverse effects. Clinicians must also be aware of the “red flag” signs of vestibular and neurologic pathology, as symptoms may be confused with motion sickness.
Aerospace programs, aiming to treat symptoms in astronauts without compromising alertness and cognitive function, have led the future of motion sickness treatment. Intranasal scopolamine offers promise for future use but it not yet available commercially.
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