Multiple sclerosis (MS) is a chronic neurological disorder that affects the central nervous system, causing inflammation and damage to the protective layer of nerve fibers called myelin. MS can cause a variety of symptoms, such as vision problems, muscle weakness, fatigue, and cognitive impairment. MS is a complex and unpredictable disease that can vary in severity and progression among different individuals.
Vasovagal syncope (VVS) is a common type of fainting that occurs when the body overreacts to certain triggers, such as emotional stress, pain, heat, or the sight of blood. VVS is caused by a sudden drop in blood pressure and heart rate, which reduces the blood flow to the brain and leads to a temporary loss of consciousness. VVS is usually harmless and does not require any specific treatment, but it can cause injuries or accidents if it happens unexpectedly.
Both MS and VVS involve the dysfunction of the autonomic nervous system, which regulates involuntary bodily functions such as blood pressure, heart rate, temperature, and digestion. However, the relationship between these two conditions is not well understood. Some studies have suggested that MS patients may have a higher risk of developing VVS or other forms of dysautonomia, while others have found no significant association. In this article, we will review the current evidence on the possible link between MS and VVS, and discuss the implications for diagnosis and management.
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How common is VVS in MS patients?
The prevalence of VVS in MS patients is difficult to estimate, as there are no standardized criteria or methods for diagnosing VVS in this population. Moreover, VVS may be confused with other causes of fainting or dizziness in MS patients, such as orthostatic hypotension, vestibular dysfunction, or medication side effects. Therefore, the reported rates of VVS in MS patients vary widely among different studies, ranging from 0% to 40%
One of the largest studies on this topic was conducted by Adamec et al., who analyzed the autonomic function of 70 MS patients and 30 healthy controls using various tests, such as heart rate variability (HRV), tilt table test (TTT), and quantitative sudomotor axon reflex test (QSART) They found that 30% of MS patients had VVS, compared to 3.3% of controls. They also found that VVS was more common in patients with progressive MS (40%) than in those with relapsing-remitting MS (20%). Furthermore, they observed that VVS was associated with longer disease duration, higher disability score, lower HRV, and higher sudomotor index.
Another large study by Damla et al. examined the HRV of 51 newly diagnosed RRMS patients and 44 healthy controls using 24-hour Holter monitoring They found that RRMS patients had lower HRV than controls, indicating impaired autonomic regulation. However, they did not find any correlation between HRV and clinical parameters such as disease duration, disability score, or lesion location. They also did not perform any other tests to confirm the diagnosis of VVS in their patients.
Other smaller studies have reported conflicting results on the prevalence and characteristics of VVS in MS patients. For example, some studies have found no difference in the frequency or severity of VVS between MS patients and controls, while others have found higher rates of VVS in MS patients than in controls. Some studies have also suggested that VVS may be related to specific lesion sites in the brainstem or spinal cord, while others have found no such association.
What are the possible mechanisms underlying VVS in MS patients?
The exact mechanisms that cause VVS in MS patients are not fully understood. However, several hypotheses have been proposed based on the available evidence.
One hypothesis is that MS lesions disrupt the neural pathways that regulate the autonomic nervous system, leading to abnormal responses to various stimuli. For instance, lesions in the brainstem may impair the baroreflex mechanism that adjusts blood pressure and heart rate according to changes in posture or blood volume. Lesions in the spinal cord may affect the sympathetic or parasympathetic nerves that innervate the heart and blood vessels. Lesions in other brain regions may alter the emotional or cognitive processing of stressful situations that trigger VVS.
Another hypothesis is that MS causes chronic inflammation and oxidative stress that damage the endothelial cells that line the blood vessels. This may impair the production or release of nitric oxide (NO), a vasodilator that helps maintain normal blood pressure and blood flow. Reduced NO levels may increase vascular resistance and decrease cerebral perfusion during episodes of VVS.
A third hypothesis is that MS affects the hormonal balance that influences the autonomic nervous system. For example, MS may alter the levels of cortisol, a stress hormone that modulates blood pressure and heart rate. MS may also affect the levels of sex hormones, such as estrogen and testosterone, that have various effects on the cardiovascular system. Hormonal changes may affect the sensitivity or reactivity of the autonomic nervous system to different stimuli.
How can VVS be diagnosed and treated in MS patients?
The diagnosis of VVS in MS patients can be challenging, as there are no specific tests or criteria that can confirm or exclude VVS in this population. Moreover, VVS may mimic or overlap with other causes of fainting or dizziness in MS patients, such as orthostatic hypotension, vestibular dysfunction, or medication side effects. Therefore, a thorough medical history and physical examination are essential to identify the possible triggers and features of VVS in MS patients. Additionally, some tests may be helpful to assess the autonomic function and rule out other conditions, such as:
- Electrocardiogram (ECG) to detect any cardiac arrhythmias or conduction abnormalities
- Echocardiogram to evaluate the structure and function of the heart
- Blood tests to check for anemia, electrolyte imbalance, or infection
- Tilt table test (TTT) to provoke VVS by changing the body position from lying to standing
- Heart rate variability (HRV) to measure the fluctuations in heart rate over time
- Quantitative sudomotor axon reflex test (QSART) to evaluate the sweat response of the skin
The treatment of VVS in MS patients depends on the frequency and severity of the episodes, as well as the presence of any underlying conditions or risk factors. In general, the treatment goals are to prevent or reduce the occurrence of VVS episodes, avoid injuries or complications from fainting, and improve the quality of life of MS patients. The treatment options include:
- Lifestyle modifications, such as avoiding triggers, staying hydrated, wearing compression stockings, elevating the head of the bed, and performing physical exercises
- Behavioral techniques, such as tensing the muscles or crossing the legs during an episode, or lying down and elevating the legs if feeling faint
- Medications, such as beta blockers, fludrocortisone, midodrine, or selective serotonin reuptake inhibitors (SSRIs), to increase blood pressure and heart rate
- Pacemaker implantation, in rare cases where medications are ineffective or contraindicated, to regulate the heart rhythm
Conclusion
VVS is a common type of fainting that occurs when the body overreacts to certain triggers, causing a sudden drop in blood pressure and heart rate. MS is a chronic neurological disorder that affects the central nervous system, causing inflammation and damage to the myelin sheath that covers nerve fibers. Both conditions involve the dysfunction of the autonomic nervous system, which regulates involuntary bodily functions.
The relationship between MS and VVS is not well understood. Some studies have suggested that MS patients may have a higher risk of developing VVS or other forms of dysautonomia, while others have found no significant association. The possible mechanisms that cause VVS in MS patients may include neural damage, vascular impairment, or hormonal imbalance.
The diagnosis and treatment of VVS in MS patients can be challenging, as there are no specific tests or criteria that can confirm or exclude VVS in this population. Moreover, VVS may mimic or overlap with other causes of fainting or dizziness in MS patients. Therefore, a thorough medical history and physical examination are essential to identify the possible triggers and features of VVS in MS patients. Additionally, some tests may be helpful to assess the autonomic function and rule out other conditions. The treatment options include lifestyle modifications, behavioral techniques, medications, and pacemaker implantation.
VVS is usually harmless and does not require any specific treatment. However, it can cause injuries or accidents if it happens unexpectedly. Therefore, MS patients who experience VVS should consult their doctor for proper diagnosis and management.
