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Micturition Syncope

Micturition Syncope (context Dependent Category)

A micturition syncope, sometimes also called post-micturition syncope, describes the phenomenon of somebody fainting during or shortly after micturition. The syncope occurs due to vegetative responses triggered by stimulation of the nervus vagus.


MS are syncopes occurring during or shortly after urination. As such, prodromal signs like light-headedness or dizziness may be experienced while urinating. Some patients also report feeling weak or nauseated, becoming pale or starting to sweat. In MS, these symptoms are followed by a brief loss of consciousness.

Additional symptoms may be present and may hint at a more severe underlying disease. It is thus of utmost importance to obtain the complete medical history of the patient.

Drop Attacks
  • It is thought that the reticular activating system controls consciousness and that ischemia of this region may lead to drop attacks or syncope. Other vascular diseases of cerebral arteries may also present with syncope when there is sudden ischemia.[ncbi.nlm.nih.gov]
  • Drop attacks involve sudden falls without loss of consciousness or warning and with immediate recovery.[aafp.org]
  • Differential diagnosis of Blackouts • Syncope • Epilepsy • Psychogenic non-epileptic seizures •Cataplexy  Drop attack • Transient CSF obstruction • Transient ischaemic attack - anterior and posterior circulation • Panic attack, • Falls / trauma • Hypoglycaemia[slideshare.net]


A tentative diagnosis can usually be provided upon obtaining the anamnesis of the patient. Contrary to other diseases that may present possible differential diagnoses, MS are not associated with major risks for human health. Thus, the aim of a medical workup is to exclude other and more severe pathological conditions that would trigger the same symptoms, e.g. cardiac arrhythmia, distinct types of cardiomyopathy, aortic stenosis, hypotension and hypovolemia.

Thorough auscultation, lying and standing blood pressures, tilt-table testing as well as echocardiography and imaging techniques may be of help to identify the cause of the observed syncopes [10].


Patients suffering from MS should take the appropriate safety measures, particularly if one can identify certain triggers of syncopes. It is recommended to keep the door to the bathroom open and to remove any sharp or otherwise dangerous objects from where syncopes may occur. If syncopes are frequently observed after standing up quickly or standing for prolonged periods of time, thus these habits should be changed or avoided. Similarly, other triggers such as excess warmth and alcohol should be avoided.

If the patient is taking any hypotensive medication - either in form of antihypertensive drugs or as pharmaceuticals with hypotensive side effects - it should be carefully considered if this medication may be replaced or stopped. This particularly applies to alpha-sympatholytic agents and antidepressants.

Fludrocortisone has been used to stabilize blood pressure, but there are no reliable data regarding its effects in patients suffering from MS. It has also been suggested to administer selective serotonin reuptake inhibitors to avoid syncopes, but their effect has not been proven yet. Indeed, selective serotonin reuptake inhibitors may even further decrease blood pressure. Beta-sympatholytic drugs had been proposed as possible treatment for patients suffering from syncopes, but no significant effects could be detected in recent clinical trials [11]. Noteworthy, patients suffering from spinal cord injuries have been injected with botulinum A toxin into the musculus detrusor [12].

Because there is no medication therapy that guarantees success, patients should be advised regarding physical counter measures that may help reduce the frequency of MS. In this line, arm tensing and leg crossing have been proposed and proven effective [13].

Due to the fact that vasovagal syncopes provoke a decrease of the heart rate, cardiac pacing may result an attractive treatment option. Different studies have been conducted in order to evaluate if patients suffering from syncopes benefit from cardiac pacing, but could not confirm this hypothesis [14].


MS consist in short episodes of loss of consciousness. Although the vegetative nervous system, the heart's activity as well as brain perfusion are affected by the chain of events leading to MS, they do not pose a major threat for human health.

The biggest risk associated with MS is the risk of falling and suffering from lacerations, contusions or even fractures. The fact that older people that may suffer from comorbidities are more commonly affected by MS increases the risk of severe traumas. It has been estimated that one in three patients suffering from syncopes has experienced some kind of trauma due to fainting and falling.

In general, vasovagal syncopes may also occur while driving a car or while being otherwise occupied with potentially dangerous activities. Due to the nature of MS, this kind of risk is not typically associated with this kind of syncopes.

Besides health risks attributed to MS, syncopes may diminish the quality of life of the affected person due to social marginalization, e.g. when hiring someone for a job.

Drug therapy may lessen the frequency of MS but are not always effective.


Bladder filling and micturition are physiologically associated with changes in blood pressure and heart rate that are, in turn, triggered by activation of sympathetic and parasympathetic branches. The sympathetic tone increases with bladder filling and peaks at the beginning of micturition, thus provoking an increase in blood pressure and heart rate. During micturition, the parasympathetic tone augments and provokes a decrease of blood pressure and heart rate.

It has been suggested that MS occur due to hypotension and bradycardia that are, in turn, triggered by a stimulation of the vagus nerve during urination [1] [2]. This kind of vasovagal response may be provoked by dysuria or other conditions requiring additional efforts in order to urinate. A case description has been published that associated intermittent catheterisation to hypotension and syncopes in a tetraplegic patient, a condition possibly mediated by a hyperreflective bladder [3]. Furthermore, patients suffering from multiple system atrophy are more prone to MS, because they tend to become hypotensive during urination [4].

Since MS occur more frequently in patients that have recently awoken from sleep and got up to urinate, postural hypotension may also play a certain role in MS etiology. Similarly, quick or prolonged standing may lead to MS. Indeed, it has been shown that orthostatic stress causes blood pooling and plasma loss due to increased hydrostatic pressure that amounts to a total volume of more than one liter [5].

Moreover, any drugs provoking bradycardia and hypotension may contribute to the pathological condition triggering MS. The same effects are mediated by excessive warmth and alcohol, which may therefore provoke hypotension and subsequent MS, too.

The aforementioned triggers of MS may be reinforced when occurring in a combined form. They may additionally be potentiated by confined spaces, fasting, fatigue and emotional stressors.

Even though there is a certain consensus in the cardiovascular conditions that ultimately cause MS, the exact causes for these conditions remain poorly understood. Presumably, other factors are involved in the etiology of MS and leave certain patients more susceptible to this kind of syncopes than others. This hypothesis is supported by the fact that distinct diseases leave patients more susceptible to MS, as has been described above.


Vasovagal syncopes are frequently observed in young and old patients (incidence peaks at about 15 years of age and at about 70 years of age), but MS does only account for less than 10% of all cases of syncopes [6]. Here, the term "vasovagal" refers to a reduction of blood pressure and heart rate due to vagal stimuli [7] [8].

MS most commonly affects men aged 30 to 50 years and thus does not match the trends observed in studies regarding the epidemiology of vasovagal syncopes in general. The majority of MS occurs at night, in people that wake up and stand up to urinate.

More than half of the patients suffering MS do also experience other types of syncopes [6]. This fact further complicates analysis and comparison of different studies.

Sex distribution
Age distribution


MS are vasovagal syncopes, i.e. they are ultimately caused by cardiovascular conditions that, in turn, are provoked by an increasing parasympathetic tone and a decreasing sympathetic tone. These vegetative responses are caused by an as yet unknown trigger that activates the nucleus of the solitary tract, the main visceral sensory nucleus. This nucleus does receive input from afferent vagus nerve fibers.

In detail, the vegetative responses mediated by activation of the nucleus tractus solitarii are:

  • Negative chronotropy and negative inotropy. A decrease of the heart rate as well as a reduction of myocardial contractility both contribute to a reduction of the cardiac output. Presumably, this effect is mediated by an increased parasympathetic tone.
  • Vasodilation. Vasodilation provokes a considerable reduction of blood pressure. Values as low as 80 to 20 have been reported. For young people suffering from syncopes, it has been shown that the reduction in blood pressure is equally caused by arterial and venous vasodilation [9]. Due to the vegetative innervation of blood vessels, this effect is most probably mediated by a decreased sympathetic tone.

Both the cardioinhibitory response and the vasodepressor response may contribute to MS. Patients will usually suffer from both rather than from an isolated cardioinhibitory or vasodepressor effect. The Bezold-Jarisch reflex may serve as an explanation for this chain of physiological adjustments.

Consequently, cerebral blood flow diminishes. MS itself is a mere symptom of reduced cerebral perfusion that results in the patient losing consciousness.


Preventive measures may be taken as soon as syncopes are diagnosed and other, more severe diseases have been ruled out. Prevention mainly consists in avoiding possible triggers. Patients may be able to identify certain triggers that are particularly important for them. In general, patients should be given the following advice:

  • Avoid prolonged standing and standing up quickly.
  • Urinate while sitting down.
  • Drink sufficient water, but minimize alcohol intake.
  • Avoid excess warmth.
  • Do not fast for prolonged periods of time.
  • Make sure to get enough sleep.

Additionally, physical measures may be taken to avoid syncopes, e.g. arm tensing and leg crossing [12].


Micturition syncopes (MS) are characterized by loss of consciousness during or shortly after urinating. They are caused by a reduction of cerebral perfusion that, in turn, is provoked by decreases of blood pressure and heart rate.

MS are vasovagal syncopes, i.e. vagal stimuli conducted to visceral sensory nuclei in the brain do trigger the above mentioned symptoms. The exact triggers still remain unknown. Dysuria and other problems requiring additional efforts to urinate may contribute to MS as well as certain diseases, hypotensive drugs, alcohol, excess warmth and other factors.

Medication therapy of MS is worth a try, but does not guarantee success. Thus, if a patient suffering from MS is able to identify certain triggers, he or she should avoid these triggers as far as possible. The patient should also take measures to prevent severe traumas resulting from falling during a syncope. Indeed, the intrinsic risks of MS to human health due to blood pressure or heart rate issues are low, but consequences arising from falling down when experiencing a MS can be quite severe.

Patient Information

While the term syncope refers to a loss of consciousness in a general way, a micturition syncope (MS) is characterized by syncopes occurring while or shortly after urinating. Patients suffering from MS may become pale, start to sweat, feel weak, and experience dizziness and light-headedness before fainting during or after micturition.

Micturition activates the vagus nerve, a nerve whose main function is to regulate several internal organs such as the heart, the gastrointestinal tract and the bladder. Vagus nerve signals are conducted to the brain and trigger the reduction of blood pressure and heart rate. These events precede a decrease in cerebral blood flow and ultimately lead to a loss of consciousness that is related to urination, a MS. This whole chain of events is called a vasovagal response, because the cardiovascular system reacts to stimuli originating from the vagus nerve.

Additional triggers such as orthostatic stress due to prolonged standing or standing up quickly, excess warmth, consumption of alcohol or the intake of drugs causing hypotension may be necessary to trigger a MS. This, in turn, means that a patient experiencing MS may reduce the frequency of syncopes by avoiding these triggers. With regard to drugs causing hypotension, a physician has to evaluate whether the patient may benefit from replacing or stopping the respective medication. Otherwise, therapeutic options are limited.

The major risk associated with MS is that of traumas that may be endured when falling while experiencing a syncope. Thus, it is recommended to take preventive measures such as removing sharp or otherwise dangerous objects from the bathroom, padding its floor and keeping the door to the bathroom unlocked



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Last updated: 2018-06-22 04:48