Differentials
Neurally mediated (vasovagal) syncope
SIGNS / SYMPTOMS
Premonitory symptoms such as sweating and nausea/gastric discomfort are typical of neurally mediated (vasovagal) syncope, but do not occur in patients with chronic autonomic failure.
Symptoms of neurally mediated syncope are intermittent and frequently occur with specific triggers (e.g., blood drawing, prolonged standing, emotional upset). In between episodes, blood pressure responses are normal, and symptoms are not related to eating or physical exercise.
INVESTIGATIONS
In the tilt-table test, the blood pressure is initially maintained until, after a variable period, it falls abruptly, often in association with a drop in heart rate, which can range from asystole to only a few milliseconds of slowing. In contrast, in OH the fall in blood pressure occurs immediately upon head-up tilt, and is usually progressive.
The autonomic response to the Valsalva manoeuvre is normal; in contrast, in autonomic failure there is lack of blood pressure overshoot after release of the strain.
Noradrenaline (norepinephrine) levels increase appropriately on standing, but fail to continue increasing at the time of syncope.
Vertigo
SIGNS / SYMPTOMS
Vertigo is the result of vestibular or cerebellar pathology, but it may be confused with the dizziness or light-headedness of orthostatic hypotension.
INVESTIGATIONS
Neurological examination reveals cerebellar ataxia or nystagmus. Vestibular testing with electronystagmography shows abnormal responses.
Non-specific falls in older people
SIGNS / SYMPTOMS
Gait imbalance and falls are common in older people and may be the result of impaired postural reflexes, reduced visual acuity, or orthopaedic problems, and may be confused with orthostatic hypotension. Non-specific falls can be assessed by physical examination, including a full neurological examination. When questioned, patients with basal ganglia dysfunction may describe the sensation of being inebriated when standing due to impairment in balance.
INVESTIGATIONS
Neurological examination showing gait imbalance or abnormal postural reflexes.
Psychogenic syncope (pseudo-syncope)
SIGNS / SYMPTOMS
Periods of unresponsiveness due to psychiatric disorders can easily be confused with syncope. A psychiatric evaluation is required to determine the cause.
A high attack frequency and delayed recovery, atypical triggers, and lack of prodrome are more typical.
INVESTIGATIONS
Unresponsiveness during a tilt-table test with a documented lack of hypotension or bradycardia is very suggestive of psychogenic syncope. Unresponsiveness without seizure activity or flattening of the electroencephalogram (EEG) during EEG monitoring is virtually diagnostic.
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