There is no definitive test for autonomic dysfunction. The diagnosis is made by recognizing from the history a constellation of any number of the typical symptoms occurring during typical circumstances and made worse in the presence of additive factors. Before a diagnosis is made, the history should be consistent with way vasovagal dysfunction occurs as just described and all other causes should be ruled out as best as possible.
The history is often typical; one has a longstanding history of feeling dizzy, getting blackout or tunnel vision and sometimes fainting upon standing, sometimes palpitations are common with position changes, sometimes one has excessive sweating, chronic fatigue, frequent episodes of nausea and migraine headaches. Triggers include postural changes (standing up), excessive heat, a claustrophobic situation, hypoglycemia, pain, or an objectionable sight such as blood. The most common history is that of a person fainting moments after getting up to a standing position. Often this is first thing in the morning and often times right after urination or getting up from the toilet. It’s usually before breakfast. Often times its after lying and watching TV for a long time or after standing from sitting while doing homework a long time.
Other common scenarios include after coming out of a hot shower or while having one’s hair brushed, while standing for a long time in a line, or in band practice while standing on a hot pavement, while standing in the lunch line waiting for food, while standing in a crowded, hot, church. Also, following an episode of extreme pain or following the sight of blood or other objectionable sight.
History of Syncopal Episodes
When fainting is involved, the history should include prodromal symptoms (symptoms that precede the loss of consciousness. Light-headedness, spots before eyes, tunnel vision, black-out of vision, hearing changes where those talking around sound distant or other change, nausea are all common feelings just before fainting. It’s rare for a person who had a vasovagal event to suddenly loss consciousness without any symptoms beforehand. The history should not include the feeling of palpitations or a racing heart as the first sensation before lightheadedness and fainting. Fainting should not occur while in the midst of heavy exertion but it may occur during the recovery from exertion. The history should also not include any seizure-like activity before or in the early part of loss of consciousness. However, seizure-like activity is very often seen when one is recovering from a vasovagal syncopal event. Unconsciousness should be very brief with vasovagal syncope; on the order of 30 to 60 seconds.
Family history should also be carefully evaluated. This is mainly to increase suspicion of other more serious causes of any symptoms. Having said that, those who have autonomic dysfunction often have a parent who also had similar episodes when they were the same age.
Typically, there are no unusual physical exam findings in a person with autonomic dysfunction. Orthostatic blood pressure measures in the lying, sitting and standing position almost always reveals a nearly constant blood pressure but may reveal a heart rate rise that is greater than 20 faster than the lying position (orthostatic changes). Also, very often the evaluation is taking place on a day different from the most recent event and so any ’additive factors’ glycemic state, hydration status and amount of sleep) are no longer present and no abnormality is found.
Studies: An ECG and echocardiogram swill likely be performed to rule-out structural and electrophysiologic causes of many of the symptoms. If there is any suggestion of seizure as a cause, a neurology referral should be sought and an EEG may be in order. If there is any suggestion that an arrhythmia is the cause, event recorders, and a Holter monitor may be ordered. Tilt-table test is rarely performed in pediatrics as the sensitivity and specificity in young people are very low as shows little information over the orthostatic pressure measures that should be done with vital signs.
In search of the ’Ker-plunk’
Depending on the severity of symptoms or grade of dysfunction, blood and urine is often tested. Those with severe dysfunction may undergo a very large battery of tests. The battery of lab tests I perform and the sequence of testing I often employ can be found in the supplement in the back of this piece.
Various signs and lab studies can differentiate POTS into Neuropathic POTS with loss of sweating in the feet and impaired NE release in response to orthostatic stress. Hyperadrenergic POTS with increased central sympathetic drive with standing NE levels of >600 pg/ml, fluctuating blood pressure with hypertensive responses to standing. High flow, low-flow and normal-flow POTS.