The cornerstone of evaluation is a detailed history and physical examination. When do syncopal or near-syncopal episodes occur, and when did they begin? How often do they occur? Is there a pattern to the events or any known precipitating factors? What are episodes like for the patient, and how do they appear to bystanders? What other organ systems are involved? Other than syncope, what symptom bothers the patient most? A careful and concise history and physical exam (which must include a concise neurologic examination) will have a far greater diagnostic yield than the routine ordering of multiple tests. Laboratory examinations should be obtained in a careful and directed manner, based upon history and physical findings, to confirm one's clinical impressions.
It is far beyond the scope of this chapter to review every autonomic disorder and the various tests used in evaluation. The interested reader is directed to several excellent texts on the subject (80,87-90). It is important to note that any drugs the patient is taking that could produce hypotension should be identified (see Table 6). This includes not only pharmaceuticals, but over-the-counter medications and herbal remedies as well. Sadly, in the modern era, when a young person presents with symptoms of autonomic dysfunction, the potential use of illicit drugs or alcohol should be considered. In women, symptoms may vary with the menstrual cycle, or an otherwise mild tendency toward autonomic dysfunction may be exacerbated by the onset of menopause.
Since the autonomic areas of the brain are not accessible to direct measurement, one must measure the responses of various organ systems to various physiologic or pharmacologic challenges. In addition, recent advances have allowed for the determination of serum urine and cerebrospinal fluid levels of some autonomic neuromodulators and neurotransmitters. Foremost, however, is the determination of the blood pressure and heart rate response to positional change, with measurements taken while supine, sitting, and standing. The exact change in pressure considered to be significant is still under discussion, but is usually believed to be 20-30 mm/Hg systolic and 10-15 mm/ Hg diastolic. Remember that standing blood pressure should be measured with the arm extended horizontally (to avoid the possible hydrostatic effects of the fluid column of the arm). Since the body's responses to active standing differ from those of passive tilting, we also frequently perform tilt-table testing on these patients (91). A number of other autonomic tests are also available, and are quite useful in selected patients (87-90).
We have found it useful to distinguish between these broad response patterns as outlined in Fig. 3. The first of these is the classic neurocardiogenic (or vasovagal) response. This is characterized by a sudden fall in blood pressure often followed by a fall in heart rate. The second pattern is referred to as dysautonomic and demonstrates a gradual but progressive decline in blood pressure to hypotensive levels leading to loss of consciousness. The third pattern is characteristic of POTS (83). Initially, we defined this group as exhibiting an increase of at least 30 BPM (or a maximum of 120 BPM) within the first 10 min of passive upright tilt, which is usually not associated with profound hypotension. Recently, we have realized that there are probably subgroups within the POTS population, and we are working to better categorize these.
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