Distinguishing between orthostatic intolerance, POTS, and vasovagal syncope in children

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Symptoms of dizziness, lightheadedness, syncope, nausea, fatigue, and headaches are quite common in children and adolescents. Pediatricians often face the challenge of using symptoms and more objective findings together to categorize patients. Although some believe this group of symptoms represents a spectrum of disease, there appears to be important differences in both pathophysiology and clinical presentation. Another issue has been the use of adult criteria for heart rate changes during tilt table testing. This may be problematic because of the normal age-related changes seen in heart rate (HR) and HR response throughout the pediatric age range.

In this issue of The Journal, two groups approach these issues from different perspectives. Singer et al report on normal results during 70-degree head-up tilt testing. These results confirm that adult criteria are not appropriate for children. They propose that orthostatic intolerance (OI) be defined by symptoms, such as light headedness, that occur frequently when assuming an upright position and an orthostatic HR increment ≥ 40 beats per minute (bpm) within 5 minutes of head-up tilt. Postural orthostatic tachycardia syndrome (POTS) should include the criteria for OI and an absolute orthostatic HR ≥ 130 bpm (age 15 and younger) or ≥ 120 bpm (age 14 years and above) within 5 minutes of head-up tilt.

Zhang et al evaluated whether patients with POTS and vasovagal syncope (VVS) had different plasma concentrations of hydrogen sulfide, which is an endogenous gasotransmitter that is produced by vascular smooth muscle cells and endothelial cells. It appears to contribute to endothelium dependent vasodilation. They found that plasma levels of hydrogen sulfide were increased in the groups with POTS and VVS compared with controls, and that the plasma level of hydrogen sulfide had both high sensitivity and specificity to differentiate between POTS and VVS.

These studies further refine our knowledge of the area related to adolescent autonomic dysfunction and provide new approaches to clinical diagnosis. These studies emphasize that, ultimately, it will require a combination of symptoms, evaluation of heart rate, and laboratory tests to reach a definitive diagnosis.

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