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POTS Subtype: Does It Really Matter?

POTS is a syndrome that has multiple causes in different people.  One of our goals, as researchers trying to understand POTS, has been to try to better characterize POTS into subgroups (or “endophenotypes”).  The idea is that sub-groups of patients with POTS with more similar features may be more likely to have a common underlying cause. 

There are different mechanisms or abnormalities that we will often discuss as broad subtypes of POTS.  These include terms such as:

  • Hyperadrenergic POTS
  • Neuropathic POTS
  • Hypovolemic POTS
  • Mast Cell Activation Disorder

These terms are not really describing unique sub-types of POTS.  Instead, they are describing features that have been seen in some patients with POTS.

Characterizing POTS

What may be more valuable than the sub-type label is to “characterize the POTS”.  In the Vanderbilt Autonomic Dysfunction Center, this is done with tests that may include:

  • Autonomic Function (Reflex) Testing
  • Heart rate and blood pressure response to upright posture
  • Upright norepinephrine blood levels
  • QSART (sweat) testing
  • Blood volume measurement
  • Exercise testing

Knowledge of the results of these tests might yield information that helps provide some initial guidance for a therapeutic strategy.

Problem with POTS Subtype Labels #1: Same Name, Different Meanings

Most physicians that treat POTS use terms like “hyperadrenergic POTS” and “neuropathic POTS”.  However, one problem is that different physicians may mean different things when they use the same term.  For example, the term “hyperadrenergic POTS” may mean high norepinephrine levels to one doctor, it may mean really high norepinephrine levels without any other explanation for it (e.g. no hypovolemia), or it may mean that blood pressure goes up with standing.  In this case, the shorthand label may not just be unhelpful, but could actually cause confusion as different doctors may not understand why the label was used and think that it means something else.

Problem with POTS Subtype Labels #2: Labels not Mutually Exclusive

Another problem with these labels is that they are not mutually exclusive.  Some studies have labeled patients with “Hyperadrenergic POTS” if the patient’s upright plasma norepinephrine level is >600 pg/ml.  Other studies label patients with “Neuropathic POTS” if the QSART sweat test is abnormal.  Someone in the first study might say “I have hyperadrenergic POTS”, while the person in the second study might say “I have neuropathic POTS”.  The truth is that at least some (if not many) of those patients will have both abnormalities.   Often, these terms are not used to describe mutually exclusive subtypes, but to describe specific findings.

The Way Forward…

Our approach is NOT to focus on labels for POTS subtypes.  Rather, we prefer to characterize the POTS and address the individual findings as appropriate.