Objective:

To explore the clinical phenotypes and autonomic testing results of individuals with postural tachycardia syndrome (POTS) and orthostatic intolerance without tachycardia (OIwoT).

Background:

POTS is a debilitating form of dysautonomia associated with multisystem symptoms, including lightheadedness, tachycardia, nausea, constipation or diarrhea, difficulty concentrating, activity intolerance, and abnormal sweating, among others. Individuals with OIwoT also report similar autonomic complaints. There is limited data exploring how clinical phenotypes and objective testing differ between individuals with POTS and OIwoT.

Design/Methods:

This is a single-site, observational cohort study of adults who presented to an academic autonomic laboratory and met laboratory diagnostic criteria for POTS or had OIwoT. Exclusion criteria included: age <19 or >65, meeting laboratory criteria for orthostatic hypotension and medications that could affect testing. The Composite Autonomic Symptom Score-31 (COMPASS-31) total score and subscores were used to evaluate patient-reported autonomic symptoms. Participants were classified into two phenotypes based on laboratory testing: 1) hyperadrenergic phenotype if standing norepinephrine was >600 pg/mL and/or >3 times the supine norepinephrine level, and 2) neuropathic phenotype with Composite Autonomic Scoring Scale (CASS) score ≥2.  

Results:

This analysis included 389 individuals with POTS (mean age 32 years, 91% female) and 287 with OIwoT (mean age 36 years, 88% female). Median COMPASS-31 total score and domain subscores did not differ between POTS and OIwoT. The hyperadrenergic phenotype was more frequent in individuals with POTS (N=162 (74%) vs. N=114 (64%), p=0.02), whereas the frequency of the neuropathic phenotype did not differ between POTS and OIwoT.

Conclusions:

People with POTS and OIwoT have similar autonomic symptom severity and findings on the autonomic reflex screen, while high central sympathetic drive and/or an excessive sympathetic response to standing are more common in POTS compared to OIwoT. Further studies are needed to confirm these findings and their impact on diagnosis and management.