2023 American Academy of Neurology Abstract Website

Objective:

To compare postural tachycardia syndrome (POTS) with hypocapnic cerebral hypoperfusion (HYCH).

Background:

Several chronic orthostatic intolerance syndromes are associated with hypocapnia-driven cerebral hypoperfusion. Common syndromes are POTS where orthostatic tachycardia is present, and HYCH, where orthostatic tachycardia is absent.

Design/Methods:

This retrospective study evaluated consecutive patients with POTS and HYCH. Analyzed data included surveys (autonomic and sensory), autonomic (Valsalva maneuver, deep breathing, sudomotor and tilt tests), cerebrovascular (cerebral blood flow velocity (CBFv) monitoring in the middle cerebral artery), respiratory (capnography), neuropathic (skin biopsies for assessment of small fibers) testing and metabolic/inflammatory/autoimmune markers.

Results:

Eighty-one POTS and seventy-two HYCH patients were evaluated and they were compared to 25 healthy controls. POTS and HYCH patients had similar ages, gender, disease duration, and survey scores. Orthostatic CBFv was reduced in HYCH (-22.1±9.4%) and POTS (-23.3±12.0%) compared to controls (-4.4±7.1%,p<0.001). Orthostatic end-tidal CO₂ was reduced in HYCH (27.9±5.6 mmHg) and POTS (27.1±5.6 mmHg) compared to controls (35.3±4.8 mmHg, p<0.001). Orthostatic heart rate was higher in POTS (117±19.3 BPM) compared to HYCH (88.5±15.0 BPM, p<0.001). Mild autonomic failure was present in 91.7% of HYCH and 82.7% of POTS patients. Compared HYCH with POTS, there was no significant difference in the following QASAT scores: sympathetic sudomotor (1.7±1.6/1.3±1.8, HYCH/POTS), parasympathetic cardiovagal (0.4±0.7/0.3±0.6), sympathetic adrenergic (1.2±0.9/1.1±1.0), epidermal fiber density (EFD, 1.8±2.1/1.9/2.4) and sweat gland fiber density (SGF, 1.4±2.0/1.5±2.3). EFD/SGF was abnormal in 63.4%/41.5% of HYCH and 55.8%/43.1% of POTS. Autoimmune markers were positive in 75% of HYCH and 81.5% of POTS. There was no significant difference in supine and orthostatic norepinephrine in both conditions.

Conclusions:

POTS and HYCH have similar abnormalities on subjective and objective measures except for the presence of tachycardia in POTS. Considering that the POTS-grade orthostatic tachycardia (≥30 BPM) can be seen in healthy subjects, these results suggest that HYCH and POTS represent a spectrum of the same disorder.