28 September 2026
: Case report 
Coexisting Postural Orthostatic Tachycardia Syndrome on Autonomic Reflex Testing in Functional Neurologic Disorder
Unusual clinical course, Challenging differential diagnosis
Sushmita Das
AEF 1, Sri Rama Narayana Yerraballa AEF 1, Priyanka Shekhawat AEF 1*
DOI: 10.12659/AJCR.953323
Am J Case Rep 2026; 27:e953323
Table 3 Stepwise approach to orthostatic symptoms in patients with established functional neurological disorder (FND).
| Step | Action | Details |
|---|---|---|
| Initial clinical assessment | Elicit a focused orthostatic history (lightheadedness, presyncope, fatigue, cognitive symptoms), including triggers (prolonged standing, heat) and relieving factorsDocument symptom chronicity, functional impact, and presence of other paroxysmal events | |
| Bedside orthostatic vitals | Perform standardized supine-to-standing measurements with serial heart rate and blood pressure recordings over an adequate duration (eg, up to 10 minutes of upright posture, as tolerated) | |
| Interpretation of bedside testing | If diagnostic criteria for orthostatic hypotension or POTS are met → proceed with appropriate management | |
| Formal autonomic reflex testing | If repeat bedside testing remains non diagnostic or is not feasible, refer for comprehensive autonomic evaluation, including head-up tilt table testing with continuous hemodynamic monitoringIncorporate cardiovagal and adrenergic testing (eg, heart rate variability with deep breathing and the Valsalva maneuver) to assess parasympathetic function and sympathetic responses | |
| Risk modifiers | Lower threshold for escalation in the presence of features increasing pre-test probability, such as generalized joint hypermobility, multi-system autonomic symptoms, or high autonomic symptom burden (eg, elevated COMPASS-31 scores) | |
| Diagnostic integration | Interpret autonomic findings alongside positive clinical signs of FNDRecognize that functional and autonomic disorders may coexist and avoid attributing all symptoms to a single mechanismUse objective autonomic data to guide targeted management while continuing appropriate FND-directed therapy | |
| Abbreviations: COMPASS-31, Composite Autonomic Symptom Score-31; POTS, postural orthostatic tachycardia syndrome. | ||