The Pathophysiology Of Neuropathic And Non-Neuropathic Postural Tachycardia Syndrome

[RichGotsPots]

http://www.neurology.org/cgi/content/meeting_abstract/78/1_MeetingAbstracts/P05.203

C1 Autonomic Disorders: Orthostatic and Autoimmune Disorders

The Pathophysiology of Neuropathic and Non-Neuropathic Postural Tachycardia Syndrome (P05.203)

Christopher Gibbons1, Istvan Bonyhay2, Adam Benson3 and Roy Freeman4

1 Beth Israel Deaconess Medical Center Boston MA

2 Neurology Beth Israel Deaconess Medical Center Boston MA

3 Neurology Beth Israel Deaconess Medical Center Boston MA

4 Neurology Beth Israel Deaconess Medical Center Boston MA

Objective: To define the clinical characteristics, fatigue severity, autonomic function and differentiating factors in individuals with neuropathic and non-neuropathic POTS.

Background Postural tachycardia syndrome (POTS) is an increased heart rate in the upright position with orthostatic intolerance. Some patients with POTS have an underlying small fiber neuropathy.

Design/Methods: Fourteen patients (10F) with POTS and 8 healthy control subjects (5F) underwent skin biopsy analysis of intra-epidermal nerve fiber density (IENFD), quantitative sensory testing (QST) and autonomic testing. Subjects completed quality of life, fatigue and disability questionnaires. Subjects were separated into neuropathic and non-neuropathic POTS, defined by abnormal IENFD and/or heat and heat-pain detection thresholds. Differences in autonomic function and symptom questionnaires were analyzed by t-test with corrections for multiple analyses. Significance set at P<0.05.

Results: Participants with POTS had lower IENFD at the distal leg and distal thigh than control subjects (P<0.05) but no differences in quantitative sensory testing. Participants with POTS had significantly greater fatigue, anxiety, physical impairment, orthostatic intolerance and perceived disability than controls (P<0.0001 all questionnaires). Seven patients had neuropathic and seven had non-neuropathic POTS. Neuropathic patients had higher supine blood pressures (P<0.05), with higher heart rates (P<0.05), lower 30:15 ratio's (P<0.05) and lower Valsalva ratios (P<0.05). There were no differences in any self-reported questionnaires between neuropathic and non-neuropathic POTS.

Conclusions: Patients with neuropathic and non-neuropathic POTS have a similar symptom profile, fatigue level and disability. POTS subtypes can only be distinguished by evaluation for small fiber neuropathy. There were differences in autonomic tests (higher blood pressure and heart rate, lower 30:15 and Valsalva ratio) consistent with underlying small fiber dysfunction. These findings suggest that neuropathic and non-neuropathic POTS have different pathophysiological mechanisms that underlie the postural tachycardia. These findings have implications for therapeutic interventions to treat this disorder.