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Abstract Details

Microneurographic findings in patients with POTS

Background: Postural tachycardia syndrome (POTS) is a form of chronic orthostatic intolerance with established diagnostic criteria. Its hallmark is an abnormal increase in heart rate with assumption of upright posture in the absence of orthostatic hypotension. It is assumed that POTS can be the result of a series of pathophysiologies, including among them an autonomic neuropathy. Microneurography can detect C fibre abnormalities. Moreover, a recent method has been described to determine whether sympathetic axons are depolarised in disease states.
Methods: Eight patients with the diagnosis of POTS according to current diagnostic criteria were referred for microneurographic assessment to rule out small nerve fibre involvement. Single C nerve fibre recordings were obtained from the superficial peroneal nerve. All C fibres belonging to the C-nociceptor and the C-sympathetic efferent classes were analysed. Measures of activity-dependent slowing of conduction velocity, the presence of abnormal spontaneous ongoing activity in nociceptors and resting conduction velocity (CV) were analysed. Analysis of the recovery cycle (RC) of excitability in sympathetic axons was obtained in 4 of the patients and compared to recent published data on the effect of membrane depolarisation on sympathetic axons.
Results: Spontaneous activity in C-nociceptors was present in 5/8. All of these 5 patients had concomitant neuropathic pain. There were no statistically significant differences in resting CV, or slowing at low (0.25Hz) and high rates (2Hz) of stimulation between C-nociceptors and sympathetic axons when compared to historical data. The RC was abnormal in 3 of the 4 recorded patients, suggesting relative membrane depolarisation.
Discussion: Microneurography can detect small nerve fibre involvement in POTS. Spontaneous activity in C-nociceptors was only detected in patients with concomitant neuropathic pain.  A specific involvement of sympathetic efferent axons can be demonstrated studying the recovery cycle of excitability.

TitleForenamesSurnameInstitutionLead AuthorPresenter
DrJordiSerraDepartment of Clinical Neurophysiology, King’s College Hospital, London
 NicholasGallDepartment of Cardiology, King’s College Hospital, London
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