Background Postural orthostatic tachycardia syndrome (POTS) is a disorder of orthostatic intolerance characterised by excessive tachycardia of unknown aetiology. Whether this condition involves abnormal cardiac sympathetic innervation or function remains elusive. Meta-iodobenzylguanidine (MIBG) resembles guanethidine and is a pharmacologically inactive analogue of norepinephrine, which is similarly metabolised in noradrenergic neurons. MIBG myocardial scintigraphy is used clinically to estimate local myocardial sympathetic nerve damage in some forms of heart disease and autonomic neuropathy. The objective of this study was to evaluate cardiac sympathetic innervation in patients with POTS.
Methods 20 patients with POTS were studied using 123I-MIBG-single photon emission computed tomography, standardised autonomic testing, assessment of catecholamine plasma levels and sympathetic skin response.
Results In four POTS patients (20.0%), myocardial MIBG uptake was markedly decreased. The mean heart to mediastinum ratio was reduced to 1.22±0.08 compared with the normal range of >1.7. No correlation was found between myocardial MIBG uptake and degree of postural tachycardia, baroreflex sensitivity, catecholamine plasma levels or other autonomic parameters. Sympathetic skin responses were normal in all patients.
Conclusions These findings suggest that POTS may be, in part, a manifestation of autonomic cardiac neuropathy. MIBG myocardial scintigraphy may be helpful to distinguish patients with neuropathic POTS from patients with orthostatic intolerance of other origin.
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This work was presented in part at the 60th Annual Meeting of the American Academy of Neurology, 15 April 2008, Chicago, USA.
Competing interests None.
Ethics approval The study was approved by the ethics committee of the University of Witten/Herdecke according to the revised Declaration of Helsinki.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.