Exploration of cardiac sympathetic adrenergic nerve activity in narcolepsy

To compare cardiac sympathetic adrenergic nerve activity in patients with narcolepsy type 1 (NT1) and controls using ¹²³I-MIBG myocardial scintigraphy, and to determine the clinical and neurophysiological variables associated with ¹²³I-MIBG scintigraphy results in NT1.

Fifty-six NT1 patients and 91 controls without neurological diseases underwent a cardiac scintigraphy. MIBG uptake was quantified by delayed heart/mediastinum (H/M) ratio. Clinical, neurophysiological and biological determinants of a low H/M were assessed in NT1.

MIBG uptake did not differ between NT1 and controls in crude and adjusted associations. Five patients had low MIBG uptake (<1.42, first decile of controls), often with advanced age, cardiovascular (CV) diseases, stimulants intake, and REM sleep behavior disorder. Patients with H/M <1.62 (lowest tertile) were older, with higher BMI, microarousal index and CV comorbidities. A three-fold increase of phasic/tonic REM sleep motor activities was found in those patients, confirmed in a subanalysis of 40 drug-free patients. No association was found with CSF hypocretin levels.

A direct measure of the heart adrenergic nerve activity revealed no sympathetic denervation in NT1.

Our results indicate normal cardiac sympathetic innervation in NT1. However, few patients with low MIBG uptake also presented CV comorbidities and REM sleep motor deregulation, potentially at high CV risk, requiring a careful follow-up.