Cardiovascular autonomic dysfunction in Morvan syndrome: A comparative study of heart rate variability and cardiovascular autonomic reflex tests.
BACKGROUND AND OBJECTIVE Morvan syndrome is a rare neurological disorder characterized by peripheral nerve hyperexcitability, autonomic instability, and encephalopathy. Autonomic dysfunction in these patients may have important cardiovascular implications. We characterized cardiovascular autonomic function in Morvan syndrome and compared it with that of healthy controls. METHODS In this comparative cross-sectional study, 19 patients with Morvan syndrome and 24 healthy controls broadly comparable in age at the group level were evaluated. Heart rate variability (HRV) was assessed using non-invasive electrocardiography, including time-domain and frequency-domain measures. Autonomic function was evaluated using Ewing's battery, including heart-rate response to deep breathing, Valsalva maneuver, orthostatic testing, and isometric handgrip. RESULTS Morvan syndrome patients showed significant autonomic impairment compared with healthy controls. HRV parameters, including standard deviation of NN intervals (SDNN), root mean square of successive differences (RMSSD), total power, low-frequency power, and high-frequency power, were significantly reduced in patients. Ewing's battery also demonstrated marked abnormalities, including reduced deep-breathing difference, lower Valsalva ratio, impaired orthostatic blood pressure response, and diminished isometric handgrip response. Effect sizes ranged from moderate to large (0.504-0.934), indicating substantial clinical relevance. Disease duration showed significant negative correlations with several HRV indices, including RMSSD (r=-0.68, P=0.001), suggesting progressive autonomic impairment. CONCLUSION Morvan syndrome patients demonstrated significant cardiovascular autonomic dysfunction compared with healthy controls, reflected by impaired HRV and abnormal autonomic reflex testing. These findings support the value of routine HRV and Ewing's battery assessment in Morvan syndrome for early detection of cardiovascular autonomic involvement and improved clinical monitoring.