The value of heart rate variability in autonomic nervous function evaluation and diagnosis of fatal familial insomnia

Background Fatal familial insomnia (FFI) is a rare autosomal dominant inherited prion disease characterized by prominent organic sleep‐related impairment accompanied by a series of symptoms with strong clinical heterogeneity in a rapid progression. As the most significant clinical feature and the potential diagnostic marker of FFI, progressive sympathetic symptoms were lack of a objective noninvasive quantitative method to detect. Method From May 2013 to August 2020, nine patients with FFI, eight patients with Creutzfeldt‐jakob disease (CJD) and nine normal control (NC) with matched sex and age were recruited in this study. All the participants underwent a nocturnal video‐polysomnography included a lead II electrocardiography (ECG). Heart rate variability analysis with successive 5 min (in time domain methods, frequency domain methods and non‐linear measurement) was performed during quiet wake before sleep and in the following N2, N3 and REM of the first sleep cycle. Result In FFI group, the continuous increased heart rate with the relatively decreased amplitude of the oscillations compared with NC and CJD group, revealed the axis of equilibrium shifts towards sympathetic activation. Furthermore, the RMSSD and HF during sleep stage in FFI were significantly lower than in NC group, which reflected the decreased activation of parasympathetic nervous system. The significant abnormal LF/HF ratio and SD1/SD2 ratio in combination with the lower values of correlation dimension D2 in FFI group supported its unbalanced autonomic nervous function. Conclusion Dysfunctions of autonomic nerve system in patients with FFI may be affected by parasympathetic hypofunction partly except sympathetic activation, and HRV is expected to become a method in diagnosis for FFI.