Non-motor features of essential tremor with midline distribution

Midline essential tremor (Mid-ET) is a distinctive group of essential tremor (ET) in which tremor affects the neck, jaw, tongue, and/or voice. For long, it has been considered as an ultimate stage of the disease and a marker of its severity. However, recent studies pointed its complexity in terms of non-motor presentation. Thus, we aimed to investigate the non-motor signs (NMS) in Mid-ET.

We conducted a cross-sectional study in a tertiary neurology referral center including ET patients classified into two groups based on the presence or not of midline tremor (Mid-ET vs. No-Mid-ET). We assessed NMS using the non-motor severity scale (NMSS), a large battery of cognitive tests, clinical and electrophysiological study of the autonomic nervous system along with the evaluation of sleep disturbances.

A total of 163 patients were included: Mid-ET (n = 79) and No-Mid-ET (n = 84) matched in gender and age of onset. Mid-ET patients had higher proportion of late-onset ET (> 60 years old, p = 0.002) and more extrapyramidal signs (p = 0.005). For NMS, Mid-ET was marked with cognitive dysfunction (p = 0.008). The hallmarks of the neuropsychiatric profile of Mid-ET were executive dysfunction (p = 0.004), attention problems (p < 0.000), episodic memory impairment (p = 0.003), and greater depression (p = 0.010). The presence of RBD was a trait of Mid-ET (p = 0.039). In both Mid-ET and No-Mid-ET phenotypes, clinical and neurophysiological dysautonomia correlated with cognitive dysfunction.

Mid-ET patients had greater cognitive dysfunction, depression, RBD, higher proportion of late-onset ET, and more extrapyramidal signs. Taken all together, these findings could provide a redesigned insight into the underlying physiopathology of Mid-ET indicative of a greater cerebellar dysfunction.