Table 3.

Clinical characteristics which can predict the risk of ET patients developing into PD.

Clinical characteristics	Prodromal markers	References
Tremor	Circumscribed resting tremor	(44)
	Late onset asymmetrical postural tremor	(45)
	Jaw tremor in ET	(46, 47)
	A kinematic data: TSI	(48)
Non-motor symptoms	Olfactory decline (hyposmia/anosmia)	(49–51)
	Cognitive decline	(52–54)
	Sleep disorder, especially RBD	(55–59)
	RBD & autonomic symptoms	(60)

ET, essential tremor; PD, Parkinson's diseases; TSI, the tremor stability index; RBD, REM sleep behavior disorder.