Tremors in CIDP: A Wrist Perturbation Study

Abstract

Chronic inflammatory demyelinating polyneuropathy (CIDP) is characterized by sensory and motor deficits. Tremor is a frequent and severe symptom in patients suffering from CIDP. There is limited and contradictory data regarding the effect of tremor on treatment of the underlying polyneuropathy, and on treatment specifically aimed at neuropathic tremor. The pathophysiology of the CIDP tremor is unknown, but there are speculations about both a peripheral and central origin. From previous studies, it is seen that if a tremor’s frequency is substantially load-independent, entrained exclusively by comparable driving frequencies, and only minimally phase-reset by torque pulses, it is considered to be primarily of central origin. A wrist perturbation study using a wrist manipulator was conducted on CIDP patients, with tremors (n=8) and without tremors (control, n=8) to address these speculations, and to understand the characteristics of this neuropathic tremor. The perturbation study involved studying the effects of entrainment perturbations, spring loading via changing the virtual spring stiffness, ramp-and-hold stretches to evoke stretch reflexes, along with the estimation of admittance. The entrainment task showed subharmonic and superharmonic peaks of power spectral densities of EMG in
tremor subjects. Compared to controls, the tremor patients had significantly reduced stiffness, which could be attributed by the loss of muscle strength, and thus the tremor advertently affects muscle activation. No significant difference in M1, and M2 amplitude responses, and reflex latencies were found between the tremor and control group.