Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Hye Lim Lee, Ji-sun Kim, Hanjun Kim, Il soo Kim, Jae-whan Kim, Ye-eun Kim, Seong-beom Koh, Rayaz A. Malik.
Essential tremor (ET) is a common movement disorder characterized by postural or kinetic tremor. We aimed to evaluate median nerve enlargement in patients with ET using ultrasonography (USG). Thirty-eight hands from 19 patients with ET and 24 hands from 13 controls underwent nerve conduction studies (NCS) and USG at the wrist. Tremor severity was measured using the Fahn–Tolosa–Marin Tremor Rating Scale (FTM-TRS). The median nerve cross sectional area (mCSA) in USG and NCS parameters were compared using ANCOVA. We evaluated the correlation between mCSA and NCS parameters or FTM-TRS scores using linear regression analysis. mCSA was significantly larger (p<0.001) and NCS parameters were different in two groups. Also, mCSA was negatively correlated with part B and C scores of FTM-TRS (p<0.001 and p = 0.039, respectively). In conclusion, median nerve enlargement with the changes of NCS parameters was observed and correlated with the severity of tremor in patients with ET.
Essential tremor (ET) is a common movement disorder characterized by postural or kinetic tremor, and 85–95% of patients with ET exhibit involvement of the distal part of the upper extremities [1,2]. It usually presents as a bilateral postural 8–12 Hz tremor of the hands [3,4]. Overextended repetitive movement of the distal upper extremity could result in enlargement of the median nerve at the wrist because of cumulative trauma-related injury and these injuries may also lead to median neuropathy, including carpal tunnel syndrome (CTS) [5–7]. Thus, repetitive hand movement in ET could damage and lead to enlargement of the median nerve at the wrist.
We suggest that abnormal repetitive movement of the hands may result in nerve injury and subsequent CSA increase in patient with ET. We performed a study comparing the mCSA at the wrist between patients with ET and healthy controls. The mCSA in patients with ET was larger than that in healthy controls based on static and NCS parameters; motor terminal latency, CMAP amplitude, sensory SNAP amptlidue, and sensory velocity in the median nerve were significantly different between the patients with ET and healthy controls. We also evaluated the association between mCSA and tremor severity with FTM-TRS. The mCSA at the carpal inlet level was negatively correlated with part B and part C FTM-TRS scores in patients with ET.