Correlation of proximal and distal muscle strength with upper limb functional ability in patients with essential tremor

Despite being considered as a benign, genetic and monosymptomatic disorder, ET is a poorly understood entity with etiological and pathological heterogeneity. The aim of the present study was to examine the relation between proximal and distal muscle strength and upper limb functionality and tremor severity in patients with essential tremor (ET). The study enrolled 25 tremor patients followed at the neurology clinic of a university hospital and 19 healthy controls. Demographic data, risk factors, disease duration and dominant hand of the participants were recorded. Back and leg strength was assessed using a back and leg dynamometer and hand dynamometer and pinchmeter were used to determine hand strength. Functional ability of the participants was evaluated using the Minnesota Manual Dexterity Test (MMDT), Perdue Pegboard (PPBT) and Nine Hole Peg Test (NHPT). Tremor severity was assessed using the Fahn-Tolosa-Marin Tremor Rating Scale (FTMTRS) and the Lower Extremity Clinical Tremor Assessment Scale (LECTAS). A significant difference was found in the average back and leg muscle strength between ET patients and healthy controls (p < 0.05). The mean values for right/left hand muscle strength were not significantly different between the two groups (p > 0.05). Among the upper limb functional ability tests, significant differences were found between the two groups in the mean time to complete NHPT, Minnesota placing subtest and PPBT test (p < 0.05). While gender and risk factors were not significantly different between the two groups (p > 0.05), there was a significant difference with respect to the educational level (p < 0.01). No significant difference was found between back and leg muscle strength and FTMTRS and LECTAS (p > 0.05). A negative correlation and a significant association were found between average strength measurements obtained with the left hand dynamometer and FTMTRS in the ET group (p = 0.030, r = − 0.434). A positive correlation and a significant association were found between left hand strength and mean turning time in the MMDT in the control group (p = 0.041, r = 0.473). ET patients experience loss of proximal muscle strength and functional disability. Further studies are planned to investigate the effects of physical therapy modalities targeting increased proximal muscle strength on tremor severity and functional ability in ET patients.