Three-dimensional measurement of essential tremor

A mechanical linkage device was used to measure the three-dimensional posit ion of the fingertip during a postural task. Thirty patients with essential tremor were tested simultaneously with the device, uniaxial accelerometry. and clinical tremor measures. Eighteen patients were tested again 16 +/- 4 days later. The device accurately recorded the three-dimensional behavior of essential tremor. Measures from the device included mean three-dimension al velocity, mean three-dimensional dispersion, and power of the three-dime nsional acceleration. The logarithms of these measures were strongly correl ated (r = .841-.984) with all clinical measures including self-reported tre mor disability. The device measures were reliable within and between testin g sessions (intraclass correlation coefficients = .971-.977). The performan ce of the device was superior to uniaxial accelerometry, most likely as a r esult of the three-dimensional nature of the measurements. We conclude that essential tremor can be validly and reliably quantified during a postural task providing the recording device records movement in three dimensions an d the measurements are logarithmically transformed.