Irregularity distinguishes limb tremor in cervical dystonia from essential tremor.

INTRODUCTION: Patients with cervical dystonia (CD) often have limb tremor that is clinically indistinguishable from essential tremor (ET). Whether a common central mechanism underlies the tremor in these conditions is unknown. We addressed this issue by quantifying limb tremor in 19 patients with CD and 35 patients with ET. METHOD: Postural, resting and kinetic tremors were quantified (amplitude, mean frequency and regularity) using a three-axis accelerometer. RESULTS: The amplitude of limb tremor in ET was significantly higher than in CD, but the mean frequency was not significantly different between the groups. The cycle-to-cycle variability of the frequency (ie the tremor irregularity), however, was significantly greater (approximately 50%) in CD. Analysis of covariance excluded the possibility that the increased irregularity was related to the smaller amplitude of tremor in CD (ANCOVA: p = 0.007, F = 5.31). DISCUSSION: We propose that tremor in CD arises from oscillators with different dynamic characteristics, producing a more irregular output, whereas the tremor in ET arises from oscillators with similar dynamic characteristics, producing a more regular output. We suggest that variability of tremor is an important parameter for distinguishing tremor mechanisms. It is possible that changes in membrane kinetics based on the pattern of ion channel expression underlie the differences in tremor in some diseases.

A portable hand-held device for quantifying and standardizing tremor assessment.

We describe the results of a hand-held device for quantifying tremor in the upper extremity. The specific aims of the study were to evaluate: (1) the reliability of the device to record tremor frequency and amplitude; (2) the relationship between observer ratings of tremor severity and spectral power derived from the instrument; (3) the effects of limb posture on tremor properties recorded by the instrument; and (4) whether scores from the instrument can discriminate types of tremor with sufficient accuracy to be of diagnostic value. Results from 242 subjects with tremor showed significant effects of limb posture on tremor frequency detected by the device which could not be revealed using traditional observer severity ratings. Subjects with tremor associated with idiopathic Parkinson's disease were distinguished from patients with drug-induced parkinsonian tremor with 83% accuracy. These and other findings on instrument validity demonstrate that tremor assessment can be performed using standard quantitative procedures which overcome many of the limitations inherent in subjective observer ratings. The portability of this instrument, referred to as the Tremorometer, makes it a useful tool for multi-site collaborative studies in community settings.

Plugs and stiletto: entry incisions for a 20-gauge instrument system.

A specialized stiletto shaped knife (Stiletto) and self-retaining incision plugs (Sclera Plugs) have been made. They are very useful for creating and temporarily occluding entry incisions for 20-gauge instruments suitable for closed eye intraocular surgery such as vitrectomy, lensectomy, removal of retina and vitreous membranes. The choice of material, configuration and dimensions of these new devices enable one to create incisions in the pars plana which do not leak liquid, gas, or tissue at IOP up to 80 mm Hg, when occupied by 20-gauge cylindrical instruments or Sclera Plugs. The plugs free one or both of the surgeon's hands for use outside the eye for indirect ophthalmoscopy, external surgery, and reduce considerably the time and skill formerly required for proper incision management.