Documentation of tremor in patients with central nervous system lesions. A clinical report.

Tremor is described by Stein and Lee as an "involuntary movement characterized by a rhythmic oscillation about a fixed point or trajectory during activities controlled by the central nervous system." Among such oscillations are those demonstrated by healthy individuals and referred to as physiological tremors. These tremors are associated with posture or voluntary movement and are enhanced during tonic activation of the muscle, with fatigue and anxiety, and under conditions of increased metabolism. The frequency of physiological tremors (8-12 Hz) is greater than the frequencies of resting tremors (4-7 Hz) and of clonus (5-8 Hz), which are associated with abnormal neurologic states. Although the Cybex® II dynamometer* has been used to document conditions such as paresis, reciprocal delays, and spasticity, the therapists at this facility do not believe it has been used to document the presence of tremor in patients who have had central nervous system lesions. Because tremors are important in the "diagnosis and localization of disease of the nervous system," their documentation often is included in the physical therapy assessment of patients with central nervous system lesions. The purpose of this clinical report is to describe the tremors we have observed using the Cybex® II dynamometer during routine velocity spectrum testing of brain injured patients. Our dynamometer testing has revealed rhythmic oscillations in both the elbow flexion and knee extension torque curves of brain injured patients (eg, those with closed head injuries, cerebral palsy, or cerebrovascular accidents). The oscillations have been observed rarely in the range of motion (electrogoniometer) curves obtained during such testing. During testing, we have noted most measurable tremors on the 30 ft-lb† torque scale using the 25 mm/sec paper speed and the damping recommended by the manufacturer for the joint being tested. The more sensitive 30 ft-lb scale allows the oscillations to be detected and measured. The 25 mm/sec paper speed spreads out the oscillations so they are more apparent and so their frequency can be measured by counting the number of cycles a second (by millimeter of paper length). The relative insensitivity of the range of motion scale in comparison with the torque scale (3.0°/division vs 1.0 ft-lb/ Figure. Tremor of 10 Hz during knee extension at 30,60, and 120°/ sec. All recordings were made using the 30 ft-lb torque scale and the 25 mm/sec paper speed.