[Clinical and physiological studies on senile tremor]

We examined 6 male and 10 female patients with senile tremor which started at 60 years of age or older. The patients' age on examination ranged from 66 to 82 years (mean: 73.4; SD: 5.4 years). The surface electromyogram (EMG) was recorded from the bilateral biceps brachii, triceps brachii, forearm flexor and forearm extensor muscles. The frequency of the tremor was counted and patterns of grouping discharges were analysed. The effect of mechanical perturbation to the affected muscle on tremor rhythm was also examined. The same investigations were performed in 15 male and 7 female patients with essential tremor with onset age before 60 years as control patients. The mean frequency was 6.2 Hz (SD: 1.3 Hz) in senile tremor and 7.3 Hz (SD: 1.5 Hz) in essential tremor. There was a significant difference between the two groups. The mean frequency in control patients whose age on examination was 60 years or over was, however, 6.0 Hz (SD: 0.8 Hz), and there was no difference from the mean frequency in senile tremor. The frequency in both groups was inversely correlated to the patient's age on examination. The antagonist muscles were reciprocally discharged in 15 patients in the senile tremor group and in 7 in the controls. Mechanical perturbation of the affected muscle re-set the tremor rhythm in all patients examined. Thus, senile tremor had characteristics resembling tremor in the control patients, suggesting that senile tremor may be a subtype of essential tremor.