Routine Neurophysiologic Tremor Analysis as a Diagnostic Tool for Essential Tremor: A Prospective Study

Abstract

The objective of the current study was to investigate the diagnostic potential of the routine tremor neurophysiologic analysis for the diagnosis of essential tremor (ET) in patients with postural tremor syndrome. Three hundred consecutive outpatients attending for postural tremor were included. Accelerometry and surface electromyography was performed between 1 and 4 weeks after the first clinical visit. A final clinical diagnosis (mean follow-up period, 53 months) of the postural tremor syndrome was made by two neurologists blind to the neurophysiologic results. Six neurophysiologic criteria for the diagnosis of ET were applied to define the neurophysiologic examination as compatible or not compatible with ET (all criteria must be present): (1) rhythmic burst of postural tremor on EMG; (2) tremor frequency greater than or equal to 4 Hz; (3) absence of rest tremor or, if present, frequency 1.5 Hz lower than the postural tremor; (4) absence of tremor latency from rest to postural position; (5) changes of the dominant frequency peak less or equal to 1 Hz after the weight load test; and (6) no changes in tremor amplitude after mental concentration. The neurophysiologic criteria for ET showed a sensitivity of 97.7%, a specificity of 82.3%, a positive predictive value of 95.1%, a negative predictive value of 91.1%, and positive probability ratio of 5.5. The odds ratio was 198.43 (95% CI, 66.03 to 596.35). For the diagnosis of ET in patients with postural tremor, routine neurophysiologic tests have high diagnostic and predictive value that justifies its practice in movement disorders clinics.