Manual quantitative assessment of amplitude and sleep stage distribution of excessive fragmentary myoclonus.

Introduction: Excessive fragmentary myoclonus (EFM) consists of brief, asynchronous, twitch-like movements appearing asymmetrically in sleep. The new AASM Manual for the Scoring of Sleep and Associated Events identifies some EFM scoring criteria but does not provide amplitude criteria for scoring EFM. Older observational series have used 50 mu Vs. We report data from various amplitude criteria using blinded comparisons. Methods: EFMs were analyzed on the polysomnograms of 8 patients (7 men and 1 woman, mean age 57 years, range: 47-79) using a standardized protocol for sensitivity, tonus threshold, impedance, amplitude measurements, and sleep stage. The first 20 minutes each of wake, Stage 1-2, SWS, and REM were analyzed. EFMs >= 25, >= 40, and >= 50 microvolts (mu Vs) in negative deflection above the baseline were counted in tibialis anterior muscle electromyography (EMG) channels bilaterally. Results: The mean EFM Index per minute for wake, regardless of impedance, was: 7.19 +/- 5.90 for >= 25 mu V amplitude; 2.43 +/- 2.02 for >= 40 mu Vs; and 2.08 +/- 2.23 for >= 50 mu Vs. For sleep stages, the EFM index by stage and amplitude criteria used for measurements were: Stage 1-2: 7.38 +/- 5.79 for >= 25 mu Vs; 3.13 +/- 3.33 for >= 40 mu Vs; and 2.36 +/- 2.66 for >= 50 mu Vs; SWS: 10.05 +/- 8.04 for >= 25 mu Vs; 2.71 +/- 3.13 for >= 40 mu Vs; and 1.38 +/- 1.92 for >= 50 mu Vs; Total REM: 15.96 +/- 11.32 for >= 25 mu Vs; 6.32 +/- 4.25 for >= 40 mu Vs; and 3.94 +/- 3.73 for >= 50 mu Vs; Phasic REM: 19.69 +/- 15.45 for >= 25 mu Vs; 8.63 +/- 7.06 for >= 40 mu Vs; and 5.52 +/- 6.44 for >= 50 mu Vs; Non-phasic REM: 13.93 +/- 11.31 for >= 25 mu Vs; 5.16 +/- 3.57 for >= 40 mu Vs; and 3.20 +/- 2.92 for >= 50 mu Vs. Conclusion: EFM rates increase with SWS and total REM with the highest EFM rates occurring during phasic REM. EFM rates were increased across all sleep stages when impedance was > 30 K Omega.