Excessive Fragmentary Myoclonus
Authors: Stephen W. Cohen, MD (1) and Arthur S. Walters, MD (1)
Sleep Division, Dept of Neurology, Vanderbilt University Medical Center , Nashville, TN, USA.
Case
This is a 73 year old male who was sent by his primary care physician for an evaluation of excessive daytime somnolence and snoring. In addition, he has leg cramps, nocturia, and a remote history of acting out a dream. Medical history is significant for hypertension, depression, and recent stroke. Medications include aspirin, atorvastatin, fluoxetine, hydrochlorothiazide, lisinopril, and omeprazole.
His baseline polysomnogram is shown below in a 2 minute window
Question
What is the diagnosis?
- Periodic Limb Movements of Sleep (PLMS)
- REM Sleep Behavior Disorder (RBD)
- Excessive Fragmentary Myoclonus (EFM)
- Restless Legs Syndrome (RLS)
Answer: C. Excessive Fragmentary Myoclonus (EFM)
Discussion
Excessive Fragmentary Myoclonus (EFM) is characterized by EMG bursts with a typical maximum duration of 150 milliseconds, with a variable amplitude between 50 to several hundred microvolts lasting for at least 20 minutes of NREM sleep with at least 5 EMG bursts per minute. EFM is considered an incidental polysomnographic finding and does not require any specific treatment. It is more common in men and has been shown to occur in about 9% of the general population (Frauscher et al 2014). Usually any associated movements, if present, are too small to be seen on video.
Periodic Limb Movements of Sleep (PLMS) can be differentiated from EFM by longer movements (which last 0.5 to 10 seconds), which span a longer period between movements (5 to 90 seconds). REM Sleep Behavior Disorder (RBD) is characterized by excessive phasic leg EMG bursts similar to EFM, but these occur in REM sleep as opposed to NREM sleep, and commonly has sustained or phasic elevation in the chin EMG. In addition, the bursts of RBD tend to occur in clusters as opposed to the more isolated and more generally distributed bursts of EFM. The phasic bursts of RBD occur at rest and not during the more violent episodes of dream-enacting behavior. Restless Legs Syndrome (RLS) is a clinical diagnosis characterized by an urge to move the legs in wakefulness, worsening of the symptoms at rest and at night, with at least partial relief by activity. Although PLMS are common in RLS they are not required for the diagnosis.
References:
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American Academy of Sleep Medicine. International Classification of Sleep Disorders. 3rd ed (2014). Darien, IL American Academy of Sleep Medicine.
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Berry RB, Brooks R, Gamaldo CE, et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Darien, IL: American Academy of Sleep Medicine; 2017. Version 2.4.
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Frauscher, B., Gabelia, D., Mitterling, T., Biermayr, M., Bregler, D., Ehrmann, L., Hogl, B. (2014) Motor events during healthy sleep: A quantitative polysomnographic study. Sleep 37(4).
