A 36-year-old man with no significant past medical history presented to the sleep medicine clinic with a history of loud snoring, frequent awakenings, restless sleep, and excessive daytime sleepiness with Epworth Sleepiness Scale score of 9. Overnight split-night polysomnography (PSG) was performed due to high clinical suspicion for OSA. PSG demonstrated an apneahypopnea index (AHI) of 7.0 events/hour. Incidentally, rhythmic electroencephalogram (EEG) activity was noted by the sleep technician that was concerning for possible “seizure activity.”
QUESTION: What EEG abnormality is the seen as depicted by the red arrows in Figure 1 and Figure 2?
ANSWER: Rhythmic mid-temporal discharges (RMTD), a benign variant.
DISCUSSION
Figure 1 (red arrow) shows bursts of theta activity seen in the frontal, occipital, and central leads. Figure 2 (red arrow) shows sharply contoured rhythmic theta activity localized to the right and left temporal region.
Figure 1. Representative recording of a 30-second epoch during N1 sleep.
Figure 2. Representative recording of 10-second multi-channel sleep-deprived EEG.
RMTD, also known as rhythmic temporal theta bursts of drowsiness is a benign variant with an incidence of 0.5 to 2%.1 It is commonly seen in adolescents and young adults.2 RMTD is characterized by rhythmic theta waves ranging in frequency from 5 to 7 Hz, occurring most prominently over the mid temporal region, lasting from several seconds to up to a minute. Morphologically, they are sharply contoured with a notched or flat topped waves.3 RMTD centers reside within cortical tissues of inferior temporal lobes3 and may generate paroxysms which may be bilateral or unilateral. Bilateral paroxysms may appear independently or simultaneously with variable asymmetry and without evolution.4 In our patient, these discharges were seen only during wakefulness and stage 1 NREM sleep. The video PSG did not corroborate any movements suggestive of seizure. A sleep deprived multi-channel EEG with use of additional T1 and T2 electrodes was obtained to better delineate the underlying EEG rhythm.
Due to the rhythmic nature of RMTD, they tend to closely resemble ictal epileptiform or inter-ictal epileptiform discharges (IED). IEDs are characterized by spike or sharp waves, spike and slow wave complexes or polyspike and slow wave complexes in the absence of clinical seizures. Unlike RMTD, generalized epilepsy generates discharges with sudden onset and termination, which are bilaterally symmetrical and synchronous, with a characteristic pattern of evolution. These discharges are clearly distinguishable from the background activity, due to their morphology and higher amplitude. Focal epilepsy has discharges that are lateralized in origin.4
CONCLUSIONS
Sleep medicine physicians need to be cognizant of these uncommon rhythmic discharges and be able to differentiate these from rhythmic EEG discharges due to seizures.
DISCLOSURE STATEMENT
This was not an industry supported study. This work was supported by the National Institutes of Health Grants (HL095748 and HL095799 to S.P.); Patient-Centered Outcomes Research Institute (PCORI) contract (IHS-1306-2505 and 3394-UOA to S.P). The statements in this manuscript are solely the responsibility of the author and do not necessarily represent the views of the PCORI, its Board of Governors or Methodology Committee. The funding institutions did not have any role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. Dr. Parthasarathy reports grants from NIH/ NHLBI, grants from Patient Centered Outcomes Research Institute, grants from US Department of Defense, grants from NIH (National Cancer Institute) NCI, grants from US Department of Army, grants from Johrei Institute, personal fees from American Academy of Sleep Medicine, personal fees from American College of Chest Physicians, non-financial support from National Center for Sleep Disorders Research of the NIH (NHLBI), personal fees from UpToDate Inc., personal fees from Philips-Respironics, Inc., grants from Younes Sleep Technologies, Ltd., grants from Niveus Medical Inc., grants from Philips-Respironics, Inc., outside the submitted work; In addition, Dr. Parthasarathy has a patent UA 14-018 U.S.S.N. 61/884,654; PTAS 502570970 (Home breathing device). The above-mentioned conflicts including the patent are unrelated to the topic of this paper. The other authors have indicated no financial conflicts of interest. The work was conducted at University of Arizona, Tucson, AZ.
ABBREVIATIONS
- AHI
apnea-hypopnea index
- EEG
electroencephalogram
- IED
inter-ictal epileptiform discharge
- OSA
obstructive sleep apnea
- PSG
polysomnogram
- RMTD
rhythmic mid-temporal discharge
CITATION
Shetty S, Jaffer F, Parthasarathy S. Rhythmic electroencephalogram activity during polysomnography. J Clin Sleep Med 2016;12(10):1426–1428.
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