Benign Epileptiform Transients of Sleep (BETS), also referred to as Small Sharp Spikes (SSS), are a common and benign finding observed during the drowsy and sleep stages in an EEG. These transients can appear similar to epileptiform spikes, which are typically associated with seizure activity. However, BETS are not pathological and are considered a normal occurrence, especially in healthy individuals. They are brief, low-amplitude, and typically appear in specific areas of the brain, making them easily distinguishable from seizures.

Key Features of BETS

  • Low Amplitude: BETS have a very low amplitude, typically under 50µV. This differentiates them from epileptiform spikes, which generally have a higher amplitude.
  • Short Duration: These transients are brief, usually lasting less than 100 milliseconds. This short duration helps distinguish them from epileptiform discharges, which can last longer.
  • Location: BETS are most commonly observed in the temporal regions of the brain, though they can also be found in other areas. The temporal chains (the series of electrodes placed along the temporal region) are the most typical locations for these findings.
  • Sleep Context: BETS are exclusively seen during sleep or drowsiness, and not during periods of wakefulness. Their presence outside of sleep would be more concerning.
  • Sharp Wave Appearance: The morphology of BETS consists of sharp waves or spikes that resemble those of epileptiform discharges, but they do not evolve into more complex or pathological patterns.

When and Where BETS Appear

BETS are commonly seen during the transition between wakefulness and sleep, especially as an individual enters drowsiness or the light sleep stages (Stage 1 and Stage 2 of non-REM sleep). They are frequently observed in the temporal lobes and may occur unilaterally (on one side of the brain) or bilaterally. The presence of BETS in these areas is typical, but they can also be seen in other regions of the brain.

Differentiating BETS from Epileptiform Discharges

Distinguishing BETS from actual epileptiform discharges is crucial, as epileptiform discharges are associated with conditions like epilepsy. Here are the key differentiating factors:

  • Low Amplitude: The low amplitude of BETS (typically under 50µV) is a key characteristic. Epileptiform spikes are usually higher in amplitude and may appear more prominent on the EEG.
  • Duration: BETS are brief, lasting less than 100 milliseconds, and do not evolve into a longer event, while epileptiform spikes tend to be longer and more complex, potentially lasting several seconds.
  • Evolution: Unlike epileptiform discharges, which can evolve into a slow wave or spread to other brain areas (especially in seizures), BETS do not change in form or spread to different areas. They remain isolated, short, and low amplitude.
  • Sleep Context: BETS are primarily seen during sleep and drowsiness. If epileptiform discharges appear during wakefulness, they are more likely to be pathological and need to be evaluated for seizures or other conditions.
  • Recurrent Occurrence: If BETS are isolated and occur rarely, they are likely benign. However, if they appear frequently or in combination with other abnormal EEG findings, this may warrant further investigation.

Clinical Significance of BETS

BETS are considered a normal variant and do not indicate any underlying neurological disorder. They are often seen in both healthy individuals and those with certain neurological conditions, especially during sleep. Their presence should not cause alarm unless they begin to appear frequently, evolve into more complex patterns, or are associated with other abnormal findings on the EEG. They are typically not associated with seizures or epilepsy but should be monitored for changes over time.

Possible Concerns

While BETS are benign, there are a few scenarios where further investigation may be warranted:

  • Increased Frequency: If BETS begin to occur more frequently or become more prominent, it may be useful to perform further analysis, as an increased frequency could indicate an underlying issue or could be a precursor to other EEG abnormalities.
  • Presence During Wakefulness: If BETS are detected outside of sleep or drowsiness, particularly during wakefulness, this may be indicative of a seizure or another pathological condition, and it requires immediate clinical attention.
  • Combination with Other Abnormalities: If BETS are seen alongside other more concerning EEG findings, such as generalized spikes, slowing, or epileptiform discharges, this may suggest an underlying neurological condition that requires further evaluation.

When to Seek Medical Advice

If BETS are identified on an EEG and the patient has no history of seizures or neurological disorders, there is usually no cause for concern. However, if there is any doubt, or if the pattern begins to change over time, it is important to consult a neurologist or EEG specialist for further evaluation. If the patient has a history of seizures or other neurological issues, a follow-up EEG may be warranted to ensure the patterns do not evolve into more serious conditions.

Conclusion

Benign Epileptiform Transients of Sleep (BETS) are a normal EEG finding that typically appears in the temporal regions during drowsiness and sleep. They are characterized by low amplitude, short duration, and a sharp-wave morphology. While they may resemble epileptiform discharges, they are benign and usually do not require intervention. Recognizing and distinguishing BETS from pathological epileptiform discharges is an essential skill in EEG interpretation. If the pattern remains stable, there is no need for concern; however, if it changes or increases in frequency, further investigation may be needed.