Current Case: Winter 2019

Case Presentation

Contributed by Omar Danoun, MD and Lily Wong-Kisiel, MD, Mayo Clinic Rochester

A 53 year old woman presented for evaluation of chronic fatigue and cognitive difficulties over the last 5 years. An initial electroencephalogram (EEG) reportedly showed frequent subclinical seizures originating from the left and right parieto-occipital head regions. Brain MRI showed mild leukoaraiosis and FDG-PET scan showed mild bilateral temporal (mesial and neocortical) hypometabolism and sensorimotor cortex bilaterally but did not fit any neurocognitive pattern. Neuropsychological evaluation showed normal and nonspecific changes. She was started on a trial of levetiracetam 250 mg BID after her initial EEG that was thought to be frequent subclinical seizures.  Prolong video EEG recording showed frequent posteriorly dominant rhythmic delta activity lasting between 2-23 seconds (Figures 1-2) which had an abrupt onset and offset. During wakefulness, the patient remained alert and answered questions correctly during these EEG findings. These posteriorly dominant rhythmic delta activity also occurred during drowsiness and sleep (Figure 3).

Question 1: What does the EEG in Figures 1-3 show?

  1. Subclinical occipital seizure
  2. Benign variant
  3. Interictal occipitally predominant spike and slow wave discharges
  4. Occipital intermittent rhythmic delta activity (OIRDA)
Answer: (click here)

A1: Correct answer: B. Benign variant

Question 2: What is the overall risk of seizures in individual with the EEG findings shown in Figures 1-3?

  1. Same as in general population
  2. Slightly increased than general population
  3. Significantly increased than general population
Answer: (click here)

A2: Correct answer: A. Same as in general population

Discussion: (click here)

The EEG showed intermittent rhythmic discharges of delta range that look maximal posteriorly on the longitudinal bipolar and average referential montages. The patient remained asymptomatic during the rhythmic delta discharges, which were without evolution in topography, morphology and frequency. The EEG is therefore not an ictal pattern but consistent with benign variants, such as subclinical rhythmic electrographic discharges of adults (SREDA) or slow alpha variant (SAV), both with low risk for epilepsy.

SREDA was first described by Westmoreland and Klass in 1981(1). SREDA presents in patients over 50 years of age and is sharply contoured, mostly theta range discharges of 5-7 Hz, localizes to temporo-parietal regions and not followed by slowing after the discharges. SREDA is a distinctive rare normal variant of unclear clinical significance, with an estimated prevalence of 1/2500 EEG recordings (Westmoreland 1996). Due the infrequent occurrence and the resemblance to electrographic seizures, SREDA is often misinterpreted as an abnormal finding and sometimes as seizures. In contrast to electrographic seizures, SREDA does not evolve in frequency, morphology or distribution (figure 4). Atypical presentations of SREDA include predominant delta frequency, frontal or focal distribution, prolonged duration, notched waveforms or occurrence during sleep (2).  SAV is a sub-harmonic of normal alpha rhythm usually at the ratio of two to one to the native background frequency. SAV is symmetric and synchronous, alternates with the normal alpha rhythm, restricted to the occipital area, and often with a notched appearance (figure 5). SAV attenuates with eye opening and is often enhanced by hyperventilation (3).  In the case presented above, the notched appearance in the occipital area could be due to the presence of overriding occipital alpha rhythm.

The EEG from the case presentation showed notched appearance but did not have after-slowing nor disturbance the background, and therefore not consistent with occipital spike and wave discharges.  Occipital intermittent rhythmic delta activity (OIRDA) is rhythmic delta waves that are confined to the occipital region, either symmetrically or asymmetrically, present during relaxed wakefulness with eye closure and attenuates with eye opening, and augmented by hyperventilation (figure 6). OIRDA is associated with generalized epilepsy syndromes, and seen in 11% and 60% of patients with childhood absence epilepsy (4).  

References

  1. Westmoreland BF, Klass DW. A distinctive rhythmic EEG discharge of adults. Electroencephalogr Clin Neurophysiol 1981;51(2):186–191.
  2. Westmoreland BF, Klass DW. Unusual variants of subclinical rhythmic electrographic discharges of adults (SREDA). Electroencephalogr Clin Neurophysiol. 1997 Jan;102(1):1-4.
  3. Schmitt SE. Generalized and lateralized rhythmic patterns. J Clin Neurophysiol. 2018 March; 35: 218–228.
  4. Gullapalli D, Fountain NB. Clinical correlation of occipital intermittent rhythmic delta activity. J Clin Neurophysiol. 2003 Feb;20(1):35-41.

Current Case: Winter 2019

Case Presentation

A 53 year old woman presented for evaluation of chronic fatigue and cognitive difficulties over the last 5 years. An initial electroencephalogram (EEG) reportedly showed frequent subclinical seizures originating from the left and right parieto-occipital head regions. Brain MRI showed mild leukoaraiosis and FDG-PET scan showed mild bilateral temporal (mesial and neocortical) hypometabolism and sensorimotor cortex bilaterally but did not fit any neurocognitive pattern. Neuropsychological evaluation showed normal and nonspecific changes. She was started on a trial of levetiracetam 250 mg BID after her initial EEG that was thought to be frequent subclinical seizures.  Prolong video EEG recording showed frequent posteriorly dominant rhythmic delta activity lasting between 2-23 seconds (Figures 1-2) which had an abrupt onset and offset. During wakefulness, the patient remained alert and answered questions correctly during these EEG findings. These posteriorly dominant rhythmic delta activity also occurred during drowsiness and sleep (Figure 3).

Question 1: What does the EEG in Figures 1-3 show?

  1. Subclinical occipital seizure
  2. Benign variant
  3. Interictal occipitally predominant spike and slow wave discharges
  4. Occipital intermittent rhythmic delta activity (OIRDA)
Answer: (click here)

A1: Correct answer: B. Benign variant

Question 2: What is the overall risk of seizures in individual with the EEG findings shown in Figures 1-3?

  1. Same as in general population
  2. Slightly increased than general population
  3. Significantly increased than general population
Answer: (click here)

A2: Correct answer: A. Same as in general population

Discussion: (click here)

The EEG showed intermittent rhythmic discharges of delta range that look maximal posteriorly on the longitudinal bipolar and average referential montages. The patient remained asymptomatic during the rhythmic delta discharges, which were without evolution in topography, morphology and frequency. The EEG is therefore not an ictal pattern but consistent with benign variants, such as subclinical rhythmic electrographic discharges of adults (SREDA) or slow alpha variant (SAV), both with low risk for epilepsy.

SREDA was first described by Westmoreland and Klass in 1981(1). SREDA presents in patients over 50 years of age and is sharply contoured, mostly theta range discharges of 5-7 Hz, localizes to temporo-parietal regions and not followed by slowing after the discharges. SREDA is a distinctive rare normal variant of unclear clinical significance, with an estimated prevalence of 1/2500 EEG recordings (Westmoreland 1996). Due the infrequent occurrence and the resemblance to electrographic seizures, SREDA is often misinterpreted as an abnormal finding and sometimes as seizures. In contrast to electrographic seizures, SREDA does not evolve in frequency, morphology or distribution (figure 4). Atypical presentations of SREDA include predominant delta frequency, frontal or focal distribution, prolonged duration, notched waveforms or occurrence during sleep (2).  SAV is a sub-harmonic of normal alpha rhythm usually at the ratio of two to one to the native background frequency. SAV is symmetric and synchronous, alternates with the normal alpha rhythm, restricted to the occipital area, and often with a notched appearance (figure 5). SAV attenuates with eye opening and is often enhanced by hyperventilation (3).  In the case presented above, the notched appearance in the occipital area could be due to the presence of overriding occipital alpha rhythm.

The EEG from the case presentation showed notched appearance but did not have after-slowing nor disturbance the background, and therefore not consistent with occipital spike and wave discharges.  Occipital intermittent rhythmic delta activity (OIRDA) is rhythmic delta waves that are confined to the occipital region, either symmetrically or asymmetrically, present during relaxed wakefulness with eye closure and attenuates with eye opening, and augmented by hyperventilation (figure 6). OIRDA is associated with generalized epilepsy syndromes, and seen in 11% and 60% of patients with childhood absence epilepsy (4).  

References

  1. Westmoreland BF, Klass DW. A distinctive rhythmic EEG discharge of adults. Electroencephalogr Clin Neurophysiol 1981;51(2):186–191.
  2. Westmoreland BF, Klass DW. Unusual variants of subclinical rhythmic electrographic discharges of adults (SREDA). Electroencephalogr Clin Neurophysiol. 1997 Jan;102(1):1-4.
  3. Schmitt SE. Generalized and lateralized rhythmic patterns. J Clin Neurophysiol. 2018 March; 35: 218–228.
  4. Gullapalli D, Fountain NB. Clinical correlation of occipital intermittent rhythmic delta activity. J Clin Neurophysiol. 2003 Feb;20(1):35-41.