Abstracts

Rationale: Subclinical rhythmic electrographic discharges in adults (SREDA) are considered benign EEG patterns. It is the rarest of the normal EEG variants. These patterns, however, are often mistaken for electrographic seizures (SZs) even by epileptologists at level IV epilepsy centers. Patients with SREDA EEGs may be treated with multiple antiseizure medications (ASMs). In the extreme, these patients are diagnosed with intractable epilepsy and providers request presurgical evaluation. Here we report five such patients referred to our center for epilepsy surgery, and our evaluation demonstrated that these patients did not have seizures, but purely frequent SREDA patterns.


Methods: From 2013 to 2021, we identified 5 patients (Pts) who were referred from outside hospital (OSH) to us for epilepsy surgery evaluation because they had failed multiple (4-8) ASMs. One pt also had a Vagus Nerve Stimulation device. Their OSH EEGs reported 12-17 seizures (SZs) per day. However, our prolonged (5 to 8 days) video-EEG recorded frequent SREDA without epileptic seizures. All patients had a normal MRI. Other studies as part of presurgical evaluation such as PET, MEG or SPECT were performed.


Results: Pt#1 had non-episodic memory and spelling difficulties. OSH EEG reported 17 left temporal SZs/day. Our EEG showed frequent SREDA from left more than right temporal regions. Pt#2 had episodic symptoms of dizziness, hearing noises and staring off. OSH EEG reported 14 right temporal SZs/day. Our EEG showed frequent SREDA in the right temporal region. Pt#3 had non-episodic symptoms of waves of exhaustion and memory difficulties. OSH EEG reported frequent subclinical left temporal SZs. Our EEG showed frequent SREDA from left more than right temporal regions. PT#4 had episodic symptoms of hearing “wind in the head” and impaired speech. OSH EEG reported more than 12 SZs/day. Our EEG showed frequent SREDA from right more than left temporo-parietal regions. Pt#5 had episodic symptoms of confusion, seeing flashlights and shifted vision. OSH EEG reported 11-16 SZs/day from right posterior head region. At OSH this Pt had invasive subdural grids (SDG)-EEG where typical spells were recorded without EEG changes. When referred to us few years later, our EEG showed frequent SREDA from right more than left posterior head regions. None of these patients had interictal epileptiform discharges, and their EEGs were normal except for the expected breach rhythm and focal slowing in the right posterior head region in PT#5 due to prior craniotomy for SDG. None of these Pts had symptoms during SREDA discharges. Their typical episodic symptoms were recorded with normal EEG. Furthermore, there was no findings suggestive of a focal epilepsy in MRI & PET in all pts, MEG done in 4 pts and SPECT done in 3 pts.

Conclusions: The misinterpretation of SREDA as seizures leads to misdiagnosis of (intractable) epilepsy, causes harm by unnecessary treatment with multiple ASMs, and invasive procedures such as device implantation and invasive EEG evaluation. Furthermore, it leads to unnecessary inpatient and outpatient testing, and increases financial burdens to health care system.

Funding: none