Current Case: Fall 2024
Contributed by: Paul Wilkerson, DO; Meriem Bensalem-Owen, MD, FACNS
Case Presentation
A 53-year-old woman with drug resistant epilepsy (DRE) requiring polytherapy and management with a vagus nerve stimulator (VNS) and a deep brain stimulator (DBS) was admitted due to altered mental status.
The initial EEG was concerning for recurrent focal subclinical electrographic seizures (Figure 1) arising over the temporal electrodes, greater over F7-T7-P7 followed by F8-T8-P8. The EEG onset was characterized by rhythmic 9 Hz alpha waves that evolved to higher amplitude 6 Hz theta waves that spread to adjacent electrodes. Intermittent excessive muscle artifact masked partially some of the EEG. These findings prompted initiation of video-EEG monitoring while the patient’s home medications were optimized. Lorazepam was administered as well as fosphenytoin which had no effect on this recurrent EEG pattern (Figure 2a and 2b). The patient required subsequent mechanical ventilation. A burst suppression pattern was eventually observed on the EEG due to the use of anesthetics. None of these medications altered the electrographic pattern that was interpreted as very frequent recurrent seizures lasting about 1 minute and occurring every 5 minutes. As treatment was being escalated, the patient’s primary epileptologist was consulted.
Question 1: Based the patient’s history and EEG findings, what is the most likely diagnosis?
- Cyclic sub-clinical seizures
- A benign variant
- Artifact
- Focal subclinical status epilepticus
Answer: (click here)
Correct answer: C. Artifact
As treatment was being escalated, the patient’s primary epileptologist was consulted. The review of the video-EEG monitoring showed an unusual field and lack of evolution in morphology and frequency of this cyclic activity once it reached 6 Hz (Figure 2c and 2d). A perfectly cyclic pattern was recognized corresponding to the DBS stimulation cycle (1 minute on and 5 minutes off).
Question 2: What is the next most appropriate step?
- Initiate pentobarbital
- Consult neurosurgery for emergent epilepsy surgery
- Obtain an LP and treat empirically for autoimmune epilepsy
- Turn off the DBS
Answer: (click here)
Correct answer: D. Turn off the DBS.
As the DBS was turned off, the pattern subsided during that time. The current of the DBS left lead was turned back on and the pattern recurred on the EEG involving the left hemispheric electrodes (Figure 3). A similar electrographic pattern emerged when the current was turned back on the right lead. Following these findings, the patient’s management was changed accordingly.
The use of Deep Brain Stimulation (DBS) has expanded from the treatment of movement disorders to the treatment of drug resistant focal epilepsy (DRE) in adults. The DBS stimulation settings used for movement disorders are different from those used for epilepsy in addition to using different thalamic targets for the leads. DBS therapy can cause a distinct artifact on the electroencephalogram (EEG) resulting from the electrical stimulation. Certain EEG artifacts are important contributors to misdiagnosis and it is therefore essential to correctly identify physiologic and non-physiologic artifacts (1,2). DBS tends to cause a distinctive artifact with usually a monomorphic appearance that is the result of the electrical nature of the stimulation (2). Baldwin and colleagues described 3 cases of an usually slow frequency and rhythmic artifact in patients receiving DBS therapy (4). Our case illustrates an unusual EEG artifact in a DRE patient with altered mental status that was initially interpreted as cyclic seizures.
When interpreting EEGs, it is essential to recognize artifact to prevent misinterpretation and unnecessary treatment that may adversely impact patient care and outcome. Some artifacts can cause a substantial challenge to experienced electroencephalographers. The recognition of unusual neurostimulation device artifacts, such as DBS artifact, especially in patients with altered mental status as exemplified in this case, can create a management conundrum.
References:
- Mathias SV, Bensalem-Owen M. Artifacts That Can Be Misinterpreted as Interictal Discharges. J Clin Neurophysiol. 2019 Jul;36(4):264-274.
- McKay JH, Tatum WO. Artifact Mimicking Ictal Epileptiform Activity in EEG. J Clin Neurophysiol. 2019 Jul;36(4):275-288.
- Nascimento FA, Chu J, Fussner S, Krishnan V, et al. Neurostimulation EEG artifacts: VNS, RNS, and DBS. Arq Neuropsiquiatr. 2021 Aug;79(8):752-753.
- Baldwin M, Palka S, Leppla D, et al. Unusual EEG Artifact in Patients with DBS. Clinical EEG and Neuroscience. 2022;53(6):558-561.
