Case Study

A 58 year old male with hypertension and hypercholesterolemia 8 months prior to hospitalization experienced 2 episodes of lightheadedness 2 weeks prior to awakening with a feeling that "everything was spinning". The sensation increased with head movement with concomitant nausea and sweating. He was awake, conversant, and oriented. In the ED he was told of vertigo but was admitted due to concerns of stroke. Cardiology found no significant concerns for active cardiac disease. A CT brain was normal and an MRI was without acute ischemic changes. Laboratory testing was unrevealing. His symptoms resolved several hours following admission. An EEG was performed and was interpreted as abnormal due to "generalized spike and wave". He was discharged with a diagnosis of "seizure disorder" and placed on carbamazepine (CBZ) and instructed not to drive a car. He developed persistent nausea and stomach upset and stopped CBZ 2-3 months later. He presented for another opinion and desires to drive.

092011-clinic2.jpg

Figure: EEG with bilateral myogenic artifact created by movement of the muscles of mastication (presumed chewing). Note brief "spikes" and polyphasic artifact followed by an apparent "slow wave" at 1.5-2Hz. Parameters: longitudinal bipolar montage; sensitivity 7 uv; filters 1-70 Hz.

What was wrong with the patient?

Artifact can mimic almost any type of electrocerebral activity on the EEG1. Biologic artifacts arising from the patient are contained in essentially every routine study. Myogenic artifact may be generated by the frontalis but also by the temporalis and muscles of mastication. The bitemporal location and polyphasic myogenic potentials are produced by contraction of the masseter muscles moving the jaw and with tongue movement during chewing to produce a direct DC potential that may mimic slow waves2 in our patient were misinterpreted as generalized spike-and-wave discharges. Behavioral description by the technologist and video were unavailable to disclose the artifact. The patient's symptoms were ultimately felt to reflect a peripheral vestibulopathy. While GSW may occur as an inherited trait, CBZ might trigger seizures and would be a poor choice of AED. The outside ambulatory EEG was eventually obtained and is depicted above and found to demonstrate misinterpreted artifact. Following his misdiagnosis the patient was able to work part-time, lost income, and did not drive for 8 months.

References

  1. Klass DW. The continuing challenge of artifacts in the EEG. Am J EEG Technol 1995;35(4):239-269.
  2. Tatum WO, Dworetzky B, Schomer D. Artifact and Recording Concepts in EEG. J Clin Neurophysiol 2011;28(3):252-263.
Authored By: 
William O. Tatum DO
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Authored Date: 
09/2011