This EEG report describes various types of muscle artifacts that can appear on an EEG. A 47-year-old male presented with a severe headache and was found to have a subarachnoid hemorrhage. The EEG showed chewing artifact and generalized slow activity. The report then discusses different types of muscle artifacts including those from the lateral rectus, frontalis, temporalis muscles and from swallowing, sniffling, palatal myoclonus, facial myokemia and tremors. Methods to reduce artifacts by relaxing muscles or changing electrode positions are also described.

1. Unknown EEG Conference
Mohamed Nasser, M.D
10/11/2016

3. EEG Description
• Montage: M5
• Age: Adult
• Patient state of consciousness: Awake
• EEG Findings: Chewing artifact
• EEG Classification: Abnormal III
• EEG abnormalities: Continuous slow, generalized

4. PMH:
• 47 yo male presented with “worst headache of his life.”
• PMH and PSH: type II Diabetes Mellitus, L- frontal craniotomy,
orbital osteotomy, left frontal ventriculostomy and A-comm
aneurysm clipping.
• CT head : diffuse SAH and third ventricle IVH.
• EEG to evaluate for encephalopathy.

5. Muscle Artifacts

6. Introduction:
• The EEG –highly sensitive recording device, easily interrupted by
other electrical activity arising from different resources, other than
cerebral activity, ‘EEG artifacts’.
• Some readily distinguished, other closely resemble cerebral activity.

7. Classification:
Physiological artifacts
From patient’s own physiological generator sources other than the
brain e.g. Eye movement, cardiogenic, skin artifacts and muscle
activity.
Non-physiological artifacts
Externally generated e.g. instrumental & environmental.

8. Muscle (EMG) artifacts
• EMG artifacts are due to the muscle contraction superimposed upon
the EEG activity.
• The motor unit potentials (MUPs) arising from the scalp muscles may
cause misinterpretation by resembling spike or cortical β-activity.
• Large body movements produce erratic, high amplitude, and rhythmic
waveforms that can usually be readily identified as artifictual.
• Most of EMG potential spectrum lies between 30-150 Hz and are
spiky of extremely short duration 2-20 msec even on increasing paper
speed to 60 mm/sec.

9. Differentiation between EMG artifacts & the
cortical spikes
• On the basis of morphology, frequency and duration.
• EMG activity is reduced during sleep whereas cortical spikes increase.
• Document using extra muscle electrodes. E.g. cheek electrode to
discriminate glossokinetic artifacts.
• Fz, Cz, Pz can give a relatively pure EEG signal.

10. Myoclonic jerk during sleep M4 Montage

11. EMG artifact types
• Lateral rectus spike
• Frontalis
• Temporalis
• Glossokinetic artifact
• Swallowing artifacts
• Palatal myoclonus
• Snuffling artifacts
• Facial Myokemia
• Tremor

12. Lateral rectus spike
• EEG sometimes includes a single MUP from contraction of the lateral
rectus muscle.
• This low amplitude transient is termed lateral rectus spike and is
usually present at F7 (left gaze) and F8 electrode (right gaze).
• May be followed immediately by slower eye movement artifact in the
same location and this may appear as one wave with a morphology
that resembles a focal IED.

13. Lateral rectus spike

14. Frontalis
• Large tense frontal electrode pick up.
• Extremely common especially in elderly, occurring upon squinting or
raising the forehead.
Temporalis
• Most commonly F7, F8, T7, T8, P7, P8.
• Extremely common, upon clenching and grinding teeth. In addition to
chewing.

15. Frontalis

16. Temporalis

17. Glossokinetic artifacts
• The tongue’s tip is electronegative compared to its body. Thus moving
the tongue toward or away from the EEG electrode alter the overall
electrical field around them.
• Movement of the tongue during speaking may produce generalized or
temporofrontal synchronous rhythmic EEG activity of 2-6 Hz.
• These periodic bursts of diffuse delta slow wave may resemble
intermittent generalized, temporal slow activity, FRIDA or even
electrographic seizure discharges.

18. Glossokinetic artifacts

19. Swallowing artifact
This is partly EMG artifact from the pharyngeal muscles and partly
due to the tongue’s inherent dipole.

20. The swallowing Triad: ( Initial spike-like discharge due to dissimilar
metals in teeth followed by glossokinetic potential and temporal
muscle activity)

21. (Swallowing of saliva usually produces a short burst activity)

22. Sniffling artifact (Small EMG component with a slow wave)

23. Palatal myoclonus
• Periodic pattern usually at the rate of 60-120 beat/min which consists
of brief myogenic contractions.
• It is caused by intracranial disorders involving brainstem-cerebellar
circuits ( the dentate olivary pathway).
• Patient is usually unaware of these movements, and the condition is
sometimes first detected in the EEG.
• Visible almost exclusively in recordings with ear lead derivations and
is most evident in an inter-ear lead derivation (A1-A2).
• In some patients each myogenic contraction maybe followed by
evoked cerebral response in the vertex region.

24. Palatal myoclonus

25. Facial myokemia
• Myokemia is an involuntary, spontaneous, localized quivering of a few
muscles, or bundles within a muscle.
• Often associated with brain stem lesions or lesions involving the facial
nerve intracranially causing no other EEG signs.
• Appears on EEG as Pseudoperiodic unilateral pattern of short bursts
of 30-70 Hz muscle potentials with interval between bursts of 1-5 sec.
usually lasts less than 1 sec.
• Visible facial myokemia is usually recorded in FP1 FP2, and sometimes
recorded in temporal electrodes without visible signs when the
vestigial auricularis muscles ,which are innervated by the facial nerve,
are involved.

26. Facial myokemia

27. Tremor
• Patients with a resting tremor due to parkinsonism often have a
characteristic artifact from the associated head movements and that
is particularly prone to occur in an electrode pressing against a
reclining chair or bed.
• Consist of rhythmic 4-7 Hz waves in the occipital leads.

28. Tremor

29. Reduction/Elimination
•Frontalis -turning down the lights
-calming the patient
-un wrinkling their forehead somehow
-massaging the electrode site.
•Occipitalis -propping the patient’s head away from the chair or bed
-use comfortable pillow.
•Temporalis -massaging temporal muscles
-relax the jaw & open mouth slightly.
As a last resort change the high frequency filter to 35/15 Hz.

30. References
• Lüders Textbook of epilepsy sugery
• Devereaux, Modified from Klem, G. Current Practice of Clinical Electroencephalography 2003
• Artifact and Recording Concepts in EEG William O. Tatum,* Barbara A. Dworetzky,† and Donald L. Schomer† 2011
• Espinosa et al. 1967
• Franklin 1972
• Westmore et al 1973

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