Ambiguous paroxysmal events

Epilepsy & Seizures

Updated 03.22.2024
Released 08.15.2014
Expires For CME 03.22.2027

Ambiguous paroxysmal events

Authors: Priyanka Atit DO, Selim R Benbadis MD

See Contributor Disclosures

Editor: Jerome Engel Jr MD PhD

Ambiguous paroxysmal events

In This Article

Quick Link

Initial evaluation

The initial diagnosis of seizure is based on the history. If first-line treatment fails, the diagnosis is (or should be) questioned and verified. At epilepsy centers, where selected challenging patients are seen, the evaluation typically begins with video-EEG monitoring, which allows a clear diagnosis in the vast majority of cases (10; 08). Typically, video-EEG will answer the following questions:

(1) Is it epilepsy or not?
(2) If it is not epilepsy, what is it?
(3) If it is epilepsy, what type?
(4) If seizures are focal, where is the focus?

In this article, we will focus on the first two questions. Is it epilepsy or not? If it is not epilepsy, what is it? In the vast majority of cases, the question of “epilepsy or not” is easily answered, so we will focus on the relatively small proportion of situations in which, despite good EEG or video-EEG recordings, the question remains difficult to answer. We will divide “ambiguous” events into clinical and electrographic events.

Cell phone videos can be particularly helpful at clarifying ambiguous events, and studies have shown excellent diagnostic value (27; 02).

Clinical events

Facial movements. Mouth movements may be misinterpreted as seizure activity because partial seizures often include clonic facial twitching or oral automatisms. Nonepileptic facial movements can represent tics, hemifacial spasm, or other abnormal movements (04). Tics are brief and stereotyped in a given patient, and although they are worse under stress, they tend to occur regularly throughout the day rather than in discrete episodes. Tics are also suppressible by the patient with concentration. However, when suppressed, the urge builds up (like a compulsion), and the tic is eventually produced, triggering a brief feeling of “just right.” Tics may be related to involvement of the basal ganglia and related cortico-striato-thalamo-cortical circuits, and the dopaminergic neuronal system (25).

Ambiguous paroxysmal events: facial movements (1)

Left facial twitching can be misinterpreted as seizure with motor symptoms of the face. This involves the periorbital muscles with bilateral high amplitude, fast frequency myogenic potential at frontopolar electrodes. Movements be...
Ambiguous paroxysmal events: facial movements (2)

Video shows left facial twitching while EEG shows normal background with movement artifacts and frequent eye blinking. Clinically, during activation, there is sudden, brief movement of angle of the mouth with eyes closure. (Contri...

Hemifacial spasm can superficially resemble focal motor seizures, but the unilateral facial twitching typically affects the periorbital muscles initially, rather than the perioral area, and then spreads to other ipsilateral facial muscles over months or years. Unlike seizures, hemifacial spasms are sometimes suppressible by engagement in motor activity and can decrease during sleep (15). Hemifacial spasm is a progressive disorder that eventually results in fixed facial weakness or blepharospasm. It is related to hyperexcitability at the facial nucleus and brainstem structures (23).

Oculomasticatory myorhythmias are rare (though relatively common in Whipple disease) vermicular movements of masticator muscles accompanied by supranuclear gaze paresis or other central ocular manifestations (26).

Eye movements may at times be misinterpreted as seizure activity. Abnormal eye movements, like nystagmoid eye jerks, hippus, repeated blinking, and sustained eye deviation in any direction, are in fact an important clue in suspecting nonconvulsive status epilepticus in encephalopathic patients (18). Various nonepileptic eye movements are also often seen in this setting, eg, abnormal saccadic eye movement in hepatic encephalopathy and ocular bobbing in pontine lesions (20).

Brief isolated jerks. Myoclonus is a sudden, brief, involuntary movement caused by contraction or inhibition of muscle groups. Myoclonus can be epileptic (cortical) or nonepileptic (subcortical). The latter is mostly seen in patients with toxic (eg, medications) or metabolic (eg, uremia, electrolyte abnormalities, or cerebral anoxia) causes. Because they have large homunculus representation, epileptic clonic/myoclonic jerks typically involve distal limbs or the face, whereas nonepileptic myoclonus usually involves muscles with little homuncular representation.

Ambiguous paroxysmal events: Brief isolated jerk

A nonepileptic, entire body jerk typically occurs in transition to stage 1 non-REM sleep, (hypnicjerk). These jerks occur at all ages and can lead to evaluation of seizures, especially when they are unusually violent. In this vide...

For example, myoclonic jerks are frequently seen with cardiac arrest. Postanoxic myoclonus occurs soon after the inciting event and commonly displays EEG abnormalities, which can be epileptiform. Myoclonic jerks can also develop days or weeks after an anoxic injury (when a patient has regained consciousness) and be associated with epileptiform EEG changes as well (17). Postanoxic tonic eyelid openings (PATEO) are slower, tonic eyelid opening movements, which are preceded by EEG ictal activity and considered poor prognostic signs (01).

Hypnic jerks are a physiologic type of myoclonus that commonly occurs in the healthy population during the transition to N1 non-REM sleep. The person will often have the sensation of falling followed by a stereotyped body jerk. This is a benign and common occurrence and is easily identified by video-EEG, with absent EEG correlate associated with the jerk.

Segmental spinal myoclonus is associated with various spinal cord lesions, including neoplastic, infectious, traumatic, and B12 deficiency (28). The context (evidence for myelopathy) makes the diagnosis relatively easy. It may be caused by loss of inhibitory function of dorsal horn interneurons and abnormal hyperactivity of anterior horn cells of the spinal cord. Segmental myoclonus can be brainstem such as palatal myoclonus.

Out of sleep events. Several events can occur during sleep that may be confounding for seizures to family and providers. This includes periodic limb movements of sleep, and NREM and REM related parasomnias. Some differentiating characteristics in favor of seizures are short duration, stereotyped events, and presence of a tongue laceration. Age of onset can also be a clue. For example, NREM parasomnias frequently present in childhood and resolve by adulthood (14).

Limb shaking TIAs. Typically, sustained or transient hypoperfusion to the brain results in negative symptoms such as weakness, numbness, or communication difficulties. Limb shaking TIAs are an unusual phenomenon whereby positive symptoms, ie, involuntary rhythmic, jerky movements of an arm or leg, can occur in the setting of hypoperfusion from carotid stenosis. Episodes can reoccur several times a day with maneuvers that trigger hypoperfusion such as neck extension. In contrast to focal seizures, there is no involvement of the face, eyes, mouth, or Jacksonian march (22; 16).

Amyloid spells or transient focal neurologic episodes. These are brief, recurrent, and stereotyped events that can consist of negative or positive symptoms that can mimic migraines or seizures. These symptoms are thought to result from the irritant effect of hemosiderin on the cortex (12; 16).

Syncope. Syncope is a transient self-limited loss of consciousness due to transient global hypoperfusion and is mistaken for seizures when it is “convulsive.” The tonic or clonic movements are brief (less than 15 seconds) (21). EEG have very low diagnostic yield in evaluating syncope cause. Vasovagal syncope, arrhythmias, carotid hypersensitivity, and aortic stenosis are recognizable causes of syncope, as well as drugs (beta and alpha blockers) and metabolic causes (13).

Pseudosyncope. Pseudosyncope refers to episodes that look like syncope, but are psychogenic. Whatever the cause, syncope results in a predictable sequence of EEG changes when captured on EEG: high-amplitude slowing followed by suppression (29). Thus, a syncope-like event (complete loss of consciousness) with a normal alpha rhythm is diagnostic of psychogenic pseudosyncope. Because most patients with refractory syncope do not undergo video-EEG monitoring, it is likely that pseudosyncope is underdiagnosed and could account for a significant proportion of “syncope of unknown origin” (07).

Pseudosyncope

The patient felt down on left (with normal EEG before), followed by prominent alpha rhythm. Video EEG is crucial in diagnosis of pseudosyncope. (Contributed by Dr. Selim R Benbadis.)

Transient global amnesia. Episodes characteristically involve profound anterograde amnesia for several hours, or even up to a day. There is no loss of consciousness or loss of identity with this, and reoccurrence is not common. By contrast, seizures with loss of awareness are brief (less than an hour) and anterograde amnesia is not persistent after episode resolution (03; 16).

Focal motor seizures without EEG change. Because focal seizures in clear consciousness usually have no surface EEG change, the diagnosis cannot depend on the absence of ictal EEG. Thus, if symptoms are consistent with this type of seizure, semiology becomes more important than ictal EEG. In this situation, the diagnosis is entirely based on semiology (video) and whether the movements are the type seen in epileptic seizures (clonic or tonic).

Simple partial seizure without EEG changes

This patient had aura followed by behavioral arrest, and he developed gesticulated fingers (dystonic) of the right hand. This EEG showed no focal abnormality. Normal EEG is common during simple partial seizure and does not exclude...

Focal seizures with subjective symptoms (auras). These include common epileptic auras such as rising epigastric sensation, déjà-vu, and fear and usually do not show any ictal surface EEG discharge. Because they are also relatively common in patients without epilepsy, these symptoms can only be diagnosed as epileptic if the EEG shows epileptiform discharges or if they evolve into more obvious seizures (the company they keep). Less specific symptoms (cephalic, “indescribable” sensations) are even more difficult to diagnose and, when in doubt, should not lead to a diagnosis of epileptic seizures.

In the ICU setting. Patients often have various movements or behaviors that are not epileptic, but can superficially mimic seizures.

Ambiguous paroxysmal events: posturing

This patient in the intensive care unit developed decorticate response. The patient developed clenched fist and arms flexion. There is loss of corticospinal tract function with intact rubrospinal fibers that receive excitatory pro...
Abnormal movement in ICU

This patient had oscillatory movement of head and lower limbs not associated with EEG changes. The genesis of such movement (in addition to other nonepileptic abnormal movements in the ICU setting) is not clear; they could represe...
Focal seizure in ICU

This patient had left subdural hematoma. EEG showed continuous slow activity in the left fronto-temporal region. He developed recurrent clonic seizures of the right arm with eye and head deviation to right. EEG showed rhythmic del...

Decorticate or decerebrate posturing typically occur in response to noxious stimuli. Decorticate posturing occurs when there has been interruption to the corticospinal pathways above the midbrain. Clinically, the patients will have adduction and slow flexion of the arms, wrists, and fingers in the upper extremities. In the lower extremities, there will be extension, internal rotation, and plantar flexion. Decerebrate posturing occurs with brainstem damage below the level of the red nucleus. Clinically, patients may have extension of the head and trunk (opisthotonus); arms will be adducted, extended, and internally rotated; and legs will be extended and internally rotated, with plantar flexion and inversion of the feet (05).

Tremors or shiver-like movements are relatively frequent in the ICU setting or in patients coming out of general anesthesia. One key to distinguishing tremors is that a tremor is a to-and-fro oscillating movement across a joint. Tremors are not tonic, clonic, or myoclonic in nature.

EEG events

Focal sharp transients

Wickets waves. Wickets waves are 6 to 11 Hz medium- to high-voltage sharp transients in the temporal regions. They do not clearly stand out and arise from ongoing activity of the same frequency. These are, by far, the most common benign waveforms misinterpreted as epileptiform and are often responsible for the erroneous diagnosis of epilepsy (11; 05).

Wicket waves

10 Hz left temporal wicket waves, not followed by slow activity. (Contributed by Selim R Benbadis MD.)

Lambda waves and positive occipital sharp transients of sleep (POSTS). Both are occipital and have a similar morphology. Lambda waves occur during visual scanning, whereas POSTS occur during non-REM sleep.

Lamba waves

Lamba waves in the bilateral occipital region, which occur during visual scanning. (Contributed by Selim R Benbadis MD.)
Positive occipital sharp transients of sleep (POSTS)

POSTS in the bilateral occipital triangle, which occur in non-REM sleep, most commonly stage II. (Contributed by Selim R Benbadis MD.)

Small sharp spikes (SSS). SSS are sporadic unilateral or bilateral temporal spikes that occur during light sleep. They are “small” (< 50 microV) and “sharp” (< 50 msec), and are known as benign epileptiform transient of sleep (BECTS).

Small sharp spikes (SSS)

Small sharp spikes at the left temporal region. Short (<50 ms duration) and low amplitude (< 50 microvolt). (Contributed by Selim R Benbadis MD.)

Subclinical rhythmic electrographic discharge of adults (SREDA). SREDA typically consists of rhythmic theta activity over the posterior temporoparietal region lasting for many seconds to several minutes, but without the evolution typical of focal seizures. This is a pseudoictal pattern.

Subclinical rhythmic electrographic discharge of adults (SREDA)

SREDA typically consists of theta activity over the posterior temporal and parietal region and lasts for many seconds. (Contributed by Selim R Benbadis MD.)

Rhythmic midtemporal theta of drowsiness (RMTD). RMTD, also known as “psychomotor variant,” are 4 to 7 Hz rhythmic discharges, maximum in the midtemporal region, unusually unilateral, and, again, without evolution. The morphology is typically notched, flat-topped, or sharply contoured. Bursts last for 1 to 30 seconds.

Rhythmic midtemporal theta of drowsiness (RMTD)

In this figure, RMTD is unilateral. However, RMTD can be bilateral or independent. (Contributed by Selim R Benbadis MD.)

Breach rhythm. Breach rhythm consists of high-voltage activity over a skull defect and can contain sharp transients that can mimic interictal epileptic discharges. However, they are usually accompanied by a baseline amplitude asymmetry (09).

Breach rhythm

Sharply contoured 7 Hz activity prominent over the left temporal region. This patient has a skull defect over the corresponding area. (Contributed by Selim R Benbadis MD.)

Pseudoictal patterns

Artifacts due to rhythmic movements (voluntary or tremors) are usually easily clarified by review of video.

Ambiguous paroxysmal events: rhythmic movements

Artifact caused by rhythmic movement can be difficult to distinguish from cortical pattern. Psychogenic nonepileptic seizures typically have less variability in frequency within a narrow range of duration. It has been shown that t...

Hyperventilation can produce diffuse slowing during hyperventilation in healthy patients, and this may be prolonged in the context of hypoglycemia or hypoxia. Slowing may persist after the termination of hyperventilation in patients with syncopal episodes. Slowing can rebuild after hyperventilation in Moyamoya disease.

A harmonic of a normal alpha rhythm can occasionally generate a rhythmic discharge that mimics seizures, although there is no evolution. This discharge is identified by the fact that the rhythmic activity is half or twice the alpha frequency.

Ambiguous paroxysmal events: harmony

Frequency of photic stimulation driving can be equivalent to stimulus frequency (f), harmonic driving (nf), and subhormonic driving (f/n), where n is 2 or greater.This driving is not visual evoked potentials that occur with stimul...

Periodic lateralized epileptiform discharges (PLEDs), generalized periodic epileptiform discharges (GPEDs), and other generalized patterns such as triphasic waves are easy to identify and are only “ambiguous” in terms of their significance, ie, ictal, interictal, or nonepileptogenic. PLEDs and GPEDs are EEG discharges, usually epileptiform in appearance, that occur at a relatively constant periodic interval. In most cases, PLEDs are caused by acute focal destructive structural lesions (most commonly stroke). GPEDs can be due to severe metabolic disturbances, including anoxia, and can be indicative of nonconvulsive status epilepticus. In practice, whether a continuous generalized periodic pattern represents status epilepticus will usually require a very careful clinical assessment, CT/MRI, and other investigations (04). PLEDs that evolve or are associated with rhythmic fast, or sometimes rhythmic delta, activities (PLEDS-plus) are strongly associated with clinical seizures and status epilepticus (24).

Media

References

01: Alsallom F, Shaker H, Newey C, Hantus S, Punia V. Characterization of postanoxic tonic eyelid opening: a poorly recognized prognostic sign. Neurol Clin Pract 2021;11(4):e422-29. PMID 34484940
02: Amin U, Nascimento F, Karakis I, Schomer D, Benbadis S. Normal variants and artifacts: importance in EEG interpretation. Epileptic Disord 2023. [Epub ahead of print] PMID 36938895
03: Bartsch T, Butler C. Transient amnesic syndromes. Nat Rev Neurol 2013;9(2):86-97. PMID 23296343
04: Benbadis SR. Differential diagnosis of epilepsy. Continuum Lifelong Learning Neurol 2007;13(4):48-70.
05: Benbadis SR. The tragedy of over-read EEGs and wrong diagnoses of epilepsy. Expert Rev Neurother 2010;10(3):343. PMID 20217964
06: Benbadis SR, Chen S, Melo M. What's shaking in the ICU. The differential diagnosis of seizures in the intensive care setting. Epilepsia 2010;51(11):2338-40. PMID 20738384
07: Benbadis SR, Chichkova R. Psychogenic pseudosyncope: an underestimated and provable diagnosis. Epilepsy Behav 2006;9(1):106-10. PMID 16697264
08: Benbadis SR, LaFrance WC Jr, Papandonatos GD, Korabathina K, Lin K, Kraemer HC; NES Treatment Workshop. Interrater reliability of EEG-video monitoring. Neurology 2009;73(11);843-6. PMID 19752450
09: Benbadis SR, Lin K. Errors in EEG interpretation and misdiagnosis of epilepsy. Which EEG patterns Are overread. Eur Neurol 2008;59(5):267-71. PMID 18264016
10: Benbadis SR, O’Neill E, Tatum WO, Heriaud L. Outcome of prolonged video-EEG monitoring at a typical referral epilepsy center. Epilepsia 2004;45(9):1150-3. PMID 15329081
11: Benbadis SR, Tatum WO. Overintepretation of EEGs and misdiagnosis of epilepsy. J Clin Neurophysiology 2003;20(1):42-4.
12: Charidimou A, Peeters A, Fox Z, et al. Spectrum of transient focal neurological episodes in cerebral amyloid angiopathy: multicentre magnetic resonance imaging cohort study and meta-analysis. Stroke 2012;43(9):2324-30. PMID 22798323
13: Dantas FG, Cavalcanti AP, Rodrigues Maciel BD, et al. The role of EEG in patients with syncope. J Clin Neurophysiol 2012;29(1):55-7. PMID 22353986
14: Derry CP. Sleeping in fits and starts: a practical guide to distinguishing nocturnal epilepsy from sleep disorders. Pract Neurol 2014;14(6):391-8. PMID 24914026
15: Espay AJ, Schmithorst VJ, Szaflarski JP. Chronic isolated hemifacial spasm as a manifestation of epilepsia partialis continua. Epilepsy Behav 2008;12(2):332-6. PMID 17951112
16: Feyissa AM, Bower JH. Evaluation of the patient with paroxysmal spells mimicking epileptic seizures. Neurologist 2022;14(6):391-8. PMID 36223312
17: Gupta HV, Caviness JN. Post-hypoxic myoclonus: current concepts, neurophysiology, and treatment. Tremor Other Hyperkinet Mov (N Y) 2016;6:409. PMID 27708982
18: Husain AM, Horn GJ, Jacobson MP. Non-convulsive status epilepticus: usefulness of clinical features in selecting patients for urgent EEG. J Neurol Neurosurg Psychiatry 2003;74(2):189-91. PMID 12531946
19: Korabathina K, Benbadis SR. EEG diagnosis of nonconvulsive status epilepticus: generalized periodic patterns--status or not. Exp Rev Neurother 2007;7(12):1643-4.
20: Krismer F, Roos JC, Schranz M, et al. Saccadic latency in hepatic encephalopathy: a pilot study. Metabolic Brain Dis 2010;25(3):285-95.
21: Lempert T, Bauer M, Schmidt D. Syncope: a videometric analysis of 56 episodes of transient cerebral hypoxia. Ann Neurol 1994;36(2):233-7. PMID 8053660
22: Nadarajan V, Perry RJ, Johnson J, Werring DJ. Transient ischaemic attacks: mimics and chameleons. Pract Neurol 2014;14(1):23-31. PMID 24453269
23: Oge AE, Yayla V, Demir GA, Eraksoy M. Excitability of facial nucleus and related brain-stem reflexes in hemifacial spasm, post-facial palsy synkinesis and facial myokymia. ClinNeurophysiol 2005;116(7):1542-54.
24: Orta DS, Chiappa KH, Quiroz AZ, Costello DJ, Cole AJ. Prognostic implications of periodic epileptiform discharges. Arch Neurol 2009;66(8):985-91. PMID 19667220
25: Rampello L, Alvano A, Battaglia G, Bruno V, Raffaele R, Nicoletti F. Tic disorders: from pathophysiology to treatment. J Neurol 2006;253(1):1-15. PMID 16331353
26: Schwartz MA, Selhorst JB, Ochs AL, et al. Oculomasticatory myorhythmia: a unique movement disorder occurring in Whipple's disease. Ann Neurol 1986;20:677. PMID 2434019
27: Tatum WO, Hirsch LJ, Gelfand MA, et al. Assessment of the predictive value of outpatient smartphone videos for diagnosis of epileptic seizures. JAMA Neurol 2020;77(5):593-600. PMID 31961382
28: Tsao JW, Cooper EC. Reflex-sensitive spinal segmental myoclonus associated with vitamin B12 deficiency. Neurology 2003;61(6):867-8. PMID 14504348
29: van Dijk JG, Thijs RD, van Zwet E, et al. The semiology of tilt-induced reflex syncope in relation to electroencephalographic changes. Brain 2014;137(Pt 2):576-85. PMID 24343112

Contributors

All contributors' financial relationships have been reviewed and mitigated to ensure that this and every other article is free from commercial bias.

Authors

Priyanka Atit DO

Dr. Atit of University of South Florida has no relevant financial relationships to disclose.
See Profile
Selim R Benbadis MD

Dr. Benbadis of the University of South Florida and Tampa General Hospital received honorariums from Catalyst, Jazz, LivaNova, Neurelis, SK Life Science, Stratus, and UCB as consultant, speaker, or advisory board member. He received grant support from Cerevel Therapeutics, Elsai, Jazz, LivaNova, Longboard, Marinus, Neuropace, SK Life Science, Takeda UCB, and Xenon Pharmaceuticals.
See Profile

Editor

Jerome Engel Jr MD PhD

Dr. Engel of the David Geffen School of Medicine at the University of California, Los Angeles, has no relevant financial relationships to disclose.
See Profile

Former Authors

Fahad Salih Algreeshah MD
Melissa J Freeman MD

This is an article preview.
Start a Free Account
to access the full version.

Nearly 3,000 illustrations, including video clips of neurologic disorders.
Every article is reviewed by our esteemed Editorial Board for accuracy and currency.
Full spectrum of neurology in 1,200 comprehensive articles.
Listen to MedLink on the go with Audio versions of each article.

Questions or Comment?

MedLink®, LLC

3525 Del Mar Heights Rd, Ste 304
San Diego, CA 92130-2122

Toll Free (U.S. + Canada): 800-452-2400

US Number: +1-619-640-4660

Support: service@medlink.com

Editor: editor@medlink.com

ISSN: 2831-9125

Ambiguous paroxysmal events

Associated Disorders

Clonic facial twitching
Decorticate or decerebrate posturing
Epileptic myoclonus
Focal seizures
Nonepileptic facial movements
- Nonconvulsive status epilepticus
- Nonepileptic myoclonus
- Oral automatisms
- Pseudosyncope
- Segmental spinal cord myoclonus
- Syncope
- Tremors

Also Relevant

Blepharospasm
EEG in epilepsy
Hemifacial spasm
Myoclonic seizures
Myoclonus
- Myoclonic status epilepticus
- Nystagmus
- Oromandibular dystonia
- Subtle status epilepticus
- Syncope
- Tremors
- Transient global amnesia
- Parasomnias