Triphasic waves in EEG

Triphasic waves , characteristic EEG abnormality, etiology , clinical significance and treatment

1. Triphasic waves in EEG Dr Sandhya Manorenj Associate Professor Neurology , Deccan College of Medical Sciences. 20/12/20

2. Introduction Triphasic waves (TW) are abnormal electroencephalogram (EEG) waveforms seen in association with multiple clinical conditions, including encephalopathy and structural brain lesions, among others. They were initially believed to be pathognomonic of hepatic encephalopathy ; however, they can be seen in any metabolic encephalopathy (in fact, more common with renal than hepatic conditions) and some other conditions. They may be considered a subset of generalized periodic discharges (GPDs). Dr. Sandhya Manorenj

3. Who described ? This EEG pattern was first described by Foley in 1950. It was an EEG recording of a patient with hepatic encephalopathy. The term triphasic waves was first coined in 1955 by  Bickford and Butt , given the three-phase morphology. Dr. Sandhya Manorenj

4. Pathophysiology Triphasic waves are not seen in a normal awake state and only seen in patients with altered levels of consciousness.  It is hypothesized that they occur due to structural or metabolic abnormalities affecting the  thalamocortical relays.  The probable pathogenesis is dysfunction of the oscillatory system between the cortex and thalamus for metabolic encephalopathy. Extensive structural or metabolic injuries of the brain stem, diencephalon, and subcortex may be caused by nonmetabolic factors. Some studies have shown that TWs may be correlated with intracranial hypertension . Dr. Sandhya Manorenj

5. EEG characteristics of Triphasic waves (typical) These waveforms have 3 phases with a total duration of 300 to 600 milliseconds. They are  high amplitude sharply contoured waves, with the duration of each phase longer than the next. The first phase is always negative; the second wave is positive, displaying the highest amplitude (greater than 70 microvolts ), with a third slow negative deflection . The triphasic waves usually repeat periodically at a rate of 0.5 Hz to 2 Hz.  They are seen diffusely with synchronous bifrontal and central predominance and display a fronto-occipital time lag ( > 100 millisec ). Dr. Sandhya Manorenj

6. Dr. Sandhya Manorenj

7. Images of Typical triphasic wave Dr. Sandhya Manorenj

8. EEG characteristic of atypical Triphasic waves A typical ( likely epileptic ) triphasic waves. Atypical features include localization : bifrontal / frontopolar , parietal and temporal predominance in epileptiform triphasic waves Contour : Not a blunt contour Duration : less than 200 milliseconds with epileptiform or atypical triphasic activity. A t ypical triphasic waves not altered by external stimuli (EEG reactivity) and Does not display a fronto-occipital delay Dr. Sandhya Manorenj

9. Difference between typical and atypical triphasic waves Typical Seen in Metabolic encephalopathy (hepatic , renal, toxic . Location: frontocentral. Contour :More blunt contour Duration between 300 to 600 millisec . Atypical Likely epileptogenic (NCSE, structural lesion)  localization bifrontal / frontopolar , parietal and temporal predominance. Contour not blunt. Duration less than 200 millisec   Dr. Sandhya Manorenj

10. Typical Vs atypical triphasic waves (TW) Typical triphasic waves can be altered by external stimuli (EEG reactivity ) Usually display a fronto-occipital delay (>100 millisec ). Usually bilateral and generalized Classic TW is 1.5 to 2.5Hz Not altered by external stimuli No delay or time lag Can be focal and later sec generalized. Dr. Sandhya Manorenj

11. Generalized and focal triphasic waves  A majority of TWs show widespread synchronization . General TWs are considered to be linked with metabolic and toxic encephalopathy, such as hepatic or renal diseases, hyponatremia, hypercalcemia, hyperthyroidism, hyperglycemia , and hypoxic-ischemic encephalopathy.  Focal TWs are present mainly in the frontal region and the occiput .   . Focal or unilateral TWs were found in stroke, viral encephalitis, and dementia. Dr. Sandhya Manorenj

12. Types of triphasic waves( TW) 1 ) Typical and atypical triphasic waves based on EEG characteristics 2 ) triphasic sharp wave (≤ 200 millisec ) and triphasic slow wave (> 200 millisec ) based on duration of 3 phases . 3) Generalized and focal TW based on location of TW. Dr. Sandhya Manorenj

13. Causes of triphasic waves Generalized TW usually in metabolic encephalopathy : associated with slow background and causes are Hepatic encephalopathy, uremic encephalopathy, hyperthyroidism, hypothyroidism,Hypernatremia,Hyponatremia,Hypercalcemia,Hypoglycemia,hyperosmolar state, azotemia . Toxic causes : Pregabalin toxicity, Naproxen, lithium toxicity, Metrizamide , cefipime . Hypoxic ischemic insult Other conditions: Serotonin syndrome,Maple syrup urine disease. Ictal or post ictal state Dr. Sandhya Manorenj

14. Triphasic waves due to structural lesion Usually focal and causes include Cerebral abscess Thalamic gliomas Craniopharyngioma Pontine stroke Cerebral carcinomatosis Multifocal cerebral lymphoma Creutzfeldt-Jakob disease (CJD) Alzheimer and other neurodegenerative diseases Head trauma Subdural hematoma Carcinomatous meningitis Dr. Sandhya Manorenj

15. Triphasic waves ? Periodic discharges in CJD Typical and characteristic EEGs in Creutzfeldt – Jakob disease are bisynchronous periodic waves.  The EEG showed periodic biphasic and triphasic complex sharp waves at 0.5 to 1.5 Hz predominantly in frontotemporal leads. Dr. Sandhya Manorenj

16. Clinical significance of TW Triphasic waves can be used as a guide for treatment in addition to laboratory workup . It is important to identify triphasic waves and differentiate them from normal EEG variants and other abnormal EEG waveforms. The absence of asterixis in a patient with triphasic waveforms must warrant neuroimaging to evaluate for structural abnormalities , which can cause triphasic waves. These waveforms may also be seen in association with subclinical status epilepticus. Dr. Sandhya Manorenj

17. Clinical significance of TW When triphasic waves are present in an individual with acute encephalopathy, it often indicates a more significant impairment and prolonged hospital course. Response to stimulation methods routinely utilized in unresponsive patients like nailbed pressure, etc., must be used when reviewing the EEG tracings as it affects prognosis Non-reactive EEG patterns with triphasic activity in patients presenting with acute encephalopathy are associated with increased odds of mortality .  When patients with severe encephalopathy have generalized periodic discharges (GPDs), a longterm EEG monitoring should be considered at times to exclude seizures.

18. Treatment Typical triphasic waves do not require treatment, but rather treatment must be directed towards the etiology . With hepatic encephalopathy, treatment must be directed towards identifying and treating precipitating factors that cause the hepatic encephalopathy. In addition, medications like lactulose to lower ammonia are important as it draws the ammonia into the colon and promotes excretion . Metabolic correction : electrolyte imbalance, sugar control , azotemia correction. If its epileptogenic triphasic / atypical TW, then AEDS indicated.

19. References https://www.ncbi.nlm.nih.gov/books/NBK557679/ . EEG Triphasic waves. Liu, Chang ; Cheng, Shihuan ; Ma, Yue ; Liu, Caiyun ; Lv , Yudan.Triphasic waves in electroencephalogram as a possible early marker of carcinomatous meningitis: a case report.Medicine : August 14, 2020 - Volume 99 - Issue 33 - p e21735. Adriana Bermeo-Ovalle.Triphasic Waves: Swinging the Pendulum Back in this DiagnosticDilemma.https ://www.ncbi.nlm.nih.gov/pmc/articles/PMC5340556/pdf/i1535-7511-17-1-40.pdf