# 34 - Abnormalities in EEG

# Abnormalities in EEG

© SPMM Course 
Abnormalities in EEG 
EEG in various disorders 
Absence seizures (petit-mal) 
Regular 3 Hz Complexes 
Alzheimer’s dementia 
Rarely normal in advanced dementia; may be helpful in differentiating 
pseudodementia from dementia 
Angelman’s syndrome 
1. EEG changes are notable by the age of 2. 
2. Prolonged runs of high amplitude 2–3 Hz frontal activity with 
superimposed interictal epileptiform discharges – all ages 
3. 3. Occipital high amplitude rhythmic 4–6 Hz activity facilitated by 
eye closure, is seen under the age of 12 years. 
4. 4. There is no difference in EEG findings in AS patients with or 
without seizures 
Antisocial personality disorder 
Increased incidence of EEG abnormalities in those with aggressive behaviour 
 ADHD 
Up to 60% have EEG abnormalities (spike/spike-waves) 
Borderline personality disorder 
Positive spikes: 14- and 6 per second seen in 25% of patients 
CJD 
Generalised periodic 1-2 Hz sharp waves are seen in nearly 90% patients with 
sporadic CJD. Less often in familial / hormonal transplant-related forms. NOT 
seen in a variant form. 
Closed head injuries 
Focal slowing (sharply focal head trauma) 
Focal delta slowing (subdural hematomas) 
Diffuse atherosclerosis 
Slowed alpha frequency and increased generalized theta slowing 
Herpes simplex encephalitis 
Episodic discharges are recurring every 1-3 seconds with variable focal waves 
over the temporal areas. 
Huntington’s dementia 
Initial loss of alpha; later flattened trace 
Infantile spasms (seen in 
tuberous sclerosis) 
Hypsarrhythmia [diffuse giant waves (high voltage, >400 microvolts) with a 
chaotic background of irregular, asynchronous multifocal spikes and sharp 
waves]. Clinical seizures are associated with a marked suppression of the 
background - called the electrodecremental response 
Infectious disorders 
Diffuse, often synchronous, high voltage slowing (acute phase of encephalitis) 
Metabolic and endocrine 
disorders 
Diffuse generalized slowing. Triphasic waves: 1.5 to 3.0 per second highvoltage slow-waves especially in hepatic encephalopathy. 
Neurosyphilis 
The non-specific increase in slow waves occurring diffusely over the scalp. 
Panic disorder 
Paroxysmal EEG changes consistent with partial seizure activity in one-third; 
focal slowing in about 25% of patients 
Seizures 
Generalized, hemispheric, or focal spike/ spike-wave discharge. 
Stroke 
Focal or regional delta activity 
Structural lesions 
Focal slowing / focal spike activity