EEG and Neuroimaging
Core concepts
EEG measures cortical electrical activity. Know the normal rhythms: alpha (8–13 Hz, posterior, eyes closed), beta (>13 Hz, frontal), theta (4–7 Hz), delta (<4 Hz). Interictal epileptiform discharges (IEDs) are spikes, polyspikes, and sharp waves; they support but do not confirm epilepsy. Activation procedures include hyperventilation (absence), photic stimulation, and sleep deprivation.
Patterns to recognize
- 3 Hz generalized spike-and-wave - absence epilepsy.
- Hypsarrhythmia - infantile spasms.
- Centrotemporal spikes - benign rolandic epilepsy.
- Periodic lateralized epileptiform discharges (PLEDs) - acute injury, not necessarily seizures.
- Burst suppression - severe encephalopathy or deep anesthesia.
Neuroimaging
MRI with an epilepsy protocol (thin slices, coronal FLAIR, T1, T2) is preferred over CT. Look for hippocampal sclerosis (atrophy + hyperintensity on T2/FLAIR), focal cortical dysplasia, tumors, vascular malformations, and prior injury. CT is for acute settings (hemorrhage, trauma). PET and SPECT are adjuncts in presurgical evaluation.
Traps
- Treating the EEG, not the patient - IEDs can occur in asymptomatic individuals.
- Assuming a normal routine EEG excludes epilepsy; consider sleep or prolonged EEG.
- Confusing PLEDs with status epilepticus.
Rule of thumb
3 Hz spike-and-wave = absence; hypsarrhythmia = infantile spasms; centrotemporal spikes = rolandic epilepsy.