Focus on Diagnosis: Electroencephalography: A Primer

Abstract

1. Kamakshya P. Patra, MD* 2. Donald W. Lewis, MD† 1. *Children's Hospital of Shreveport, Louisiana State University Health Sciences Center, Shreveport, LA; currently affiliated with the Department of Pediatrics, Mayo Clinic, Rochester, MN. 2. †Division of Pediatric Neurology, Children's Hospital of the King's Daughters, Norfolk, VA. Electroencephalography is the recording of electrical activity along the scalp produced by the firing of neurons within the brain. The first recordings were made by Hans Berger in 1929. EEG activity is due to charge movement across neuronal membranes. This activity reflects the summation of excitatory and inhibitory postsynaptic potentials in apical dendrites of pyramidal neurons of the cortex. EEG tracings can serve many functions: 1. To differentiate epileptic seizures from pseudoseizures, syncope, behavioral disorders, movement disorders, and migraine variants; 2. To distinguish organic or metabolic encephalopathy from primary psychiatric syndromes; 3. To define seizure semiology, prognostication, and characterization for treatment; 4. To localize the epileptic focus for possible respective surgery; 5. To monitor status epilepticus (especially nonconvulsive) in ICUs; 6. To determine whether to wean antiepileptic drugs; 7. To make the diagnosis of brain death; and 8. To investigate parasomnias (sleep disorders). Twenty-one electrodes are usually placed on specific positions on the scalp to measure voltage fluctuations over time. The manner in which pairs of electrodes are connected to each amplifier of the EEG machine is called a montage. Primary generalized epilepsy is suggested by spike-and-wave discharges that are spread widely over both hemispheres of the brain. Spikes and sharp waves in a local area of the brain, such as the left temporal lobe, indicate that partial seizures are beginning in that area. A 6-year-old girl is brought to you by her mother, because her teacher has observed multiple daily staring episodes in which the child is unresponsive to verbal and tactile cues. These episodes last ∼10 to 15 seconds and occur ∼10 to 20 times a day. Immediately after the episode, she resumes normal activity with …