Practical Guide for Clinical Neurophysiologic Testing: EEG

623 Pages·2009·202.68 MB·English

by  Thoru Yamada

DIFFUSE ENCEPHALOPATHIES ASSOCIATED WITH RELATIVELY
SPECIFIC OR CHARACTERISTIC EEG PATTERNS
EEG is a sensitive and reliable test to evaluate the severity of cerebral dysfunction and to assess the
progress of a disease process. However, most of the EEG abnormalities reflecting diffuse cerebral
dysfunction are nonspecific and do not lead to a specific diagnosis. Nonetheless, there are several
conditions in which EEG shows a relatively specific or diagnostic pattern. Here, only those conditions
and also relatively common diseases requested for EEG evaluation are described in some detail. EEG
findings in other remaining conditions are listed in Table 11-1 with reference citations.
HEPATIC ENCEPHALOPATHY
In the early stage of hepatic encephalopathy, EEG shows slowing of alpha rhythm, which is gradually
replaced by theta and delta waves as the disease progresses. In the somnolent or mildly stuporous
state, EEG often shows triphasic waves (see Fig. 11-11).37 This is characterized by a small negative
wave followed by a prominent positive sharp wave and subsequent broad negative wave. It appears as
a “blunt spike wave” in some cases and may be difficult to differentiate from the EEG of absence
status or nonconvulsive status epilepticus. Finding a well-defined spike among the sharp and wave
complexes indicates epileptiform activity rather than triphasic waves of encephalopathy.
Triphasic waves in hepatic encephalopathy typically occur in a serial, rhythmic fashion at 2 to 4 Hz
with bilaterally synchronous and symmetric distribution. They are usually frontally dominant and
show a phase lag from anterior to posterior head regions.38 While these typical triphasic waves are
common in hepatic encephalopathy, atypical triphasic waves that have a more irregular waveform and
more sporadic occurrence can be seen in other metabolic encephalopathies including uremia,
hyperthyroidism, hypercalcemia, hyponatremia, hypoglycemia, and lithium intoxication.
waves usually disappear with deepening of the coma state. Despite the paroxysmal appearance of
triphasic waves associated with hepatic coma, a complication of clinical seizures is not common. This
is in contrast to triphasic waves of uremic encephalopathy in which seizure is a more common
complication. No single biochemical abnormalities correlate well with the degree of encephalopathy
or EEG alteration, although the role of hyperammonemia has been proposed.40 In the state of
profound coma when EEG is dominated by delta activity, there may be 14-and 6-Hz positive spike
bursts presenting peculiar combinations of slow and fast activities.41 Similar features have been
reported in Reye’s syndrome.42
REYE’S SYNDROME
This syndrome was a prevalent childhood encephalopathy in the early 1970s but dramatically
decreased after avoidance of the use of aspirin for acute febrile illness in children. Despite severe
hepatic dysfunction, triphasic waves are not common. The degree of EEG abnormalities varies
corresponding to the severity of illness, ranging from minimal slowing of background activity to low-
voltage nonreactive delta or burst suppression pattern. Poor prognosis is predicted when EEG shows
low-voltage delta or burst suppression pattern.43 Interestingly, a high incidence of 14-and 6-Hz
positive spike bursts (see “14-and 6-Hz Positive Spike Bursts,” Chapter 13; see also Figs. 13-1
observed during coma associated with an EEG of dominant delta activity (Fig. 11-16
if this represents preservation or precipitation of normal sleep pattern for children and adolescence
during an acute illness. The 14-and 6-Hz positive spikes have also been reported in coma with other
childhood encephalopathies,44 though not as prevalent as seen in Reye’s syndrome.
Slowing Paroxysmal Discharges

I. METABOLIC DISORDERS
Hypoglycemia ++ (D) ++ (D) Spk
Hyperglycemia (nonketotic) + (D) + (F) Spk
Hepatic encephalopathy ++ (D) ++ Triphasic
Uremic encephalopathy, Acute +(D) + (D) Spk, Triphasic waves
Uremic encephalopathy, Chronic +/− (D) + (D) Spk,
Photoparoxysmal response
Hypocalcemia (hypoparathyroidism) ++ (D) ++ (D) Spk
Hypercalcemia (hyperparathyroidism) + (D) –
Hyponatremic (water intoxication) ++ (D) +/−

II. VITAMIN DEFICIENCIES
+/− (D) ++ (D) Spk
Vitamin B (pyridoxine) deficiency
6
Vitamin B (Wernicke’s encephalopathy) + (D) –
1
Vitamin B (pernicious anemia) ++ (D) ++ (D, F) Spk
12

III. ENDOCRINE DISEASES
Adrenocortical insufficiency (Addison’s + (D) –
disease)
Adrenocortical Hyperfunction Fast –
activity↑
Hypopituitarism (Sheehan’s syndrome) + (D) –
Hyperthyroidism Fast +
activity↑
Thyrotoxicosis Fast + (D) Triphasic wave
activity↑
Hypothyroidism (myxedema) + (D) + (D) Spk
Acute porphyria + (D, F) + (D, F) Spk

IV. DEGENERATIVE DISORDERS
Tay-Sachs disease + (D) ++ (D) Spk, Myoclonus
Cherry red spot myoclonus syndrome +/− (D) ++ Positive spike at vertex),
Myoclonus
Gaucher’s disease +/− (D) ++ (D) Photoparoxysmal
response
Globoid leukodystrophy (Krabbe’s disease) + (D) + Hypsarrhythmia
Metachromatic leukodystrophy +/− (D) –
Adrenoleukodystrophy + (D) –
Zellweger’s syndrome + (D) + Spk
MELAS syndrome (Mitochondrial Myopathy + (D) + (F) Spk, PLEDs
Encephalopathy Lactic Acidosis and Stroke)
MERRF syndrome (Myoclonus with Epilepsy +/− (D) + (D)
and Ragged Red Fibers)
PKU (Phenylketonuria) + (D) + (D) Hypsarrhythmia
Batten’s disease (Neuronal ceroid ++ (D) ++ (D) Spk by low-
lipofuscinosis) frequency photic stimulation
Hallervorden-Spatz Disease + (D) + (F, D) Delta/Theta/Spk
Infantile Neuroaxonal dystrophy (Seitelberger’s Fast +/− (D) Theta, Delt
disease) activity
Wilson’s disease (Hepatolenticular degenerative + (D) +/− (D) Delta/Theta/Sharp
disease) wave
Menke’s disease (Kinky-hair disease) + (D) + (F) Spk, Hypsarrhythmia
Tourette syndrome +/− (D) +/− (D, F) Central Sp
Lafora disease + (D) ++ (D, F) Spk,
Photoparoxysmal response,
Myoclonus
Baltic myoclonic epilepsy (Unverricht- + (D) ++ (D) Photoparoxysmal
Lundborg type) response
Alper’s disease +/− ++ (F, D)
Tuberous sclerosis + (D, F) ++ (F, D) Hypsarrhythmia
Sturge-Weber syndrome + (F) + (F) Spk, Hypsarrhythmia
Down’s syndrome +/− +/−
Hereditary optic nerve Atrophy (Leber’s +/− –
disease)
Myotonic dystrophy + (D) –
Congenital muscular dystrophy (Fukuyama + (D) + (D)
type)
Angelman syndrome (Happy puppet syndrome) ++ (D) + (D) Spk
Rett syndrome + (D) ++ (F) Spk, Central spk,
Lennox-Gastaut syndrome

V. INFLAMMATORY/INFECTIOUS
DISEASE
Acute purulent meningitis ++ (D) + (D)
Infectious mononucleosis + (D) +/− (D)
Aseptic meningitis +/− –
Encephalitis ++ (D) + (D)
Herpes encephalitis ++ (F) ++ (F) PLEDs
Rasmussen’s encephalitis + (F) ++ (F)
Congenital rubella encephalitis ++ (D) + (D)
Progressive rubella panencephalitis + (D) + (D) Periodic discharges,
Myoclonus
Congenital Cytomegalovirus disease + (D, F) –
West Nile virus + (D) –
Rabies + (D) –
Rickettsial infections + (D, F) + (D, F)
Lyme disease + (D) –
Fungal disease + (D, F) –
AIDS (Acquired Immune Deficiency + (D, F) + (D)
Syndrome)
Cysticercosis + (D, F) + (F)
Echinococcosis + (D, F) + (D)
Toxoplasmosis + (D) + (D) Hypsarrhythmia
African trypanosomiasis (sleeping sickness) + (D) + (D)
Malaria + (D) +/−
Sydenham’s chorea + (D) +/−
Neuro-Bechets disease (uveomeningitis) + (D) + (D)
Neurosyphilis + (D, F) + (F)
Hemiconvulsions, hemiplegia, and Epilepsy + (F) + (F) Spk, SW
(HHE syndrome)
Brain Abscess ++ + (F,D) PLEDs
(F/D)

VI. DEMENTIA
Alzheimer’s disease + (D) +/− riphasic
Pick’s disease (frontotemporal dementia) – –
Parkinson’s disease + (D) –
Progressive supranuclear palsy +/− (D) + FIRDA
Dementia with Lewy Bodies + (D) + FIRDA
Huntington’s chorea +/− low –
voltage
Normal pressure hydrocephalus +/− (D) + (D) Slow wave bursts
Depression – –
Creutzfeld–Jakob Disease ++ (D) ++ (D) Periodic triphasic
waves

VII. OTHERS
Multiple sclerosis +/1 (D, +/− (D, F)
F)
Reye’s syndrome ++ (D) + 14-and 6-Hz positive
spikes
Subacute sclerosing panencephalitis (SSPE) + ++ (D) Periodic burst
++, prominent, frequent, high incidence; +, often present; +/− may or may not
low incidence; – most often not present or none; D, diffuse; F, focal; Spk, spike or spike-
wave; SW, spike and wave; FIRDA, Frontal intermittent rhythmic delta activity; PLEDs,
Periodic lateralized epileptiform discharges; ↑, increase.
TABLE 11-1 Slowing and/or Paroxysmal Discharge in Different Cerebral Disorders
UREMIC ENCEPHALOPATHY AND RELATED CONDITIONS
In the early stage of uremic encephalopathy, slowing of alpha rhythm and intermittent diffuse theta
bursts appear. As the disease progresses, further slowing of background activity is associated with
increased delta waves and occasionally with intermittent triphasic waves. The triphasic waves seen
in uremic encephalopathy tend to be less rhythmic and more irregular than those seen in hepatic
encephalopathy (see Fig. 11-12 and compare with Fig. 11-11). Intermittent photic stimulation may
induce photomyogenic or photoparoxysmal responses.45 In some, bursts of spike wave or polyspike
wave may be seen with or without seizures. Seizures are seen in more than 30% of patients with