The relative usefulness of SEEG and QEEG depends on the clinical indications for testing. Mental status changes, unusual presentations, personality changes, episodic behavior, and attention problems are situations that often prompt testing.Acute or gradual mental status change
Patients with advanced dementia rarely have normal SEEG results, so a normal EEG is important in diagnosing pseudodementia secondary to depression or psychosis. When dementia and depression coexist, it becomes important to assess the relative contribution of each disorder to the overall clinical presentation; and SEEG has been shown to be helpful in this situation.4 SEEG is insensitive to the early stages of dementia, however, and cannot be relied on in diagnosing frontotemporal dementia (FTD).
One reason for SEEG insensitivity to early dementia is that EEG changes in most dementing disorders are exaggerations of those found in normal aging. QEEG controls for healthy aging, however, and is sensitive even to subtle changes beyond normal limits. QEEG detects significant abnormalities at the earliest stages of dementia, which increase in parallel with increasing dementia severity. Figure 1 shows an example of a QEEG obtained from a demented patient. In addition to the more easily identified dementia types, QEEG may facilitate the difficult diagnosis of FTD. Perhaps of more importance, QEEG has been shown to distinguish accurately between dementia and pseudodementia.
The differential diagnosis of acutely disturbed and disorganized demented or psychotic patients often includes delirium. SEEG may be helpful in revealing whether altered consciousness is the result of a diffuse encephalopathic process, a focal brain lesion, or continued epileptic activity without motor manifestations. Usually, delirious patients have a toxic-metabolic encephalopathy with diffuse slowing of the background rhythms. Figure 2 shows an SEEG obtained from an acutely confused patient. Limited published research, however, suggests that QEEG adds little to standard visual analysis for the detection of delirium.Unusual presentation
An atypical clinical presentation is the most important factor for initiating an SEEG evaluation.5 However, patients with a nonatypical rapid-cycling bipolar disorder also may exhibit epileptiform EEG discharges.6 This may explain the reported effectiveness of anticonvulsants for rapid-cycling bipolar disorders.
Himmelhoch7 described the clinical characteristics of subictal mood disorders, including brief euphorias, mixed bipolar episodes, brief severe depressive dips with impulsive suicide attempts, compulsive symptoms, irritability and hostile outbursts, and marked premenstrual worsening. Patients with these disorders may also have paradoxical reactions to lithium(Drug information on lithium) and antidepressants, with better response to anticonvulsants.
QEEG is very sensitive for the detection of depression and for the discrimination between depression and dementia. A limited number of articles in the literature further suggest that QEEG accurately discriminates between unipolar depression and bipolar disorder, but this finding awaits independent replication.Recent personality change
An obvious recent personality change should always be viewed as a danger sign, and a full evaluation should be performed. Chronic postconcussive syndrome deserves special mention. QEEG is more helpful than SEEG in such cases. Even mild concussions in which the patient experiences either no loss of consciousness or less than 20 minutes of unconsciousness can cause reduced attention span, reduced shortterm memory capacity, depression, mood disorders, word-finding problems, and slowness of thought. EEG changes that often accompany mild head injury include reduced beta and/or alpha activity and increased theta activity.8 One commercially available QEEG system is tailored to detect brain damage secondary to closed head injuries and has been demonstrated to do so with greater than 95% accuracy.9Episodic behavior