EEG Signals in Psychiatry: Biomarkers for Depression Management - Quantitative EEG Analysis Methods and Clinical Applications - page 296

11.2.2.1 Cordance and the ATR Index
Several physiologically based biomarker approaches to predicting outcomes have
emerged in recent years in the area of depression with peer-reviewed publication and
independent replication of findings. These approaches can serve as useful examples
for evaluating a candidate biomarker for clinical use. The first measure uses changes
in resting-state prefrontal brain activity, assessed with qEEG cordance [10] over the
course of a test exposure to an antidepressant medication. This early physiological
change has been found to be predictive of later treatment outcome with that agent
for the individual patient, in studies using either serotonin reuptake inhibitors (SRIs)
or dual-reuptake inhibitor antidepressants [79-83]. Cordance is a measure that
combines features of absolute and relative EEG power. Because cordance is better
correlated with regional cerebral blood flow than other EEG measures [10], findings
with this measure can be interpreted within the same conceptual framework as other
functional neuroimaging studies.
A multisite replication and extension project (NCT00375843) has recently
closed enrollment and data analysis is now under way. The relationship between
early change in cordance and later clinical outcome was independently replicated in
an inpatient sample using a variety of medications [84] and in a second inpatient
sample using only venlafaxine in Level 1 treatment-resistant depression [85]. Using
data from our prior trials [80], a receiver operating characteristic (ROC) curve can
be constructed as an example of the use of an early change in prefrontal cordance as
a predictor of treatment outcome. Using data from the 2-week assessment qEEG
recordings, overall predictive accuracy in differentiating treatment responders from
nonresponders was 84%, with sensitivity of 77% and specificity of 92% (Figure
11.2).
These findings sparked additional research in the use of physiological
biomarkers to advance the possibilities of personalized medicine. An even larger col-
laborative, multisite trial, BRITE-MD (Biomarkers for Rapid Identification of
Treatment Effectiveness in Major Depression, NCT00289523, n = 375), was under-

ROC on frontal cordance change (2 weeks)

Figure 11.2 ROC curve using cordance as a treatment outcome predictor.