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In-Depth Information
EEG is one of the major techniques used to diagnose CJD and has been included
in the World Heath Organization diagnostic classification criteria [24]. In general,
EEG patterns of sCJD exhibit longitudinal changes along with the course of the
disease, ranging from frontal intermittent rhythmical delta activity (FIRDA), i.e.,
slow waves with 1-3 Hz, in the early stage to periodic lateralized epileptiform dis-
charges (PLEDs) or prototypical periodic sharp wave complexes (PSWCs) in the
middle and late stages [1, 3, 6, 25]. The temporal waveforms and the spatial domi-
nances of FIRDA, PLEDs, and PSWCs are presented in the Fig. 4.1a, b, respectively.
The morphology of PLEDs shows complexes which consist of a bi- or multiphasic
spike or sharp wave and may include a slow wave [5]. The PSWCs mainly com-
prise simple sharp waves, i.e., monophasic, biphasic, and triphasic waves, with a
typical duration of 200-600 ms, although complexes with mixed spikes, polyspikes,
and slower waves may appear from times to times [5, 25, 24]. The peak-to-peak in-
tervals of PSWCs are usually between 0.5 and 2 s. The major difference between
the PLEDs and the PSWCs is their topographical dominances. The former is more
hemispherically lateralized while the latter is more focal in the early stage and be-
comes diffusive after the middle stage. Since the PSWCs are not evident until the
middle or late stage, detection of the PSWCs predecessors, such as FIRDA, PLEDs,
and focal tirphasic waves, hidden in the smeared EEG signals is critical for the early
diagnosis.
Fig. 4.1: (
a
) Temporal waveforms of FIRDA, PLEDs, and PSWCs. The PLEDs
mainly consist of a bi- or multiphasic spike or sharp wave. The PSWCs mainly
comprise simple sharp waves, i.e., monophasic, biphasic, and triphasic waves, with
a typical duration of 200-600 ms and the peak-to-peak intervals are usually between
0.5 and 2 s. (
b
) Spatial dominances of FIRDA, PLEDs, and PSWCs. The FIRDA is
usually observed in the frontal areas, the PLEDs are hemispherically lateralized, and
the PSWCs are usually more focal in early stage and become diffusive after middle
stage. (
c
) The whole scalp of each subject was covered with 19 EEG electrodes
placed onto anatomical locations according to the international 10-20 system, where
Fp, F, C, P, O, and T represent the abbreviations of frontal polar, frontal, central,
parietal, occipital, and temporal, respectively. b1: frontal dominant, b2: left-side
lateralization, b3: right-side lateralization, b4: generalized distribution, ID: interval
duration, D: duration, 0.5 s
<
ID
<
2s,D
<
600 ms, typical triphasic wave.
