Video-EEG monitoring is the most vital tool used to detect epileptogenic zones. In addition to allowing the examination of the ictal EEGs of the patients, it also helps to determine the lateralizing and localizing features by providing the advantage of examining the seizure semiologies in detail. Although it is known that the figure 4 sign also has a lateralization significance, there are few studies regarding this subject. A study conducted by examining 149 secondary generalized tonic–clonic seizures of 80 patients showed that the epileptogenic focus was contralateral in 96.7% of the cases [100% in extratemporal lobe epilepsy (ETLE), 94.8% in temporal lobe epilepsy (TLE)] with a figure 4 sign [3]. In the same study, the rate of performing correct lateralization with this finding alone was found to be 58.4%. Bleasel et al., who defined the figure 4 sign for the first time, found the rate of showing a contralateral relationship with the seizure focus as 90.9% in TLE and 87.5% in ETLE. Besides, they claimed in their study that although the figure 4 sign is less common than the versive head deviation, the rate of correct lateralization is higher [4]. In another study conducted, it was reported that the figure 4 sign has a high lateralizing significance of 90% in the contralateral hemisphere. This study also stated that the figure 4 sign occurred at the beginning of the tonic phase of the secondary generalized tonic–clonic seizure. However, the authors emphasized that in some seizures, the extension may occur first in one arm and then in the other arm and that the figure 4 sign can be seen on different sides consecutively. This may lead to confusion in detecting the epileptogenic zone. In the article, it is recommended to consider the figure 4 sign that first appears during the seizure. Besides, it is recommended that patients with generalized seizures should be carefully examined for the figure 4 sign, in case TLE and primary generalized epilepsies rarely coexist [1].
Considering the duration of figure 4 in TLE and ETLE patients, it was observed that the duration was longer in ETLE patients, although there was no statistically significant difference in the study conducted by Kotagal and colleagues [1]. In our study, when the duration of the figure 4 sign was examined according to frontal, temporal, and other lobe seizures, no statistically significant difference was found. However, when the duration was examined by gender in our study, it was found that the figure 4 sign lasted longer in the male gender, and this was statistically significant.
It is known that the figure 4 sign typically occurs in supplementary motor area (SMA) seizures and can also be created by electrical stimulation of SMA. In ictal SPECT studies conducted, it was shown that there is hyperperfusion in the primary and supplementary motor areas and basal ganglia in frontal lobe seizures [5,6,7]. However, we know that frontal lobe seizures spread very rapidly, and sometimes the scalp VEM cannot provide enough information for clear epileptogenic focus detection. In this case, invasive VEM and SPECT may be more guiding.
In a study published in 2016, ictal motor signs observed in 236 patients with focal-onset secondary generalized tonic–clonic seizures were examined, and a positive predictive value was calculated for each motor sign. Unilateral tonic posture, versive head deviation, M2e posture, unilateral clonic seizure, asymmetric end clonic jerk, Todd’s paralysis were determined as reliable motor signs with a positive predictive value of more than 80% and strong lateralizing significance. Since figure 4 sign (PPD: 74%) and hand dystonia (PPD: 67%) have a positive predictive value below 80%, they were not included among the reliable motor signs with strong lateralizing value [8].
As in figure 4, the versive head deviation, unilateral tonic posture, Todd’s paresis, focal clonic jerks in the upper extremity also indicate the contralateral focus [2, 8, 9]. In particular, the figure 4 sign can occur with or after the versive head and eye deviation, and it is usually on the same side. The version occurring 10 s before motor generalization indicates a contralateral hemisphere more than 90%. Combining two or more of the classical motor signs almost completely lateralizes the epileptic zone [8]. In our study, in 5 patients for whom figure 4 sign was observed, a versive head deviation was also observed and contributed to the detection of lateralization. In our study, these patients who had both figure 4 signs and versive head deviation were temporal lobe epilepsy, and two of them underwent surgery for mesial temporal sclerosis after VEM hospitalization. In our study, while a figure 4 sign was observed in some seizures of the patients, it was observed that there was a versive head deviation in some seizures. This finding reveals that the more seizures we see in the VEM unit, the more accurate it will be to determine the epileptogenic focus. It may be more instructive to evaluate the patient not according to a single seizure but according to the semiological characteristics of all seizures observed in VEM and to perform lateralization accordingly. A study published in 2020 reported that patients in VEM had their first seizure on an average of the 5th day [10]. In another study, it was emphasized that patients with resistant epilepsy should stay in the VEM unit for at least 72 h [11]. However, these studies did not address the issue of how many seizures of patients should be recorded during VEM. We think that studies on this subject are also needed.
The M2e posture were defined as a tonic movement or lifting one arm in 1957 by Ajmone Marsan [12]. This posture starts with the flexion of the elbow and continues with the abduction and external rotation of the shoulder. The hand can be in a punch position or open. It is emphasized that the other arm should be free during this posture but should participate in the tonic activity that will develop later. Also, it was reported that versive head deviation might be seen before, simultaneously, or after this posture. The M2e posture occurs contralateral to the epileptogenic focus. In the study conducted by Ajmone Marsan and Marasly and colleagues in 2016, it is claimed that there is a strong lateralization significance indicating the contralateral hemisphere [8,9,10,11,12]. In another study conducted, it was reported that the figure 4 posture might occur following the M2e posture [1]. However, we did not evaluate the M2e posture in our study.
Studies conducted have shown that the asymmetric clonic jerk (last clonic jerk) has a specificity that lateralizes the epileptogenic region with the ipsilateral hemisphere at a rate of 83% [13, 14]. The last clonic jerk was also observed in our four patients in whom the figure 4 sign was observed, and both of them lateralized the same side for the epileptogenic focus. In a study examining the seizures of patients who remained seizure-free after focal surgical resection limited to the temporal, frontal, parietal, and occipital lobes, the positive predictive value of the lateralization finding of the last clonic jerk, which is ipsilateral, was found to be 86% [15].
Current studies show that lateralizing and localizing clinical semiological seizure features are of great significance in epileptogenic focus detection when evaluated together with ictal EEG and brain imaging methods. We think that the figure 4 sign is one of these critical clinical semiological features, and we think that more detailed investigations and studies with large populations are needed on this subject.
Our study has some limitations. These are the retrospective nature of the study, the small number of patients, the inclusion of patients whose epileptogenic focus is not identified, and the absence of invasive video-EEG.
