Patient and Study Identification
The patient is a 10-year-old boy sent by the referring specialist neurologist, whom the patient visited after his mother had found him experiencing seizure twice during the past month. The patient was first diagnosed with absence epilepsy when he was 5 years of age, and has not experienced seizures since he was 8 years of age. The purpose of this electroencephalography (EEG) study is to identify the type of epilepsy in this case so that the patient can receive the correct treatment.
History
The patient had a normal birth and experienced healthy development until the age of 5, when his childhood absence epilepsy was first diagnosed. The episodes stopped at the age of 8, but two recent seizures occurred now that the patient is 10 years of age. The patient’s mother found the boy during both episodes. The mother reported hearing guttural sounds in the bedroom and found that the tonic-clonic activity lasted approximately 30 seconds in both cases. Both seizures occurred in the morning upon waking, and they were followed by a period of disorientation and slurred speech before recovery.
The patient is not taking medication and is reported to be a good student, who also participates in sports. The physical examination included a general and detailed neurological examination. No abnormalities were reported after the physical examination.
According to the family history, the patient’s mother experienced febrile seizures while she was a toddler. However, a diagnosis of epilepsy or other neurological disorders in the family was not reported.
Procedure
Two EEG recordings with different parameters were conducted. The recording A (Figure 1) was started at 15:19:05 and the parameters were sens: 10 µV/mm, HF: 60 Hz, and TC: 0.10 seconds. The recording B (Figure 2) was started at 11:09:49 with the parameters sens: 15 µV/mm, HF: 70 Hz, and TC: 0.10 seconds.
The standard International 10-20 system was used for electrode placement for both recordings (American Electroencephalographic Society, 1991). Electrocardiography (EKG) was also performed during EEG and provided along with the EEG recording, which is important because it provides information about the relationship between the brain and the heart (Tatum, 2008).
Technical Description
Two normal features of the EEG recording A, which is shown in Figure 1, have been observed. First, the waves in recording A are alpha frequencies (8-13 Hz), both before and after the abnormalities were detected in the middle of the recordings. The patient was in a waking state during the EEG study, but alpha frequencies are expected to appear when the patient’s eyes are closed. Second, the EKG shows a consistent rhythm, which is usually the case in most EEG recordings obtained from epileptic patients. EKG abnormalities can appear during myoclonic seizures (Kaplan & Tatum, 2008), which the current patient is experiencing, but they are not always correlated with seizures.
Two abnormal features were observed in recording A. First, even though alpha frequencies are observed in most points, higher frequencies were observed in frontal polar, frontal lobe, and temporal lobe sites. Those frequencies were present throughout the entire duration of the recording before and after the generalized epileptiform discharge. Because the frequency is continuous throughout the recording, those frequencies are expected to be muscle artifacts because the EEG is susceptible to interferences caused by the activation of the head muscles in those regions.
Second, in the middle of the recording, it is possible to notice a generalized epileptiform discharge, which is correlated with idiopathic generalized epilepsies (Tatum & Benbadis, 2008). The duration of the burst was less than 2 seconds, which is common in cases that involve absence seizures. Although absence seizures usually result in symmetric spike-and-wave discharges, the burst observed in recording A is disorganized, which makes it an atypical absence seizure (Kaplan, & Tatum, 2008).
Figure 1. EEG recording A showing a generalized epileptiform discharge, approximately 2 seconds in duration.
Figure 2. EEG recording B showing generalized, disorganized spike-and-wave activity, occipital spike and wave discharges, and muscle activation in the frontal, frontal polar, and temporal locations.
One normal feature was observed in the EEG recording B, which is shown in Figure 2. The EKG demonstrated that changes in EEG spikes are not associated with the heart, which continues to work at a consistent rate.
Three abnormal features were observed in recording B. First, the interictal EEG was normal at onset, but quickly became disorganized and asymmetric. The duration of the generalized epileptiform discharge was approximately 4 seconds. Although the frequency and amplitude in the EEG slightly normalized after the generalized epileptiform discharge, several intermittent discharges can be observed on multiple locations.
Second, the spikes and waves at O1 and O2 (i.e., P3-O1, P4-02, T5-O1, T6-O2) were observed at the first second of the recording. At O1, it is possible to observe the spike-and-wave discharge, whereas the O2 locations show multipeak waves. Discharges on a smaller scale were also observed a second later in the same locations, but they were also associated with a generalized frequency increase in all other locations.
The third and final abnormality observed in recording B is the increased frequency at the beginning of the recording on points Fp1-F3, Fp2-F4, Fp1-F7, Fp2-F8, F8-T4, and T4-T6. However, the amplitude remained consistent even after the activities observed subsided. Although this abnormality could be considered as an interference of the muscular activation in the aforementioned regions, it is important to note that the activation of head muscles is characteristic for absence seizures, so that observation is considered an abnormality related to the patient’s condition.
EEG Diagnosis
A total of three abnormalities were observed during this EEG study. First, the generalized epileptiform discharges were observed in both recordings. Those abnormalities have been associated with idiopathic generalized epilepsy (Tatum & Benbadis, 2008). Therefore, the diagnosis in this case can be found in that group of idiopathic generalized epilepsies. The interictal EEG was normal at onset became disorganized and asymmetric in both recordings during the spike-and-wave discharge patterns, so the most likely diagnosis is expected to be myoclonic-astatic epilepsy. However, a differential diagnosis must be performed because of the other abnormalities observed during this study.
The spike and wave discharges were observed at O1 and O2 in recording B, and that observation is consistent with the EEG recordings in cases of benign occipital lobe seizures (Chary & Rajendran, 2013). Benign occipital lobe seizures are not always localized and could also be associated with generalized epileptiform discharges, so it is not possible to exclude the possibility of occipital seizure syndromes in this case.
Increased muscle activity was observed in both recordings. However, in recording A, the muscle artifact is considered a possible interference because the frequency is consistent throughout the recording. In recording B, the increased muscles activity is expected because the patient cannot control the jerking movements during absence seizures, especially in the head, neck, and shoulder muscles (Shorvon, Andermann, & Guerrini, 2011). Although it is possible that even single motor unit activity in the head and neck region can interfere with EEG recordings (Yilmaz, Ungan, Sebik, Uginčius, & Türker, 2014), the patient’s diagnosis of absence epilepsy suggests that involuntary movements of the head, neck, and shoulder muscles are to be expected.
Clinical Interpretation
The spikes appearing in the patient’s EEG recordings are consistent with epileptic conditions that are associated with cortex stimulation, which leads to the appearance of high-voltage waves (Teplan, 2002). Based on the previous diagnosis of absence epilepsy and the patient’s medical history, it is possible to confirm that the patient has childhood absence epilepsy, but it is important to further specify the type of epilepsy so that the patient can receive appropriate treatments.
In order to verify the diagnosis, electromyography (EMG) is recommended to determine if the abnormalities detected in the EEG recordings are also associated with rhythmic myoclonic jerks of the deltoid and neck muscles (Shorvon et al., 2011). The diagnosis is consistent with the early childhood onset of the disease. The mean age of epilepsy with myoclonic absences is 7 years, and the patient should experience daily myoclonic absences that usually occur upon awakening or because of hyperventilation (Bureau & Tassinari, 2005). Because the patient’s episodes occurred in the morning and lasted less than 60 seconds, the description provided by his mother is consistent with the symptoms of epilepsy with myoclonic absences.
Although absence epilepsy was diagnosed when the patient was 5 years of age, it is important to note that the specific condition in this case is most likely myoclonic-astatic epilepsy. Although myoclonic-astatic epilepsy accounts for only 2% of all childhood epilepsies, the onset usually occurs between 2 and 6 years of age, and the remission may occur after a few months or years without affecting the cognitive functions of the patient (Guerrini, 2006). Those characteristics of myoclonic-astatic epilepsy are consistent with the patient’s history, which shows that no episodes have been reported for the past 2 years. Furthermore, the patient is also reported to be a good student and active in sports, so it is possible to suggest that the boy is one of those that did not experience cognitive impairments associated with myoclonic-astatic epilepsy.
Another reason to suspect myoclonic-astatic epilepsy is the fact that different EEG abnormalities are associated with each type of epilepsy. Epilepsy with myoclonic absences usually shows 3 Hz generalized spike-and-wave patterns during episodes, and those patterns are regular and symmetrical (Shorvon et al., 2011). However, this case shows disorganized interictal spikes and waves, which are characteristic in cases of myoclonic-astatic epilepsy (Shorvon et al., 2011). The physical examination found that the patient is asymptomatic, which is consistent with the fact that myoclonic-astatic epilepsy is usually not associated with symptoms other than seizures.
According to the family history, the patient’s mother had febrile seizures when she was a toddler. Even though febrile seizures increase the risk for developing epilepsy, the mother’s medical history does not include an epilepsy diagnosis. Therefore, it is expected that heredity did not play a role in the onset and development of epilepsy in this case. The heredity risk of developing idiopathic generalized epilepsies is estimated between 4% and 10%, and the EKG in epilepsies with presumed complex inheritance typically involves changes in heart rate and may show periods of sudden cardiac arrest (Shorvon et al., 2011). No changes in the EKG recordings were observed during the patient’s seizures, so it is possible to rule out complex inheritance as a potential explanation of the patient’s condition.
Finally, it is important to address the occipital spikes observed in recording B before the seizure was recorded. Occipital spikes are usually associated with childhood-onset benign occipital lobe seizures and are considered epileptiform abnormalities if intermixed spikes are present (Benbadis, 2008; Chary & Rajendran, 2013; Tatum & Benbadis, 2008), which was the case with this patient’s EEG recording.
Previous studies claimed that seizures in those cases comprise of various disturbances (e.g., vomiting or eye deviation) and can last from 3 minutes up to several hours (Panayiotopoulos, 2000). However, several factors can interfere with the clinical features of occipital seizures and contribute to the shifting of seizure locations rather than localizing it in the occipital regions (Ohtsu et al., 2003). The common behavioral and autonomic disturbances associated with occipital seizures may be completely absent while the seizures could last no more than one minute in specific occipital epilepsies (Taylor et al., 2003). Children with early-onset benign occipital seizures were also grouped based on localization, and two of the five groups identified were those with persistent occipital focus and those with a generalized EEG pattern (Ohtsu et al., 2003).
Current evidence suggests that idiopathic occipital epilepsies can show both occipital epileptiform activity and generalized spike-and-wave discharges (Gastaut, 1982; Panayiotopoulos & Aicardi, 1989; Yalcin, Kaymaz, & Forta, 1997). Therefore, the EEG studies alone will not be sufficient to perform a differential diagnosis.
Benign occipital seizures are usually not associated with neurostructural changes (Chary & Rajendran, 2013). However, magnetic resonance imaging (MRI) is recommended to further investigate the type of epilepsy the patient is experiencing. Specifically, malformations in cortical development associated with occipital epilepsies were found to be focal cortical dysplasia, periventricular heterotopias, subcortical band heterotopias, and polymicrogyria (Taylor, Scheffer, & Berkovic, 2003). Without MRI, it will not be possible to perform a reliable differential diagnosis as occipital epilepsies often resemble other seizures and may not show up on scalp EEG to suggest further localized investigations.
Based on the current EEG recordings and medical history information available from the patient, the most likely diagnosis in this case is myoclonic-astatic epilepsy. However, further tests are recommended to verify myoclonic-astatic epilepsy and eliminate the possibility of syndromes associated with occipital seizures. A follow-up interview with the patient and his mother is also warranted to determine the frequency of the seizures. Absence epilepsy is usually associated with daily seizures, so even though a spontaneous remission is not unusual in cases of myoclonic-astatic epilepsy, it is important to determine if the seizures occurred more frequently than the mother knows.
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