Electrical status epilepticus in sleep (ESES) is a pattern of abnormal discharges in the electroencephalogram (EEG). Children who have this pattern present seizures and neuropsychological regression. There are no studies that systematically evaluate the response of abnormal discharges in the EEG, seizures and neuropsychological regression to different antiepileptic treatments. Therefore, treatment strategies in ESES are not based on scientific evidence. High-dose benzodiazepines such as diazepam (valium) have been reported to improve the severe EEG abnormalities of patients with ESES in the short-term. But the long-term response of seizures and neuropsychological regression has not been systematically studied. Clobazam is a benzodiazepine derivative with antiepileptic properties. The pharmacologic properties of clobazam make of this drug a particularly useful option in ESES: in patients with ESES the alpha-2 subunit of the GABA receptor is preferentially up-regulated and clobazam may have a higher affinity for this particular subunit, so investigators expect a higher effect of this drug on ESES patients than with other benzodiazepines (Loddenkemper et al, in preparation). The aim of our study is to objectively evaluate the response to clobazam treatment of neuropsychological deficits, seizures and abnormal discharges in the EEG in patients with ESES. Clobazam treatment is used in routine clinical practice and investigators will objectively quantify its effect.

Our working hypothesis is that high-dose clobazam treatment may control the abnormal epileptiform discharges in the EEG in patients with ESES. The reduction in abnormal epileptiform discharges may lead to an improvement in neuropsychological deficits and seizures. The predicted improvement in seizures and neuropsychological function would lead to a better quality of life in these patients.

- A. RESEARCH METHODS

Study design. Investigators will perform a prospective descriptive cohort study with historical controls.

Participating institutions. Children's Hospital Boston (PI: Tobias Loddenkemper) and Children's Hospital Colorado (PI: Kevin Chapman).

Patients. Investigators will enroll patients with ESES studied at our centers and treated with high-dose clobazam treatment as decided by the clinical epileptologist.

The diagnosis of ESES will be confirmed based on neuropsychological regression in at least one domain of development, the presence of seizures that appear in an age-related manner and the presence in the EEG of the ESES pattern (Loddenkemper, et al. 2011a).

Contact with the patients. Once that the potential candidate is recognized (patient with ESES, a change in medication regimen is decided that includes initiation of clobazam), the research team will contact the primary epileptologist. The primary epileptologist will contact the patient in order to check whether the family and/or patient would like to be contacted for this research protocol. If the patient agrees to be contacted, the research team will contact the patient in order to propose them to participate in the study.

EEG assessment. Investigators will assess the epileptiform activity in the long-term monitoring unit before and after treatment for every patient.Assessment of clinical data. The clinical charts of the patients included in the study will be collected reviewed for relevant clinical information. This information will be updated and complemented with the patient and/or the family during the admissions for long-term monitoring. Assessment of neuropsychological data: A battery of neuropsychological tests will be performed by board-certified clinical neuropsychologists to obtain information regarding cognitive abilities.

Safety measures. Investigators will continuously monitor patients for adverse effects during hospitalization and provide them with contact information for continuous report of possible adverse effects. Potential risk to subjects. As subjects will be using a FDA-approved drug for the treatment of epilepsy their risk will be the same as in routine clinical care. There will not be risks associated with the specific use of clobazam as it is routinely used for clinical care and the decision to use it or not will depend on the primary provider and not on the research team. Other potential risks are related with the loss of privacy and confidentiality. Investigators will develop mechanisms to ensure protection of patients' privacy and confidentiality.

Quality control method. Investigators will perform quality control measures every 5 collected patients at Children's Hospital Boston. Additionally, independent medical monitoring will be implemented.

- B. STATISTICAL ANALYSIS

Calculation of the sample size. Our previous study with diazepam treatment (Sánchez Fernández, et al. in press-a) found that the difference in epileptiform activity before and after treatment was of around 30%. There are no other data available on the quantification of the response of epileptiform activity to antiepileptic treatment.

- C. PLANS FOR MISSING DATA

Recruitment of patients. Patients with ESES frequently belong to the category of patients that are not able to understand the study protocol both because of their age and because of neuropsychological regression. Their families and/or caretakers will decide in most cases about study enrollment and the patient consent/assent will be looked for when developmentally possible. Although studies with patients with severe developmental delays pose significant challenges, the burden of participating in the study will not be significantly different from the burden of normal clinical care. Additionally this study will be performed at centers that are familiar with the care of patients with severe developmental delay.

Sample size. Power calculation for the proposed study is challenging due to the novel approach. Our preliminary data, however, strongly favor feasibility and completion.

Inclusion Criteria:

• A change in treatment regimen is required because of very active epileptiform activity during sleep and neuropsychological regression. This means that only patients with very active epileptiform activity and, therefore, with a need for a change in treatment regimen as clinically indicated will be potentially eligible. Additionally, a prior clinical decision to use clobazam should have been made by the primary epileptologist in order to participate in the study.
• Availability for clinical, neuropsychological and EEG follow-up.

Exclusion Criteria:

• Electro-clinical evolution that does not require a change in medication regimen or changes in medication regimen that do not include clobazam.

Investigators will enroll patients with ESES studied at our centers and treated with high-dose clobazam treatment as decided by the clinical epileptologist. Patients with ESES are monitored once or twice a year in the long-term electroencephalogram monitoring unit to assess epileptiform activity. Patients with very active discharges and neuropsychological regression require a change in their treatment regimen. If the treating epileptologist decides that high-dose cloblazam treatment is indicated for clinical reasons, then the patient will be offered to participate in the study. The research team will not be responsible for or influence the treatment decisions in any way.