S100B protein is a biomarker produced mainly by astrocytes and released into the bloodstream in the event of brain injury, with levels rising rapidly and markedly in acute conditions such as traumatic brain injury, stroke, or epileptic seizures, before declining quickly. Increased S100B levels following a convulsive seizure have been reported, suggesting potential value in distinguishing epilepsy from other causes; however, its use in the etiological assessment of transient loss of consciousness has not yet been studied. Loss of consciousness represents a common reason for Emergency Department visits and involves a wide range of causes, making diagnosis challenging due to often limited clinical history and resulting in numerous investigations. A biomarker such as S100B could help guide diagnosis more rapidly, particularly in distinguishing epilepsy from other causes, thereby reducing the need for additional tests and shortening hospital stay. To date, no study has evaluated the performance of S100B measurement in the etiological workup of transient loss of consciousness. The hypothesis underlying this study is that measurement of S100B levels in the Emergency Department could help differentiate epileptic seizures from other etiologies, particularly cardiac causes, and thus reduce additional investigations and hospital stay. This prospective observational study primarily aims to assess the diagnostic performance of S100B measurement for identifying epilepsy compared with other causes of transient loss of consciousness in adult patients presenting to the Emergency Department for this reason. The study will begin on April 30 and will last 15 months. In practice, eligible patients who do not oppose participation will undergo an additional blood sample at the time of initial sampling required for clinical management, with this sample used to measure plasma S100B levels; patient management will otherwise remain identical to standard care. Three months after the Emergency Department visit, an adjudication committee composed of a neurologist, a cardiologist, and an emergency physician will determine the final diagnosis based on all available data, including any additional investigations performed after the initial visit. The primary endpoint is the area under the ROC curve (AUROC) of S100B measurement, evaluating its ability to discriminate epilepsy from other causes of transient loss of consciousness.

Inclusion Criteria:

• • Adult ≥ 18 years old

  • Presentation to the Emergency Department of Henri Mondor University Hospital
  • History of loss of consciousness
  • Undergoing a blood test as part of Emergency Department care
  • Covered by social security
  • Has agreed to participate in the study

Exclusion Criteria:

• Symptoms occurring more than 12 hours ago

  • History of head trauma without brain imaging performed
  • History of head trauma with intracranial bleeding confirmed on brain imaging
  • Refusal to participate in the study
  • Pregnant and/or breastfeeding women
  • Individuals unable to provide consent, particularly due to cognitive impairment
  • Individuals under legal protection:
  • Placed under guardianship
  • Deprived of liberty (incarcerated or hospitalized without consent)

The study population will consist of adult patients presenting to the Emergency Department of Henri Mondor University Hospital during the inclusion period for an episode of transient loss of consciousness. Eligible patients will be screened consecutively and included if they meet all predefined inclusion criteria and none of the exclusion criteria.

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