Utility of Video-EEG for Diagnosing and Understanding Transient Loss of Consciousness

Abstract

Diagnosing the cause of transient loss of consciousness (TLOC) is challenging due to overlapping symptoms and signs among various causes, as well as recall bias and the lack of reliable diagnostic algorithms covering all possible presentations and clinical settings. With the widespread use of smartphones and availability of video recordings in laboratory settings, semiological details become an increasingly important feature to differentiate between the different causes of TLOC; the latter is the focus of this chapter. We will first discuss the classical signs of cerebral hypoperfusion that may be seen in all forms of syncope. Depending on the rate and depth of this hypoperfusion a range of signs and symptoms could occur, e.g. dizziness or light-headedness, visual disturbances, unclear thinking, and eventually loss of consciousness. Electroencephalography (EEG) offers an important tool to review the depth of hypoperfusion. Two EEG patterns can be seen in syncope: the slow pattern and the slow-flat-slow pattern. Snoring, gasping, roving eye movements, upward deviation of the eyes, making sounds, and posturing are strongly associated with EEG flattening. Apart from the signs caused by the hypoperfusion, syncope may be accompanied by features that point towards the underlying cause. These include signs of autonomic activation (e.g. nausea and perspiration) in reflex syncope; profound and prolonged hypotension without TLOC in orthostatic hypotension causing ‘coat hanger pain’ or an ‘inability to act’ and palpitations and symptoms of heart failure in some forms of cardiac syncope. Syncope has many overlapping symptoms and signs with tonic-clonic seizures and psychogenic TLOC. Herein we provide a detailed discussion of the prodromal, ictal, and postictal signs and highlight the clinical contrasts.