Neurological A spects of Syncope a nd Orthostatic I ntolerance

A sudden, unexpected loss of consciousness is one of the more dramatic and anxietyprovoking symptoms encountered by patients. Syncope, however, is a common manifestation of numerous disorders of varied mechanisms. The final common pathway in most, however, is insufficient cerebral perfusion to maintain consciousness. Symptoms short of frank syncope (presyncope) are also common and may appear relatively non-specific in isolation or out of context. A current view is to consider one’s capacity for postural and similar challenges as orthostatic tolerance that can be impaired by a wide variety of disorders and may become symptomatic under certain conditions. For diagnosis syncope must be differentiated from other processes with paroxysmal onset and altered consciousness such as seizures, drop attacks, metabolic disturbances, or psychiatric events. After many events, no residual abnormalities are evident on examination or on initial studies to prove a specific diagnosis. More than most areas of medicine, this lack of objective residua makes a detailed and accurate history the most important aspect of diagnosis. The distinction is vital for clinical decision-making and effective treatment. Once a designation is made, alternative diagnoses may be inadequately considered at later assessments, even if correct. This review focuses on syncope from the perspective of the neurologist and the disorders generally considered in the setting of acute, transient loss of consciousness. The numerous and important causes of syncope related to primary cardiac and pulmonary dysfunction (cardiac syncope) mostly due to insufficient cardiac output despite adequate venous supply including valvular disease, sustained arrhythmias, myocardial disease and heart failure, and structural heart and lung disease are not discussed. Many of these cardiac etiologies are clearly evident with pertinent signs on examination, other historical details, prior history, or abnormalities with initial