Under a Spell: Neurologic Evaluation of Presyncope as a Feature of Dysautonomia.

While syncope is characterized by a sudden and temporary loss of consciousness caused by decreased blood flow to the brain and is easily recognized by its clinical features, presyncope involves a sensation of impending fainting, often accompanied by autonomic symptoms. Presyncope is less characterized and studied than syncope, presenting a particular diagnostic challenge in neurology clinics. Neurologists commonly encounter patients with presyncope in outpatient settings or during consultation at the emergency department after cardiopulmonary causes have been excluded. Differential diagnosis of recurrent presyncope is broad but from a neurologic standpoint falls into multiple neurologic categories, including complex partial seizures, basilar or vestibular migraine, dysautonomia, cataplexy, alteration in cerebrospinal fluid flow, Meniere's disease, posterior circulation transient ischemic attacks and others. Here, we review presyncope as a feature of dysautonomia and common autonomic disorders, such as neurocardiogenic syncope, postural orthostatic tachycardia syndrome, orthostatic hypotension and orthostatic intolerance. We discuss clinical and neurologic exam findings, diagnostic tests, differential diagnosis and treatment of presyncope as a manifestation of common autonomic disorders.