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The most important diagnostic problem in epileptology is to distinguish epileptic seizures from syncope and from psychogenic attacks. A less common problem is the need to distinguish epilepsy from other paroxysmal disorders with which it may overlap. Improved understanding of ion channel disorders has blurred the definition of epilepsy.1
The diagnosis of episodic altered consciousness rests largely with the clinical history, notwithstanding the remarkable advances in the technology of imaging and neurophysiology. Common reasons for misdiagnosis are:
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- inadequate or missing history—for example, no witness
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- clonic movements or incontinence accompanying syncope or psychogenic attacks
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- undeserved emphasis on a family history of epilepsy or a history of febrile convulsions
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- overinterpretation of minor electroencephalography (EEG) abnormalities or normal age specific variants.
SYNCOPE
Syncope is the most common “non-epileptic” cause of altered consciousness. The two main types are reflex (vasovagal) and orthostatic syncope. Less common but more serious causes include cardiac and central nervous system syncope.
Reflex (vasovagal) syncope
This is caused by exaggerated but normal cardiovascular reflexes, and so occurs in otherwise healthy individuals, mainly children and young adults.
Clinical features
Table 1 shows characteristics distinguishing vasovagal syncope from epileptic seizures.
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Clinical distinction of reflex (vasovagal) syncope from seizures
Triggers include prolonged standing (school assembly), rising from lying (bathroom at night), hot crowded environments (restaurant), emotional trauma, and pain (doctor's surgery). Prodromal symptoms (presyncope) developing over 1–5 minutes include light headedness, nausea, sweating, palpitation, greying or blacking of vision, muffled hearing, and feeling distant.
A witness may describe pallor, sweating, and cold skin. Muscle tone is flaccid sometimes with a few uncoordinated clonic jerks occurring after the fall. A common error is to label syncope as a seizure, given a witness account of shaking (convulsive syncope).2 Incontinence and injury are uncommon and lateral tongue biting rare. Recovery is usually rapid and without confusion.
Mechanism
The mechanism is complex. Venous return falls when blood pools in either the legs (prolonged standing) or the splanchnic vessels (increased vagal tone—for example, response to seeing blood). Cardiac output therefore falls, but the blood pressure is maintained initially by sympathetically induced peripheral vasoconstriction. The …