Chapter 2 Episodic Impairment of Consciousness
In patients with episodic impairment of consciousness, diagnosis relies heavily on the clinical history described by the patient and observers. Laboratory investigations, however, may provide useful information. In a small number of patients, a cause for the loss of consciousness may not be established, and these patients may require longer periods of observation. Table 2.1 compares the clinical features of syncope and seizures.
Table 2.1 Comparison of Clinical Features of Syncope and Seizures
| Features | Syncope | Seizure |
|---|---|---|
| Relation to posture | Common | No |
| Time of day | Diurnal | Diurnal or nocturnal |
| Precipitating factors | Emotion, injury, pain, crowds, heat, exercise, fear, dehydration, coughing, micturition | Sleep loss, drug/alcohol withdrawal |
| Skin color | Pallor | Cyanosis or normal |
| Diaphoresis | Common | Rare |
| Aura or premonitory symptoms | Long | Brief |
| Convulsion | Rare | Common |
| Other abnormal movements | Minor twitching | Rhythmic jerks |
| Injury | Rare | Common (with convulsive seizures) |
| Urinary incontinence | Rare | Common |
| Tongue biting | No | Can occur with convulsive seizures |
| Postictal confusion | Rare | Common |
| Postictal headache | No | Common |
| Focal neurological signs | No | Occasional |
| Cardiovascular signs | Common (cardiac syncope) | No |
| Abnormal findings on EEG | Rare (generalized slowing may occur during the event) | Common |
EEG, Electroencephalogram.
Syncope
The pathophysiological basis of syncope is the gradual failure of cerebral perfusion, with a reduction in cerebral oxygen availability. Syncope refers to a symptom complex characterized by lightheadedness, generalized muscle weakness, giddiness, visual blurring, tinnitus, and gastrointestinal (GI) symptoms. The patient may appear pale and feel cold and “sweaty.” The onset of loss of consciousness generally is gradual but may be rapid if related to certain conditions such as a cardiac arrhythmia. The gradual onset may allow patients to protect themselves from falling and injury. Factors precipitating a simple faint are emotional stress, unpleasant visual stimuli, prolonged standing, or pain. Although the duration of unconsciousness is brief, it may range from seconds to minutes. During the faint, the patient may be motionless or display myoclonic jerks, but never tonic-clonic movements. Urinary incontinence is uncommon. The pulse is weak and often slow. Breathing may be shallow and the blood pressure barely obtainable. As the fainting episode corrects itself by the patient becoming horizontal, normal color returns, breathing becomes more regular, and the pulse and blood pressure return to normal. After the faint, the patient experiences some residual weakness, but unlike the postictal state, confusion, headaches, and drowsiness are uncommon. Nausea may be noted when the patient regains consciousness. The causes of syncope are classified by their pathophysiological mechanism (Box 2.1), but cerebral hypoperfusion is always the common final pathway. Wieling et al. (2009) reviewed the clinical features of the successive phases of syncope.
History and Physical Examination
The history and physical examination are the most important components of the initial evaluation of syncope. Significant age and sex differences exist in the frequency of the various types of syncope. Syncope occurring in children and young adults is most frequently due to hyperventilation or vasovagal (vasodepressor) attacks and less frequently due to congenital heart disease (Lewis and Dhala, 1999). Fainting associated with benign tachycardias without underlying organic heart disease also may occur in children. Syncope due to basilar migraine is more common in young females. When repeated syncope begins in later life, organic disease of the cerebral circulation or cardiovascular system usually is responsible.
The neurologist should inquire about the frequency of attacks of loss of consciousness and the presence of cerebrovascular or cardiovascular symptoms between episodes. Question the patient whether all episodes are similar, because some patients experience more than one type of attack. In the elderly, syncope may cause unexplained falls lacking prodromal symptoms. With an accurate description of the attacks and familiarity with clinical features of various types of syncope, the physician should correctly diagnose most patients (Brignole et al., 2006; Shen et al., 2004). Seizure types that must be distinguished from syncope include orbitofrontal complex partial seizures, which can be associated with autonomic changes, and complex partial seizures that are associated with sudden falls and altered awareness, followed by confusion and gradual recovery (temporal lobe syncope). Features that distinguish syncope from seizures and other alterations of consciousness are discussed later in the chapter.
During syncope due to a cardiac arrhythmia, a heart rate faster than 140 beats per minute usually indicates an ectopic cardiac rhythm, whereas a bradycardia with heart rate of less than 40 beats per minute suggests complete atrioventricular (AV) block. Carotid sinus massage sometimes terminates a supraventricular tachycardia, but this maneuver is not advisable because of the risk of cerebral embolism from atheroma in the carotid artery wall. In contrast, a ventricular tachycardia shows no response to carotid sinus massage. Stokes-Adams attacks may be of longer duration and may be associated with audible atrial contraction and a first heart sound of variable intensity. Heart disease as a cause of syncope is more common in the elderly patient (Brady and Shen, 1999). The patient should undergo cardiac auscultation for the presence of cardiac murmurs and abnormalities of the heart sounds. Possible murmurs include aortic stenosis, subaortic stenosis, or mitral valve origin. An intermittent posture-related murmur may be associated with an atrial myxoma. A systolic click in a young person suggests mitral valve prolapse. A pericardial rub suggests pericarditis.
Causes of Syncope
Paroxysmal Tachycardia
Supraventricular tachycardias include atrial fibrillation with a rapid ventricular response, atrial flutter, and the Wolff-Parkinson-White syndrome. These arrhythmias may suddenly reduce cardiac output enough to cause syncope. Ventricular tachycardia or ventricular fibrillation may result in syncope if the heart rate is sufficiently fast and if the arrhythmia lasts longer than a few seconds. Patients generally are elderly and usually have evidence of underlying cardiac disease. Ventricular fibrillation may be part of the long QT syndrome, which has a cardiac-only phenotype or may be associated with congenital sensorineural deafness in children. In most patients with this syndrome, episodes begin in the first decade of life, but onset may be much later. Exercise may precipitate an episode of cardiac syncope. Long QT syndrome may be congenital or acquired and manifests in adults as epilepsy. Acquired causes include cardiac ischemia, mitral valve prolapse, myocarditis, and electrolyte disturbances (Ackerman, 1998) as well as many drugs (Goldschlager et al., 2002). In the short QT syndrome, signs and symptoms are highly variable, ranging from complete absence of clinical manifestations to recurrent syncope to sudden death. The age at onset often is young, and affected persons frequently are otherwise healthy. A family history of sudden death indicates a familial short QT syndrome inherited as an autosomal dominant mutation. The ECG demonstrates a short QT interval and a tall and peaked T wave, and electrophysiological studies may induce ventricular fibrillation (Gaita et al., 2003
