Finally, after careful evaluation of patients with syncope and the exclusion of the many forms of the condition described earlier, there remains a significant proportion (one-third to one-half, according to Kapoor and 40 percent in the earlier-noted Framingham Heart Study) in which a cause for the syncope cannot be ascertained. The question of whether a single positive tilt-table test signifies that a prior episode of syncope was neurocardiogenic is not resolved; this obviously has a bearing on the proportion of cases that remain without a diagnosis. If the episodes are repetitive and erratically spaced, a cardiac arrhythmia, intraventricular conduction defect, or seizure should be sought by use of prolonged cardiac rhythm monitoring and conduction studies as well as long-term EEG recordings.
Anxiety Attacks and the Hyperventilation Syndrome
These are probably the most important diagnostic considerations in unexplained faintness without syncope. The light-headedness of anxiety and hyperventilation are frequently described as a feeling of faintness, but a loss of consciousness does not follow (see Linzer et al, 1990). Such symptoms are not accompanied by facial pallor or relieved by recumbency. The diagnosis is made on the basis of the associated symptoms, the absence of laboratory and tilt-table abnormalities, and the finding that part of the attack can be reproduced by having the patient hyperventilate. The symptoms produced in this way mimic the persistent or episodic dizziness that accompanies anxiety and panic states (see Chap. 14). When anxiety attacks are combined with a Valsalva effect or prolonged standing, fainting may occur. The relationship of anxiety-panic to the previously described postural orthostatic tachycardia syndrome is uncertain.
In diabetics and some nondiabetics, hypoglycemia may be an obscure cause of episodic weakness and very rarely of syncope. With progressive lowering of blood glucose, the clinical picture is one of hunger, trembling, flushed facies, sweating, confusion, and, finally, after many minutes, seizures and coma. The diagnosis depends largely on the history, the documentation of reduced blood glucose during an attack, and reproduction of the patient’s spontaneous attacks by an injection of insulin or hypoglycemia-inducing drugs (or ingestion of a high-carbohydrate meal in the case of reactive hypoglycemia). Fasting hypoglycemia suggests the presence of an insulin-secreting tumor (insulinoma).
Acute hemorrhage, usually within the gastrointestinal tract, is a cause of weakness, faintness, or even unconsciousness when the patient stands suddenly. The cause (gastric or duodenal ulcer is the most common) may remain inevident until the passage of black stools.
This term has been applied to falling spells that occur without warning and without loss of consciousness or postictal symptoms. The patient, usually elderly, suddenly falls down while walking or standing, rarely while stooping. The knees inexplicably buckle. There is no dizziness or impairment of consciousness, and the fall is usually forward, with scuffing of the knees and sometimes the nose. The patient, unless obese, is able to right himself and to rise immediately and go his way, quite embarrassed. There may be several attacks during a period of a few weeks and none thereafter. The interval EEGs and ECGs are normal. One potential mechanism is a lapse of tone in leg muscles during the silent phase of an unnoticed myoclonic or axterixis jerk. Primary orthostatic tremor (see Chap. 4) has a similar appearance. Drop attacks also occur in acute hydrocephalus, and with the Chiari malformation, and these patients, although conscious, may not be able to arise for several hours. Rare instances of Ménière disease, in which the patient is suddenly thrown to the ground (“otolithic catastrophe of Tumarkin,” see “Ménière Disease and Other Forms of Labyrinthine Vertigo” in Chap. 14) may be mistaken for a syncopal or drop attack, but only briefly, until vertigo becomes prominent.