Drop attacks as defined above are usually without an identifiable mechanism, requiring no treatment if cardiologic studies are normal. On uncertain grounds, they are often attributed to brainstem ischemia. In only about one-quarter of such cases, according to Meissner and coworkers, can an association be made with cardiovascular or cerebrovascular disease to which treatment should be directed.
Orthopedic surgeons and rheumatologists are familiar with knee-buckling attacks, which they attribute to arthritic or tendinous disorders of the knee. Painful impulses arising in and around the knee could result in brief reflex silence of the antigravity muscles (primarily the quadriceps), producing a phenomenon akin to asterixis. Greenwood and Hopkins long ago proposed this mechanism. Although brief periods of silence have been recorded in the quadriceps muscles of patients with drop attacks, the reflex mechanism and its relationship to knee pain is speculative.
In epilepsy, whether convulsive or not, the arrest in consciousness is almost instantaneous and, as revealed by the EEG, is accompanied by a paroxysm of electrical activity occurring simultaneously in all of the cerebral cortex and thalamus. There are a number of important clinical distinctions between epileptic and syncopal attacks. The epileptic attack may occur day or night, regardless of the position of the patient; syncope rarely appears when the patient is recumbent, the only common exception being the Stokes-Adams attack. The patient’s color usually does not change at the onset of an epileptic attack; pallor is an early and almost invariable finding in most types of syncope except those caused by chronic orthostatic hypotension or hysteria, and it precedes unconsciousness. If an aura is present, it rarely lasts longer than a few seconds before consciousness is abolished. The onset of syncope is usually more gradual, and the prodromal symptoms are quite distinctive and different from those of seizures. In general, injury from falling is more frequent in epilepsy than in syncope, because protective reflexes are instantaneously abolished in the former. (Nevertheless, cardiogenic syncope is an important cause of hurtful falls, especially in the elderly.) The return of consciousness is slow in epilepsy, prompt in syncope; mental confusion, headache, and drowsiness are common sequelae of seizures, and physical weakness with clear sensorium, of syncope (a brief period of grogginess may follow vasodepressor syncope). Biting of the tongue is well known, albeit not always present in convulsion; it is exceptional in syncope. Repeated spells of unconsciousness in a young person at a rate of several per day or month are much more suggestive of epilepsy than of syncope.
Tonic spasm of muscles with upturning of the eyes is a prominent and often initial feature of epilepsy, but also occurs in the course of a faint and cannot be depended upon to make the distinction between the two processes. Urinary incontinence is a frequent occurrence in epilepsy, but it need not occur during an epileptic attack and may occasionally occur with syncope, so that it also cannot be used as a means of separating the disorders.
The EEG may be helpful in differentiating syncope from epilepsy. In the interval between epileptic seizures, the EEG, particularly if repeated once or twice, shows some degree of abnormality in 50 to 75 percent of cases, whereas it should be normal between syncopal attacks. Sometimes one must resort to continuous EEG monitoring to clarify the situation (this can be combined with continuous ECG recording). Another useful laboratory marker of a seizure, especially if unwitnessed, is an elevation of the serum creatine kinase (CK) concentration; such a finding occurs only infrequently in the rare case of syncope associated with extensive muscle trauma. Elevated prolactin levels have not proved discriminating enough for routine use in separating seizure from syncope but remain useful in distinguishing both of these from other causes of loss of consciousness, particularly hysteria, in which such elevations do not occur.