Transient loss of consciousness with muscle jerks during a flight: syncope or epilepsy?

The differential diagnosis of a patient with a transient loss of consciousness accompanied by muscle jerks includes an epileptic seizure and an episode of convulsive syncope. In the present case the short duration of unconsciousness and rapid reorientation after regaining consciousness makes an epileptic seizure highly unlikely. An underlying cardiac abnormality is also unlikely, since the patient has no cardiac history and both the physical exam and the EKG were normal. Thus, the current case report points in the direction of convulsive vasovagal syncope. Vasovagal episodes are the most common in-flight medical events [1]. In addition to prolonged motionless sitting, mild hypoxia occurring during air travel (the cabin pressure on commercial aircraft is usually adjusted to be equivalent to the barometric pressure found at an altitude of 1500 to 2500 m above sea level) may be involved. Even mild hypoxia predisposes to vasovagal faints. It appears that hypoxic syncope results from the superimposed vasodilator effects of hypoxia on the cardiovascular system [2].

Jerky movements mimicking an epileptic seizure may occur during syncope. The circumstances determining whether they do or do not appear are not well known. In clinical practice there is a clear tendency for jerks to appear following prolonged asystole of at least 10-14 seconds or a prolonged period of very low blood pressure. In the fainting lark, an experimentally induced syncope with a very abrupt cessation of cerebral perfusion (see case 4 in this section) the jerky movements appeared almost as soon as the subject hit the ground. The ‘anoxic threshold’ for myoclonic jerks is lower in children than in adults, and it is lowest in early childhood [3][4]. In contrast to clonic movements in epilepsy, jerks in syncope are usually not rhythmic, not synchronous in the extremities, and less coarse as compared to those observed in epilepsy. Furthermore, in syncope the jerky movements never occur before falling, whereas in epilepsy they may occur before falling [5][6]. In a typical tonic-clonic epileptic seizure, however, the fall is due to the stiff tonic phase and the clonic movements occur afterwards. The myoclonic activity is presumably due to a lack of inhibition from higher centers, but the site of origin remains unknown[5].

The prevalence of myoclonic jerks in patients with syncope is not well known. In a prospective study Newman et al. documented tetany, clonic movements, and twitching in 46% of 178 blood donors having a vasovagal reaction[7]. In the fainting lark myoclonic jerks occurred in 90%. These vastly differing percentages suggest that the occurrence of jerky movements depends on how hypoperfusion.affects cerebral perfusion, but which factors are involved is unknown. Urinary incontinence is uncommon in reflex syncope, but does occur and so does fecal incontinence. Incontinence cannot be used as discriminating factors between epilepsy and syncope[8][9]. Typical symptoms and signs of epilepsy are tongue-biting, a cyanotic facial color and an aura. Benbadis et al. compared 34 patients with epileptic seizures to 45 syncopal patients. Eight patients with documented epileptic seizures suffered a lateral tongue bite. The tongue was lacerated in only one of 45 patients with syncope and this was at the tip, suggesting that lateral tongue biting is highly specific (99%) for the diagnosis of epileptic seizures[10]. Consistent turning of the head to one side is also reported as a specific sign for epilepsy[9], but lateral deviation of the head was also observed in experimental syncope induced by ocular compression[11]. Emotional stress has been reported as a precipitating factor both for reflex syncope and epilepsy [12][13], but in syncope emotional factors may provoke and thus occur immediately prior to fainting, whereas stress in epilepsy appears to have a less immediate effect in the sense that seizures may occur during a longer period of stress. Important symptoms that distinguish between reflex syncope and epilepsy are the duration of the loss of consciousness and postictal confusion. In the recovery phase of an episode of syncope there is usually little to no confusion[8][9]. Finally, circumstances such as prolonged standing and autonomic symptoms such as cold sweat and nausea make epilepsy unlikely as the cause for the event [7]. Epileptic seizures usually do not have a clear trigger. They occur more randomly i.e. in standing, sitting or supine position.

Sensitivity and specificity of data from the medical history are compared in Table 1 and Table 2.