Section 7:
Diseases of the Nervous System

7.1 Syncope

7.2 Seizures

7.3 Sleep Disorders

7.3.a. Narcolepsy
7.3.b. Sleep Apnea

A summary of the current fitness-to-drive guidelines(Diseases of the Nervous System) for medical practitioners from Australia (1998) and Canada (2000) is presented in Table 21.

7.1 Syncope

See discussion and review of syncope in Section 4 (Cardiovascular Disease).

7.2 Seizures

A seizure is a paroxysmal uncontrolled abnormal discharge of electrical activity in the gray matter of the brain, causing clinical signs and symptoms that interfere with normal functioning. A seizure is not a disease but is a symptom of underlying pathology. Numerous conditions can induce a seizure (e.g., central nervous system infections, hyperpyrexia, intracranial tumors, cerebral hypoxia, cerebral trauma, alcohol or drug withdrawal, etc.).

According to McLachlan (1993), up to nine percent of the population will have at least one seizure during their lifetimes. Estimated risks of a recurrence following a single unprovoked seizure range from 23 percent (Pearce and MacKinstosh, 1979) to 71 percent (Elwes, Chesterman, and Reynolds, 1985). Recently, Berg and Shinnar (1991) explored the reasons for the variability in estimated risk reported in the literature. Results of their meta-analysis revealed that three methodological factors explained much of the variance: 1) study inclusion criteria, 2) retrospective versus prospective ascertainment of patients, and 3) the interval between the first seizure and the time at which the risk was assessed. The average recurrence risk across the studies included in the meta-analysis was 51 percent. Relevant to this review was the finding that the risk of seizure recurrence was highest in studies of children only (54 percent), compared to studies of adults only (43 percent). Predictors of seizure recurrence included seizure etiology and electroencephalogram (EEG) abnormalities. An abnormal neurological status was associated with a substantially increased recurrence risk compared to those with idiopathic seizures (e.g., without underlying brain pathology). EEG abnormalities were associated with a higher risk of seizure recurrence.

Notably, patients with idiopathic seizures and normal EEGs were found to have a low recurrence risk of about 24 percent at two years. Finally, partial seizures were, in general, associated with an increased risk of seizure recurrence. Results of Berg and Shinnar's meta-analysis may be useful when making decisions about licensing decisions for individuals with first unprovoked seizures. Specifically, results from this meta-analysis suggest that two commonly assessed patient characteristics (seizure etiology and EEG results) are helpful predictors for seizure recurrence.

Epilepsy

Epilepsy, a common neurological disorder, is characterized by recurrent seizures that can involve loss of consciousness, convulsive movements or other motor activity, sensory phenomena, or behavioral abnormalities. Epilepsy has a prevalence rate of 0.7 percent (McLachlan, 1993) and an overall incidence of about 50 per 100,000 (Hauser, Annegers, and Rocca, 1996). The incidence of new-onset epilepsy is such that onset is highest in the first year of life, decreasing to a minimum during middle age (30s and 40s), and increasing again in individuals 60 years of age and older (Hauser, 1992).

Epileptic seizures often are classified into two broad groups, depending on etiology: 1) symptomatic or secondary epilepsy, and 2) idiopathic or primary epilepsy. In symptomatic or secondary epilepsy, the probable cause of the seizures often can be determined, whereas in idiopathic or primary epilepsy, specific causes cannot be found. Approximately two-thirds of epilepsy in young adults is idiopathic in origin. However, more than 50 percent of epilepsy in elderly individuals has a known cause (Hauser, Anderson, Lowenson, and McRoberts, 1992), including cerebrovascular disorders (~33 percent), brain tumors (~10-15 percent), and infections, trauma, or other secondary lesions (~23 percent) (Luhdorf, Jensen,and Plesne, 1986).

Classification of Epileptic Seizures

There are numerous classifications of epileptic seizures. The most widely accepted is the classification system advanced by the Commission on Classification and Terminology of the International League Against Epilepsy (1981). As can be seen from Table 15, within this system, seizures are classified as partial or generalized. The three most common types of seizures in adults are a) generalized tonic-clonic seizures (GTCSs), with convulsions (grand mal seizures), b) complex partial seizures (CPSs), with alterations of consciousness, and c) simple partialseizures (SPSs). Approximately one-third of all epileptic individuals have CPSs, with the prevalence increasing to approximately one-half in elderly epileptic individuals (Hauser, 1992).

Table 15  Classification System of Epileptic Seizures as Advanced by the Commission on Classification and Terminology of the International League Against Epilepsy (1981)

Source: from Commission on Classification and Terminology of the International League Against Epilepsy (1981). Available online at: http://neuroland.com/