Hauser and Kurland reported an increase in the incidence of seizures as the population ages—from 11.9 per 100,000 in the 40to 60-year-old age group to 82 per 100,000 in those 60 years of age or older. Often, these individuals live alone so there is no witness to the event, they have multiple medical problems, they may have cognitive difficulty that impedes an accurate history, multiple medications are almost the rule, and cerebral imaging is likely to show abnormalities that may not be referable to the problem at hand.
A person in this age group who begins to have seizures of either focal or generalized type may harbor a primary or secondary tumor, a past cerebral infarct, or a traumatic cortical scar that had not declared itself clinically. For example, according to Sung and Chu, previous infarcts are by far the most common lesions underlying status epilepticus in late adult life. Probably the nature of the population in a given clinic determines the relative frequency of underlying causes. In any case, cerebral imaging usually settles the issue.
However, many seizure-like events in this age group are the result of a cardiac arrhythmia, particularly ventricular tachycardia but also cardiac disorders not related to rhythm such as aortic stenosis. Therefore, ECG and long-term monitoring of heart rhythm are useful ancillary tests if the episode remains unexplained.
Cortical and subcortical lesions, the result of previous traumatic contusions, are a particularly important cause of seizures; the lesions are revealed by brain imaging and are typically located in the anterior frontal and temporal lobes. Brain abscess and other inflammatory and infectious illnesses remain common causes of adult seizures in tropical regions. In the elderly, seizures as a result of advanced Alzheimer and other degenerative diseases occur in up to 10 percent of cases; moreover, these patients are subject to falls, subdural hematoma, and all other illnesses of old age, such as cancer, that secondarily affect the brain. In individuals with cancer, cerebral metastasis is certainly a common cause of a first seizure.
In the common case of an adult with a first unexplained seizure, it has been our practice not to administer an antiepileptic medication unless there is an underlying structural lesion or an abnormality on a single EEG or with prolonged monitoring and to reevaluate the situation in 6 to 12 months. The decision regarding starting treatment in an older adult is informed by a number of factors including occupation, need for driving, safety of home environment, use of alcohol and other sedatives, anticipated compliance, and drug interactions. Usually, a second MRI and EEG are performed to exclude focal abnormalities that were not appreciated during the initial evaluation, but often these studies are again unrevealing. This approach has been prompted by data such as those of Hauser and colleagues, who found that about one-third of patients with a single unprovoked seizure will have another seizure within 5 years; the risk is even greater if there is a history of seizures in a sibling, a complex febrile convulsion in childhood, or a spike-and-wave abnormality in the EEG. Moreover, the risk of recurrence is greatest in the first 24 months. In patients with two or three unexplained seizures, a far higher proportion, about 75 percent, have further seizures in the subsequent 4 years.
Seizures due to Underlying Medical Disease
Several diseases announce themselves by an acute convulsion. Here we focus on generalized medical disorders as causes of single and episodic seizures, in contrast to structural lesions of the brain that cause focal or generalized epilepsy.