Any viral or bacterial illness, or, rarely, an immunization, may be the precipitant of the fever; herpesvirus 6 is one of the common precipitants, probably because of its tendency to cause high fever. Prophylactic antiepileptic drugs have not been found to be helpful in preventing febrile seizures. Except for a presumed genetic relationship with benign epilepsy of childhood (Luders et al), which in itself is transient in nature, these patients’ risk of developing epilepsy in later life is only slightly greater than that of the general population. In some families, such as those studied by Nabbout and colleagues, febrile seizures alone, without generalized epilepsy, have been associated with a particular gene by linkage analysis. Presumably, when the gene products are identified, some insight into the nature of defects that lower the seizure threshold will be forthcoming.
This benign type of febrile seizure should not be confused with more serious illnesses in which a febrile acute encephalitic or encephalopathic state causes focal or prolonged seizures, generalized or focal EEG abnormalities, and repeated episodes of febrile convulsions during a febrile illness (complex febrile seizures). In these cases, these seizures may recur not only with infections but also at other times. When patients with both types are combined together under the rubric of febrile convulsions, it is not surprising that a high percentage are complicated by later atypical petit mal, atonic, and astatic spells followed by tonic seizures, mental retardation, and partial complex epilepsy. In a study of 67 patients with medial temporal lobe epilepsy by French and colleagues, 70 percent had a history of complex febrile seizures during the first 5 years of life, although many did not again develop seizures until their teens. Bacterial meningitis was an important risk factor; head and birth trauma were less-common factors. Epidemiologic studies have substantiated this clinical point of view. Annegers and colleagues observed a cohort of 687 children for an average of 18 years after their initial febrile convulsion. Overall, these children had a fivefold excess of unprovoked seizures in later life. Among the children with simple febrile convulsions, the risk was only 2.4 percent. By contrast, children with what Annegers and colleagues called complex febrile convulsions (focal, prolonged, or repeated episodes of febrile seizures) had a greatly increased risk—8, 17, or 49 percent, depending on the association of one, two, or three of the complicating features.
It has been appreciated for a long time that seizures can be evoked in certain individuals by a discrete physiologic or psychologic stimulus. The term reflex epilepsy is reserved for this small subgroup. Forster classified these seizures in accordance with their evocative stimuli into five types: (1) visual—flickering light, visual patterns, and specific colors (especially red), leading to rapid blinking or eye closure; (2) auditory—sudden unexpected noise (startle), specific sounds, musical themes, and voices; (3) somatosensory—either a brisk unexpected tap or sudden movement after sitting or lying still, or a prolonged tactile or thermal stimulus to a certain part of the body; (4) writing or reading of words or numbers; and (5) eating.
Visually induced seizures are by far the most common type. The seizures are usually myoclonic but may be generalized and triggered by the photic stimulation of television or an EEG examination or by the photic or pattern stimulation of video games. In other types of reflex epilepsy, the evoked seizure may be focal (beginning often in the part of the body that was stimulated) or generalized and may take the form of one or a series of myoclonic jerks or of an absence or tonic-clonic seizure. Seizures induced by reading, voices, or eating are most often of the complex partial type; seizures induced by music are usually myoclonic, simple, or complex partial. A few such instances of reflex epilepsy have been caused by focal cerebral disease, particularly occipital lesions.