Occasional seizures other than febrile convulsions may be associated with fever as a consequence of the causal disorder. However, the definition of febrile convulsions excludes infections of the CNS (see Chapter 14). The main causes are listed in Table 15.1.

The most common causes of symptomatic seizures with fever are meningitis and encephalitis, which amounted to 82 (62%) of the 133 patients of Ellenberg et al. (1984). Seizures with bacterial meningitis are significantly associated with a young age, a delay in diagnosis, a low serum sodium level, and evidence of infarction and/or ventricular enlargement on a computed tomographic (CT) scan (Snyder, 1984). A small proportion of seizures associated with purulent meningitis may be caused by the fever itself (Ounsted et al., 1985), and patients with meningitis may certainly present with simple febrile convulsions (Wallace, 1985; Ratcliffe and Wolf, 1977) without meningeal signs, especially in children younger than 18 months. Therefore, a lumbar puncture should be systematically considered in infants with febrile convulsions at younger than 18 months. However, Green et al. (1993) found that children with meningitis were usually obtunded or comatose; only 8 of their 523 patients had a normal level of consciousness, and only 47 (1.7%) of the 2,780 patients they reviewed had no meningeal signs. Seizures with fever in infants younger than 6 months should always raise the suspicion of CNS infection (Heijbel et al., 1980; Aicardi and Chevrie, 1970; Van den Berg and Yerushalmi, 1969).
In one series (Ellenberg et al., 1984), 25% of infants with symptomatic febrile seizures were younger than 6 months, whereas only 6.4% of those with true febrile convulsions were in that age group. The occurrence of seizures with bacterial meningitis has an unfavorable prognosis (Snyder, 1984), especially when the seizures are prolonged and focal. This is usually attributed to the complications responsible for the emergence of seizures. Some evidence, however, indicates that the convulsive activity itself may produce or favor brain damage (Ounsted et al., 1985). In the authors’ opinion, systematic anticonvulsant treatment from the onset of the illness is justified in all children younger than 4 years with bacterial meningitis, because seizures supervene in 10% to 40% of patients. Early diagnosis and treatment, as well as careful attention to electrolyte balance, could possibly decrease the incidence of this major complication.

Viral meningitis is probably a fairly common cause of symptomatic convulsions with fever. Rutter and Smales (1977) found three cases of viral meningitis in a series of 328 children with febrile convulsions who were submitted to systematic lumbar puncture. Only 1 of the 328 children had purulent meningitis. All types of encephalitis and meningoencephalitis can be responsible for seizures. Herpes simplex is the most common cause of encephalitis in Western Europe and the United States. Early diagnosis is important because this is a treatable condition. Seizures are often the first symptom, and they are an indication for performing lumbar puncture. The seizures are localized and often prolonged, and they are associated with neurologic signs and depression of consciousness that does not clear rapidly after the arrest of convulsions. Other viruses, especially herpesvirus 6 (and 7), may also produce encephalitis, which usually is of a lesser severity (Barone et al., 1995; Jones et al., 1994; Asano et al., 1992).

Dehydration associated with acute diarrheal disease was responsible for 15% of the symptomatic convulsions with fever in the series by Ellenberg et al. (1984). The seizures are usually attributed to electrolyte imbalance, particularly to that resulting from the rapid correction of hypernatremia (Plouin et al., 1979; Swanson, 1977; Hogan et al., 1969). This mechanism is probably not exclusive, and convulsions may also result from vascular collapse, which, at times, is associated with intracranial venous thrombosis (Aicardi and Goutières, 1973); from the action of bacterial toxins, particularly with shigellosis (Lahat et al, 1990) and salmonellosis; and from the fever itself (Lennox-Buchtal, 1973). A good correlation between the degree of fever and the incidence of convulsions has been reported (Mélékian et al., 1962), and at least some of the seizures that occur with febrile dehydration are probably true febrile convulsions. The seizures often present as status epilepticus, but various types may be encountered (Andrew, 1991; Plouin et al., 1979). Recently, a number of reports of clusters of seizures in infants that usually occur without fever in association with a mild gastroenteritis have been reported in infants (see Chapter 13).