Clinical features of febrile seizures and EEG findings were compared in patients who did and did not develop later afebrile seizures among six selected families and 59 family members with febrile convulsions examined at the Department of Clinical Neurological Sciences, University of Western Ontario, London, Ontario. All six probands developed epilepsy, 5 with temporal lobe epilepsy (TLE), after onset of febrile convulsions (FC). Of 59 family members with FC, 8 (13%) developed TLE within an average of 12 years after the first FC and 4 (7%) had other seizures. Of 213 family members without FC, only 1 had TLE. The mean duration of FC was 100+/-133 min in those with later TLE and 9+/-19 min in patients without TLE at prolonged follow-up (mean 32 years). The total number of FC, the number in one day, and age at onset did not differ significantly between groups. Of 27 patients with FC who had EEGs, 11 (41%) had epileptiform records and all but one had epilepsy. Neuropathological examination of resected temporal lobes from 5 of the patients with prolonged FC and TLE revealed mesial temporal sclerosis. 
COMMENT. The duration of the febrile convulsion was the most important determinant of the later development of epilepsy and epileptiform EEGs. This finding echoes previous publications showing that prolonged febrile convulsions and seizure discharges in the EEG are the most significant criteria of a poor prognosis . Millichap, JG. Febrile Convulsions. A monograph. New York, Macmillan, 1968). Epilepsy and recurrent afebrile seizures developed in 30% of patients with prolonged febrile seizures and in only 5% of patients with short convulsions of less than 20 min. The incidence of paroxysmal EEG tracings in children who developed epilepsy following FC was five times that observed in children with uncomplicated febrile convulsions. EEG abnormalities occurred in 36% of patients with pronged FC >20 min and in 10% of those having short FC <20 min duration.
Berg AT and Shinnar S, examining complex febrile seizures , found a strong correlation between prolonged duration of the FC and focal features, both in first and recurrent FC. Also, complex features tended to repeat, especially the prolonged duration, suggesting genetic or constitutional factors. The authors recommend that such children may be candidates for diazepam given at the onset of fever to abort the occurrence of a prolonged seizure. The following authors report a conflicting viewpoint, a not uncommon happening among authorities on this subject.
Knudsen FU et al, examining the long term outcome of prophylaxis for febrile convulsions , found that the prevention of new febrile convulsions by intermittent diazepam at the onset of fever offered no advantages over treatment with diazepam administered at the time of onset of a seizure. The long term prognosis in terms of subsequent epilepsy, neurological, motor, intellectual, cognitive, and scholastic ability was not influenced by the type of treatment applied in early childhood.