Febrile Convulsions: The Pendulum Swings
Abstract & Commentary
Source: McDonald BK, et al. Febrile convulsions in 220 children—neurological sequelae at 12 years follow-up. Eur Neurol 1999;41:179-186.
Febrile convulsions (fc) are the most common seizure type in humans, occurring in some 2-5% of children aged 6 months to 6 years in U.S. and European populations and in perhaps as many as 6-9% in Asian populations. The simple view that FC are without long- term sequelae and without implication for future epilepsy is rapidly changing, along with the definition of genetic and environmental factors that are associated with this seizure type (Kugler SL, Johnson WG. Brain Dev 1998;20:265-274).
McDonald and associates examined the risk of development of future epilepsy in 220 children with a 12-year follow-up. This study was a component of the almost 20-year-old National General Practice Study of Epilepsy (NGPSE) in the United Kingdom, which prospectively follows 1195 patients of all ages from the time of first identified seizures. Maintenance of a registry among all general practitioners in the UK with a unique study identification number for each patient enables detailed long-term surveillance to be performed.
Of the 220 patients studied, 12 (5.9%) later developed recurrent unprovoked seizures (i.e., epilepsy) as compared to a general population lifetime incidence of 1.4%. Among the factors that seemed to be associated with increased 12-year risk of future epilepsy the presence of four or more FCs (odds ratio, OR =9.4, P = 0.015) seemed most clearly defined. Complex features, which McDonald et al consider as: 1) focal seizure at onset or post-ictally; 2) recurrent seizures during same febrile illness; or 3) convulsion lasting longer than 10 minutes, may presage future neurological deficit, but not epilepsy. For example, McDonald et al found that the presence of any complex feature does not significantly increase the 12-year risk of future epilepsy, but increases the risk of neurological deficits at 12-year follow-up by 5.1-fold (P = 0.0038). Other recent studies have stressed that focal complex febrile convulsions (CFC) may be of particular concern, with definite MRI abnormalities detected in six of 15 patients with focal CFC but in none of 12 patients with non-focal CFC (VanLandingham KE, et al. Ann Neurol 1998;43:413-426); however, it is not clear if the MRI abnormalities are causally related to convulsions.
COMMENTARY
What one would really want to know is the implication of febrile seizures on the lifetime risk of epilepsy. According to the McDonald et al study, the cumulative risk of epilepsy seems to continue to increase with length of follow-up: 1.4% by two years, 3.3% by five years, 5.2% by 10 years, and 6.0% by 12 years. The lifetime risk of epilepsy in a patient with FCs, if these results are extrapolated, would translate to a risk exceeding 20%. It may be possible to define subpopulations (such as patients with > 4 seizures, or with certain genetic predisposition) that will have higher lifetime risks. In any event, it is clear that long-term follow-up of patients will be needed in order to determine minimal estimates of total lifetime risk.
Do these results have any implication to the current expectant, do-little approach to the management of FCs? Not immediately, as McDonald et al point out. A 12-year increase in risk of epilepsy from about 1% to 6% probably does not warrant the risk of a 12-year exposure to any currently available anticonvulsant. However, if genetic and clinical factors can be better defined in order to clarify "febrile convulsion syndromes," there might be certain populations of patients with especially high lifetime risks in which the need for treatment could be reconsidered. —rt
The risk of epilepsy within 12 years after febrile convulsions in childhood:
a. is the same as in a patient without a history of febrile convulsions.
b. may be higher if there is a history of multiple (> 4) febrile convulsions.
c. does not seem to increase beyond the risk of epilepsy at five years of follow-up.
d. is much higher if the febrile convulsions have complex features.
e. is extremely similar to the risk of neurological deficits at 12-year follow-up.
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