Febrile seizures

Clinical manifestations
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By Renée Shellhaas MD MS, Carol S Camfield MD, and Peter Camfield MD

In many cases, the febrile seizure is the first clear symptom of illness. The first febrile seizure is complex in approximately 25% of cases. About 75% of febrile convulsions are “simple.” In the National Collaborative Perinatal Project study of 55,000 infants, 1706 experienced a first febrile seizure and were followed to 7 years of age. Twenty-eight percent of the initial febrile seizures were “complex”: 4% focal, 8% prolonged greater than 15 minutes, and 16% with recurrence within 24 hours. A Todd paresis (transient focal post-ictal weakness) occurred in 0.4% (Nelson and Ellenberg 1978). In another prospective cohort study of first febrile seizures, 35% of 428 children had 1 or more features of a complex febrile seizure (Berg and Shinnar 1996). A retrospective study from Singapore reported similar findings (Lee and Ong 2004).

There is a bimodal distribution of febrile seizure duration: most are brief (82% lasting a mean of 3.8 minutes), whereas the remaining 18% constitute a seemingly separate population whose seizures last a mean of 39.8 minutes (Hesdorffer et al 2011). Prolonged febrile seizures are relatively uncommon, but concern about subsequent development of mesial temporal sclerosis and epilepsy prompted a multicenter study of the phenomenology and imaging findings in 199 affected children (median age 16 months; interquartile range 12 to 24 months). Cases were collected in several emergency departments, and they had a median status epilepticus duration of 70 minutes. Most of these febrile status epilepticus episodes were focal at onset (68%) and nearly all (98%) were convulsive seizures (Hesdorffer et al 2012). Prolonged postictal unconsciousness (greater than 30 minutes), although rare, has been associated with febrile seizures that are focal or last longer than 5 minutes (Okumura et al 2004).

In This Article

Introduction
Historical note and nomenclature
Clinical manifestations
Etiology
Pathogenesis and pathophysiology
Epidemiology
Prevention
Differential diagnosis
Diagnostic workup
Prognosis and complications
Management
References cited
Contributors