Approach
The diagnosis is made through clinical assessment; however, as ruling out meningitis often drives the approach, related tests may take precedence. Infants who present with a suspected febrile seizure under the age of 6 months require particularly careful medical evaluation.
History
The patient tends to be young (age 3 months to 5 years, most commonly 12 to 24 months), male, and presenting with a fever that is followed soon after by loss of consciousness and generalised clonic movements and/or tonic stiffening. The seizure is commonly short in duration (3 to 5 minutes) and recovery of consciousness rapid, without sequelae. The degree of fever is generally high. Often there is a family history of febrile seizures. A seizure that is focal, lasts >15 minutes, or is repeated within a 24-hour period is classified as a complex febrile seizure.
Fever aetiology
A viral infection is generally suspected, with upper respiratory tract symptoms, otitis media, or gastroenteritis. A typical erythematous maculopapular rash of exanthem subitum (roseola, sixth disease), human herpesvirus-6 infection, or an epidemic of influenza A may define the cause more specifically. In practice, the virus is not usually identified. Rapid simple methods of viral detection are emerging that may allow early diagnosis and the use of antiviral agents. Bacteraemia is rare, but meningitis should always be considered.[41]
Physical signs consistent with diagnosis
Physical signs are as follows: extracranial infection and fever (e.g., upper respiratory infection, otitis media, gastroenteritis); rapid recovery of consciousness after seizure (within 30 minutes); and absence of nuchal rigidity and focal neurological abnormalities.
Exclusion of meningitis
Lumbar puncture (LP) is indicated to rule out meningitis or encephalitis if: presence of suspicious symptoms and signs (e.g., bulging fontanelle, nuchal rigidity) and if age is <12 months (signs of meningitis are often absent in this age group);[1] a focal, prolonged, or multiple seizure occurs within 24 hours with prolonged impairment of consciousness; or there is history of persistent irritability or lethargy, or pre-treatment with oral antibiotics (prior antibiotic treatment can mask meningitis, and therefore performing a LP should be given consideration in this setting). There is no evidence, however, to support routine LP in all children admitted with a simple febrile seizure, especially when typical clinical signs of meningitis are lacking.[42][43]
A meta-analysis showed that in children with an apparent simple febrile seizure, the average prevalence of bacterial meningitis was 0.2% (range 0% to 1%). The pooled prevalence of bacterial meningitis among children with an apparent complex febrile seizure was 0.6% (95% CI 0.2 to 1.4).[44] Another multi-centre cohort study of children presenting with a complex febrile seizure found rates of bacterial meningitis and herpes simplex encephalitis were 0.7% and 0%, respectively.[45]
According to the American Academy of Pediatrics (AAP), the potential risks associated with LP are outweighed by the benefits. It should be noted that the AAP proposed modifications of the 1999 guidelines, in response to critical appraisal in the literature, and these have generally been accepted by the profession.[1] Some authorities, especially consultants in paediatric emergency medicine, have questioned the justification for recommendations based on age. Some difference of opinion remains regarding LP in younger children with suboptimal immunisation status for their age. UK guidelines state that the experience of the practitioner and the infant's age (<1 year) are important in judging the need for LP.[46] The AAP recognises that clinical skills vary between examiners and recommends a conservative approach with emphasis on the diagnostic value of the LP. A previously normal result on LP does not rule out meningitis in a child whose clinical condition deteriorates subsequently. In practice, the AAP guidelines are not strictly followed and should not replace clinical judgement.[2][47][48]
Tests
A simple febrile seizure does not usually require further evaluation such as electroencephalography, neuroimaging, or other studies.
However, meningitis should be considered in the differential diagnosis for any febrile child.[49][50]
Lumbar puncture is the key test to rule out meningitis or encephalitis. An electroencephalogram (EEG), computed tomography scan, or magnetic resonance imaging (MRI) scan is unnecessary after a first febrile seizure.[1][51]
EEG and MRI may be helpful in diagnosis with recurrence of complex febrile seizures, prolonged impairment of consciousness after seizure (>60 minutes), or abnormal neurological signs; however, a Cochrane review found no evidence to support or refute the use of EEG and its timing after complex febrile seizures among children under the age of 5 years.[52][53] A neurologist should be consulted in these cases.
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
Laboratory evaluations
Serum electrolytes, full blood count, and blood glucose tests are not routinely recommended, but may be required to determine the cause of fever.[1] Check capillary blood glucose for hypoglycaemia. If there is prolonged postictal impaired consciousness or vomiting and ketosis, electrolyte levels may be indicated. Calcium, phosphorus, and magnesium levels are unnecessary. Viral studies may be useful in patients with complex febrile seizures and symptoms of encephalitis or encephalopathy.
How to take a venous blood sample from the antecubital fossa using a vacuum needle.
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