What are the guidelines for lumbar puncture and diagnostic workup in pediatric patients presenting with febrile seizures, particularly in those under 12 months old or with signs of meningismus?

Guidelines for Lumbar Puncture and Diagnostic Workup in Febrile Seizures

Lumbar puncture should almost always be performed in children under 12 months of age presenting with febrile seizures, and should probably be performed in those 12-18 months old, while children over 18 months require LP only if specific high-risk features are present. 1

Age-Based Approach to Lumbar Puncture

Infants Under 12 Months

• LP is almost always indicated because meningeal signs are extremely difficult to detect reliably in this age group 1, 2
• The inability to assess for meningismus clinically in young infants makes LP the only reliable method to exclude bacterial meningitis 3
• Recent research challenges universal LP in this age group if the seizure is simple and clinical examination is completely normal, but guidelines remain more conservative 4

Children 12-18 Months

• LP should probably be performed, though clinical judgment regarding meningeal signs becomes more reliable 1, 2
• The decision can be individualized based on vaccination status (Haemophilus influenzae type b and Streptococcus pneumoniae), presence of any concerning features, and ability to ensure close follow-up 4

Children Over 18 Months

• LP is indicated only when specific high-risk features are present 1

Absolute Indications for Lumbar Puncture (Any Age)

Perform LP immediately if any of the following are present:

• Clinical signs of meningism (neck stiffness, positive Kernig's or Brudzinski's sign, bulging fontanelle) 1, 5, 4
• Complex seizure features: prolonged (>15 minutes), focal, or multiple seizures within 24 hours 1, 5, 4
• Altered mental status: child is unduly drowsy, excessively irritable, or has impaired consciousness lasting >1 hour after the seizure 1, 5, 4, 3
• Systemically ill appearance or septic signs 1, 5, 4
• Incomplete recovery within one hour of seizure 1
• Prior antibiotic treatment (may mask meningitis symptoms) 4, 3, 6

Essential Diagnostic Workup

Immediate Bedside Assessment

• Measure blood glucose with glucose oxidase strip in any child still convulsing or unrousable 1, 7
• Document temperature, seizure characteristics (duration, focal vs. generalized), and time to return to baseline 1

Routine Investigations NOT Required

• No routine investigations are necessary in most children after a simple febrile seizure 1
• EEG is not indicated after a first simple febrile seizure, as it does not guide treatment or predict prognosis 1, 7
• Routine blood work (electrolytes, calcium, blood urea) is not recommended for simple febrile seizures 1, 7
• Neuroimaging (CT or MRI) should be reserved for complex seizures lasting >20 minutes or when focal neurological deficits persist 1

When to Consider Additional Testing

• Urinalysis and urine culture should be obtained in young children (particularly males under 2 years) to identify urinary tract infection as the fever source 8
• Blood cultures if the child appears septic or systemically ill 1

Critical Safety Considerations

Before Performing Lumbar Puncture

• Assess for signs of increased intracranial pressure (coma, papilledema, focal neurological deficits) 1
• A comatose child must be examined by an experienced physician before LP due to risk of herniation 1
• Brain imaging may be necessary before LP if increased intracranial pressure is suspected 1

Timing and Reassessment

• If the decision is made not to perform LP, the physician must be prepared to reassess within a few hours 1
• Early clinical re-evaluation (at least 4 hours after initial assessment) is particularly helpful in infants under 12 months 5

Common Pitfalls to Avoid

• Do not dismiss the need for LP in infants under 12 months based solely on a "simple" seizure presentation—meningitis can present atypically in this age group 2, 3
• Do not delay LP when indicated; bacterial meningitis requires urgent diagnosis and treatment to prevent mortality and morbidity 1, 4
• Do not perform unnecessary investigations (EEG, extensive metabolic panels) in straightforward simple febrile seizure cases, as they do not change management 1, 7
• Do not assume prior antibiotics rule out meningitis—this is actually an indication for LP as antibiotics may partially treat and mask meningitis 4, 3, 6

Evidence-Based Risk Stratification

Research demonstrates that children with simple febrile seizures (generalized, <15 minutes, single episode in 24 hours) who have a completely normal clinical examination have an extremely low risk of bacterial meningitis (0-3.6%) 4, 9. However, the presence of any complex features or concerning clinical signs significantly increases this risk to 14-36% 4, 3.

The incidence of bacterial meningitis in febrile seizure populations ranges from 1.9-4.7%, with all cases having identifiable risk factors on clinical examination 4, 3. This supports a selective rather than universal approach to LP in older children, but the conservative age-based guidelines remain the standard of care to prevent missed diagnoses in vulnerable infants 1, 2.