Meningitis and encephalitis: Viva

Branch 1: Recognising the time-critical problem

The candidate should immediately recognise that this child has a fever with altered consciousness and a new seizure, which places bacterial meningitis and encephalitis jointly at the top of the differential. The presence of confusion and drowsiness, rather than isolated headache and neck stiffness, is the feature that shifts the working diagnosis towards encephalitis or meningoencephalitis alongside meningitis. [3]

The candidate should state that any febrile child with altered consciousness or a new seizure must be presumed to harbour a central nervous system infection until proven otherwise. The first priority is resuscitation and empiric treatment covering both bacterial meningitis and herpes simplex encephalitis, because the cost of waiting for definitive tests is irreversible brain injury. [1]

Branch 2: Investigations and the lumbar puncture decision

The candidate should outline blood culture, full blood count, C-reactive protein, glucose, and electrolytes drawn on cannulation. The definitive investigation is lumbar puncture with cerebrospinal fluid sent for cell count and differential, glucose with simultaneous blood glucose, protein, Gram stain, culture, viral polymerase chain reaction including herpes simplex, and bacterial polymerase chain reaction for meningococcus and pneumococcus. [3]

The examiner will probe the timing of lumbar puncture. Because this child is confused and had a new-onset seizure, he has an indication for neuroimaging before lumbar puncture. The candidate must state that neuroimaging and lumbar puncture never delay the first dose of antibiotics and aciclovir, which are given immediately on intravenous access. A normal computed tomography scan does not exclude raised pressure, so the decision to tap rests on clinical stability. [1]

Branch 3: Empiric therapy and the encephalitis decision

The empiric regimen for a child of this age is cefotaxime 50 mg per kilogram intravenously 6-hourly or ceftriaxone 50 to 100 mg per kilogram intravenously daily, combined with vancomycin 15 mg per kilogram intravenously for penicillin-resistant pneumococcus. Because encephalitis is plausible, add aciclovir 20 mg per kilogram intravenously 8-hourly without waiting for the cerebrospinal fluid herpes simplex polymerase chain reaction result. [2]

The candidate should justify the dexamethasone decision. Dexamethasone 0.15 mg per kilogram intravenously given with or just before the first antibiotic dose reduces hearing loss in Haemophilus influenzae type b meningitis with probable benefit in pneumococcal disease, but the benefit is lost once antibiotics have been given. When the diagnosis is unclear, many units give the dose empirically because the downside is small. [1]

When the cerebrospinal fluid returns a lymphocytic pleocytosis with a positive herpes simplex polymerase chain reaction, continue aciclovir for 14 to 21 days and arrange magnetic resonance imaging and electroencephalography to define the extent of temporal and frontal lobe involvement. Counsel the family that outcome depends on how early aciclovir was started and that structured developmental and neuropsychological follow-up is essential. [3]