Meningitis
Meningitis is inflammation of the meninges, the membranes surrounding the brain and spinal cord, most commonly infectious (bacterial, viral, tuberculous, or fungal, each covered in further detail in their own dedicated entries) but occasionally non-infectious (drug-induced, malignant, or autoimmune).
This entry provides the general framework for recognition, workup, and initial approach; see the Meningococcal Meningitis, Haemophilus Meningitis, Neonatal Meningitis, Viral Meningitis, and Tuberculous Meningitis entries for pathogen-specific detail.
The classic triad of fever, neck stiffness, and altered mental status is present in only a minority of adult cases when all three are required simultaneously, and its absence should never be used to exclude the diagnosis, particularly in the very young, elderly, or immunocompromised, where presentation is frequently atypical or subtle.headache, photophobia, nausea and vomiting, and, in more severe or advanced disease, seizures and focal neurological deficits are common accompanying features.
Kernig's sign (pain and resistance on passive knee extension with the hip flexed) and Brudzinski's sign (involuntary hip and knee flexion on passive neck flexion) support the diagnosis when present but have limited sensitivity and should not be relied upon to exclude meningitis if negative.
A non-blanching petechial or purpuric rash strongly suggests meningococcal disease specifically (see that entry) and should prompt immediate empirical treatment without any diagnostic delay.
- Lumbar puncture with CSF analysis is the definitive diagnostic investigation, assessing opening pressure, cell count and differential, protein, glucose (paired with a simultaneous serum glucose for comparison), Gram stain, and culture, with the specific pattern helping distinguish bacterial (neutrophilic pleocytosis, elevated protein, low CSF:serum glucose ratio, typically under 0.4) from viral (lymphocytic pleocytosis, normal or mildly elevated protein, normal glucose) causes, though overlap and atypical patterns occur, particularly early in the illness course or with partially treated bacterial meningitis
- CT head before lumbar puncture is indicated where there are specific risk factors for raised intracranial pressure or an alternative structural cause (focal neurological deficit, papilledema, new-onset seizure, significantly reduced GCS, or immunocompromise) given the risk of coning with LP in this context, but should not delay empirical antibiotic administration, which should be given first if there is any anticipated delay to LP
- Blood cultures should always be taken, ideally before antibiotics if this causes no meaningful delay, given a meaningful proportion of cases have positive blood cultures even where CSF culture is negative or LP is delayed or contraindicated
- PCR-based multiplex meningitis/encephalitis panels, where available, offer rapid, sensitive pathogen identification across a broad range of bacterial and viral causes simultaneously
- Empirical antibiotics should be given immediately on clinical suspicion, without waiting for LP or imaging if either would cause meaningful delay (a widely used benchmark is within 1 hour of presentation): a commonly used adult empirical regimen is IV ceftriaxone 2 g bd, with IV amoxicillin/ampicillin 2 g every 4 hours added in those at risk of Listeria monocytogenes (age over 50, pregnancy, immunocompromise, alcohol use disorder), since cephalosporins do not reliably cover Listeria
- Dexamethasone (10 mg IV qds in adults, or 0.15 mg/kg IV every 6 hours in children), given with or just before the first antibiotic dose, is recommended for suspected or confirmed bacterial meningitis given evidence of reduced neurological sequelae, most robust for pneumococcal and Haemophilus meningitis specifically, and generally continued for 4 days if bacterial meningitis is confirmed, stopped if an alternative or non-bacterial cause is subsequently identified
- Once a specific organism is identified, antibiotic therapy is rationalized per organism and sensitivity (see the Meningococcal Meningitis and Haemophilus Meningitis entries for pathogen-specific detail)
- Supportive care includes careful fluid management (avoiding both hypovolemia and excessive fluid administration given the risk of cerebral edema), seizure management if present, and close neurological observation for signs of raised intracranial pressure or evolving complications (hydrocephalus, cerebral abscess, venous sinus thrombosis)
- Public health notification is required for confirmed or strongly suspected bacterial meningitis in most jurisdictions, given the outbreak potential of certain causative organisms (see Meningococcal Meningitis entry specifically)
Referral: this is a medical emergency requiring immediate infectious disease and, where relevant, neurology or neurosurgery involvement; ICU for reduced consciousness, seizures, or hemodynamic instability.
