Meningitis

Meningitis is inflammation of the meninges, most commonly caused by bacterial or viral infection. It is a medical emergency. Bacterial disease can deteriorate rapidly, causing death and significant neurological sequelae.

The interval to appropriate antimicrobial treatment correlates directly with outcome. Prompt recognition and immediate empirical treatment before diagnostic confirmation are the central principle of management.

Aetiology by age and risk group

• Neisseria meningitidis and Streptococcus pneumoniae account for the majority of community acquired bacterial meningitis in adults and older children
• Haemophilus influenzae type b is now uncommon in vaccinated populations
• Listeria monocytogenes is an important cause in neonates, adults over fifty and immunocompromised patients
• Group B streptococcus and Escherichia coli are the predominant causes in neonates

Viral meningitis, most commonly caused by enteroviruses, is generally self limiting. It is considerably more common overall than bacterial disease.

Fever, headache, neck stiffness and photophobia constitute the classical triad plus associated symptom. The complete combination is present in only a minority of confirmed cases.

Presentations are often atypical or non specific in the very young and the elderly, and should not be dismissed. Examples are irritability, lethargy and poor feeding in infants, and confusion and reduced consciousness in the elderly.

A non blanching purpuric or petechial rash is a specific and highly concerning sign of meningococcal disease with associated septicaemia. Give antibiotics immediately, without delay for investigation.

Kernig sign (pain and resistance on knee extension with the hip flexed) and Brudzinski sign (involuntary hip and knee flexion on passive neck flexion) support the diagnosis clinically. Sensitivity is limited, and their absence does not exclude meningitis.

Signs of raised intracranial pressure (declining consciousness, papilloedema, bradycardia with hypertension, focal neurological deficit) and signs of septic shock (hypotension, poor peripheral perfusion, tachycardia) indicate severe disease. Resuscitate immediately alongside specific treatment.

Take blood cultures immediately, before or simultaneously with antibiotic administration. Never delay antibiotics for this or any other investigation once bacterial meningitis is suspected clinically.

Lumbar puncture with cerebrospinal fluid analysis confirms the diagnosis and distinguishes bacterial from viral aetiology. Send for opening pressure, cell count and differential, protein, glucose with paired plasma glucose, Gram stain, culture, and polymerase chain reaction for specific organisms including meningococcus, pneumococcus and herpes simplex virus.

Bacterial meningitis typically shows a markedly raised neutrophil predominant white cell count, raised protein and low glucose relative to plasma. Viral meningitis typically shows a lymphocyte predominant picture, generally normal glucose and less markedly raised protein.

Computed tomography of the head before lumbar puncture is indicated where there are focal neurological signs, significantly reduced consciousness, papilloedema, new onset seizure, or immunocompromise. The concern is cerebral herniation if a significant mass lesion or raised intracranial pressure is present.

Imaging should not delay antibiotics. Give them immediately after blood culture collection, regardless of the timing of subsequent lumbar puncture.

Full blood count, C reactive protein, coagulation screen, glucose and blood gas (including lactate) support assessment of severity and the presence of associated septicaemia or disseminated intravascular coagulation.

Give empirical antibiotics immediately on clinical suspicion of bacterial meningitis. Do not wait for lumbar puncture or any other confirmatory investigation, because treatment delay is directly related to mortality.

Standard empirical treatment for adults and children beyond the neonatal period is ceftriaxone 2 g intravenously twice daily (or cefotaxime 2 g intravenously every 6 hours). Add vancomycin where there is concern for cephalosporin resistant pneumococcus according to local resistance patterns. Give a loading dose of 25 to 30 mg per kg, then maintenance dosed to a target trough of 15 to 20 mg per litre.

Add amoxicillin 2 g intravenously every 4 hours (or ampicillin at the equivalent dose) to the cephalosporin for patients over fifty, and for neonates, pregnant women and immunocompromised patients of any age. This covers Listeria monocytogenes, which is intrinsically resistant to cephalosporins.

Neonatal meningitis is treated with amoxicillin or ampicillin together with a third generation cephalosporin. Cefotaxime is generally preferred over ceftriaxone in neonates, given a lower risk of biliary sludging and kernicterus displacement. Adjust doses for postnatal age and weight. An aminoglycoside may be added according to local neonatal protocols.

Dexamethasone 10 mg intravenously every 6 hours for 4 days is recommended for adults with suspected or confirmed bacterial meningitis. Give it with or just before the first dose of antibiotic. Evidence shows reduced mortality and neurological sequelae, particularly for pneumococcal disease. Children receive the equivalent weight based dose (0.15 mg per kg every 6 hours).

Penicillin allergic patients require alternative regimens under specialist microbiology guidance. These typically incorporate chloramphenicol. For severe or anaphylactic penicillin allergy, other agents are selected according to the organism once identified.

Duration of treatment is guided by the confirmed or presumed organism: typically 7 days for meningococcal meningitis, 10 to 14 days for pneumococcal meningitis, and 21 days for Listeria monocytogenes, which tends to relapse with shorter courses.

Close contacts of confirmed meningococcal meningitis require chemoprophylaxis. Give household and other close contacts ciprofloxacin 500 mg orally as a single dose (or rifampicin 600 mg twice daily for 2 days, or ceftriaxone 250 mg intramuscularly as a single dose in pregnancy).

Notify public health authorities. The disease is mandatorily reportable and can cause cluster transmission.

Viral meningitis, once bacterial disease has been reasonably excluded, is managed supportively with analgesia, antipyretics and adequate hydration. The course is generally self limiting. Specific antiviral treatment is not needed in the great majority of enteroviral cases.