28th July 2023

Meningitis

Meningitis is caused by inflammation of the meninges. Infectious causes include bacteria, viruses, and mycobacteria. It can also be caused by malignancy. This section focuses on bacterial causes.

The classical meningitis triad is headache, fever and neck stiffness. It may also cause confusion, drowsiness, and other focal neurological signs and symptoms.

The most common causative organism of acute bacterial meningitis is Neisseria meningitidis (meningococcus), followed by Streptococcus pneumoniae (pneumococcus).

Meningococcal disease is usually rapid in onset, with symptoms progressing over hours, and may present as florid sepsis with the classical non-blanching petechial rash, which is diagnostic of this bacteria. The rash indicates meningococcus rather than being a feature of all meningitis. The pneumococcal disease may be more subacute over a few days, and a purpuric rash is absent.

The investigation of choice is lumbar puncture (LP). This should ideally be done before initiating antibiotic therapy, or the results may not be accurate. Contraindications include evidence of raised intracranial pressure (as LP can cause uncal herniation in this case), coagulopathy, and a rapidly involving rash. CT is generally done prior to LP, providing there is time to rule out any intracranial mass that can cause raised intracranial pressure, and is an absolute necessity if the patient has any risk factors for a mass or any clinical features suggesting one. If arranging these investigations leads to a significant delay in treatment (i.e. more than 6 hours), antibiotics should be first commenced.

The cerebrospinal fluid analysis helps confirm acute bacterial meningitis as it should show a (very) high neutrophil count, with high protein and low glucose compared to venous blood. Microscopy may also identify the organism.

First line treatment is with intravenous ceftriaxone (or chloramphenicol if there is an allergy history to beta-lactams). Steroids are also indicated for pneumococcal disease. In a non-inpatient setting, a single dose of intramuscular benzylpenicillin is recommended as empirical treatment in suspected bacterial meningitis if there is a delay in reaching a hospital.

Tracing for prophylaxis is only required for close household contacts of Neisseria meningitidis, for instance, those who share a room or young children. Acute bacterial meningitis is a notifiable disease independent of microbiological causes.

Meningitis with Listeria monocytogenes and Mycobacterium tuberculosis can cause lymphocytosis rather than neutrophilia on CSF analysis. Listeria causes invasive disease in groups with a risk factor, as outlined in the Gastrointestinal Infections section. Treatment is with high dose amoxicillin (or co-trimoxazole if penicillin allergic).