Meningitis refers to inflammation of the leptomeninges (pia and arachnoid). There are a number of different causes.
Infection is the most common cause and a viral cause the most common agent.
Base of skull fractures
Extremes of age
Bacterial There is a variation in the more common causative agents depending on the patient’s age. Neonatal:
Group B strep
H. Influenzae type B
H. Influenzae type B
Hospital acquired/post traumatic
Tuberculosis is also a potential agent, although the clinical picture is different from the other bacterial causes. It is more common in patients with HIV.
Mainly in immunosuppressed patients.
The classic triad of meningitis is that of:
The presentation will be dependent on the cause. Bacterial and viral causes generally produce an acute meningitis picture. Viral meningitis may be less severe in its presentation and more subacute in onset (1-7 days).
Common presenting features include:
Altered mental state
There may be risk factors present in the clinical history. This may help guide you to a more specific causative agent. Some cases may include coexisting encephalitis, meningoencephalitis, and so there may be the associated CNS features of this condition as well. In childhood, meningococcal disease may present in combination with sepsis.
There are some features of the clinical examination that can provide support to a diagnosis of meningitis.
Lying flat on back, hip and knee both flexed at 90 degrees
Knee is gradually extended
Provokes back pain
Lying flat on back
Neck is flexed
Results in hip and knee flexion
Head jolt accentuation test
Lateral head rotation worsens headache
There may be alterations of consciousness in severe cases. Focal neurological signs may also be present.
Many of these will be directed at the presenting complaint, as the diagnosis may not be immediately apparent, despite some distinguishing common features.
Important in presentation with altered consciousness
Additional investigations may be guided by suspicion of causative agent
India ink stain
TB investigation - large volume, ZN stain
An LP can confirm diagnosis. More specialised investigations may be subsequently required e.g. MRI, but are not very useful in the acute situation.
Notes on LP CSF interpretation are available here.
Treatment is usually started empirically due to the urgent nature of the condition. Even though a viral cause is more common, bacterial infection should be assumed in the first instance. Key specific components of treatment are:
Broad spectrum antibiotics with adequate CNS penetration are commenced for bacterial meningitis. Ceftriaxone is a common first line agent. Benzylpenicillin (or equivalent) should be given in cases of immunocompromised state when listeria needs to be covered for. More specific antimicrobial guidance can be provided once a causative agent is known. In cases where there may be different causative agents e.g. neurosurgical patient, different antibiotics may be needed and should be guided by microbiology.
Steroids (dexamethasone 0.15mg/kg QDS) are commenced with or before the first dose of antibiotics. Their role is to prevent meningeal injury from the resulting inflammatory response to bacterial death. There is some evidence of reduced complications and mortality rate from their administration (Cochrane 2013 review). This includes:
Trend to reduced mortality (in S Pneumoniae disease)
Reduced hearing loss (in children with H Influenzae)
Reduced short term neurological sequelae
Adults - give if suspected S Pneumoniae and can discontinue if not. Children - give prior to antibiotics and continue for 4 days
Viral Meningitis The management of viral meningitis is primarily supportive. Aciclovir is beneficial in HSV infections (if given very early) and should be commenced early if there is a consideration of HSV encephalitis.
Neisseria meningitidis infection has infection control implications because of the risk of transmission. Droplet precautions are needed in hospital. Close contacts of the patients are at risk and so require post exposure prophylaxis.
Epidemiology & Complications
It is more common in the young and elderly. Viral meningitis is the most common cause. Vaccination (e.g. HIB, meningitis C) is changing the epidemiology of the causative pathogens. There are about 6000 cases of meningitis reported each year in the UK, with a 50:50 viral:bacterial split, but it is felt that viral causes are significantly underreported. It is a notifiable condition in the UK.
Complications are usually related to bacterial disease, with viral meningitis generally having an excellent outcome. Complications include: Intracranial