Meningitis

Meningitis refers to inflammation of the meninges, which are the membranes which cover the brain.

Causes

Meningitis can be caused by bacteria, viruses, fungi, parasites and other non-infectious processes such as autoimmune conditions.

• Bacterial
  • Streptococcus pneumoniae (pneumococcus)
  • Neisseria meningitides – subtypes B, C, Y and W (meningococcus)
  • Haemophilus influenzae
  • Mycobacterium tuberculosis, which causes tuberculous meningitis
  • Staphylococcus aureus
• Viral
  • Enteroviruses
  • Varicella zoster virus
  • Herpes simplex virus 1 and 2
  • Mumps
• Fungal
  • Less common - usually occur in immunocompromised patients
  • Cryptococcus neoformans
• Parasitic
  • Amoeba
  • Toxoplasmosis gondii
• Non-Infective
  • Malignancy
  • Sarcoidosis
  • SLE

Pathophysiology

• Bacteria can either directly enter into the cerebrospinal fluid (CSF) through nearby anatomical structures such as the middle ear, during operative procedures or from foreign objects.
• Alternatively, there may be haematogenous spread of bacteria, for example, entering the blood stream through mucosal invasion of the nasopharynx, and then reaching the subarachnoid space.
• Similarly, viruses can also spread via the haematogenous route, or from retrograde spread from a nerve ending.

Clinical Features

• Fever and rigors due to infection
• Meningeal irritation, characterised by:
  • Headache
  • Photophobia
  • Neck stiffness
• Non-blanching petechial rash: A sign of meningococcal septicaemia
• Brudzinski’s sign: Flex the neck -> involuntary flexion of the hip and knee
• Kernig’s sign: Flex the hip and knee at 90 degrees and then slowly extend the knee. Positive test if there is pain.
• Signs of raised intracranial pressure
  • Headache
  • Vomiting
  • Papilledema
  • Reduced Glasgow Coma Scale (GCS)

• Seizures
• Septic features: Hypotension, tachycardia, oliguria

Differential Diagnosis

• Different types of meningitis: Viral/bacterial/tuberculous/fungal
• Encephalitis: Inflammation of the brain parenchyma
• Cerebral venous sinus thrombosis: A clot in a dural venous sinus
• Cerebral abscess: Collection of pus within the brain which can act as a space-occupying lesion
• Tension type headache: Can cause neck pain but the nature of the pain is likely to be much milder than suspected meningitis

Investigations

Bedside Tests

• Observations: Important particularly in monitoring signs of sepsis (pyrexia, tachycardia, hypotension)
• Neurological examination, including GCS
   

Bloods

• FBC: Raised white cells
• U&E, LFTs, Clotting: Baseline
• CRP/ESR: Raised
• Blood cultures
• Blood glucose: To compare CSF glucose with
• VBG/ABG: Signs of sepsis i.e. ?lactic acidosis
• Whole blood PCR for N meningitidis

Imaging

• Chest x-ray: Checking for pre-existing pulmonary tuberculosis
• CT/MRI Head: Rule out other intracranial pathologies
   

Special Tests

• Lumbar puncture: Contraindicated in cerebral abscess or raised intracranial pressure!
• India ink staining of CSF: this allows checking of cryptococcus
• CSF culture for tuberculosis although this will take time

Management

Bacterial Meningitis

Bacterial meningitis requires administration of antibiotics urgently, and investigations e.g. lumbar punctures should never delay administration of antibiotics.

Community Management

• Urgent transfer to secondary care
• Urgent IV/IM benzylpenicillin

Secondary Care Management

• Empirical Management: Remember you won't know what a patient has until all the cultures and CSF etc come back so you need empirical treatment in the first instance. This is usually with Ceftriaxone + Dexamethasone. 
  • Patients with penicillin allergy might be given IV chloramphenicol instead as patients with penicillin allergies can have cross-reactivity with cephalosporins
• Children and young people >3 months of age: IV Ceftriaxone
• Children <3 months: IV Ceftriaxone + Amoxicillin/Ampicillin (this covers Listeria)
• Group B streptococcal meningitis (a common cause of meningitis in neonates): IV Cefotaxime

Additional treatments involve:

• IV dexamethasone is also used in treatment
• Supportive treatment is usually required e.g., fluid resuscitation, analgesia
• ITU Involvement: If patients are extremely unwell and would benefit from ITU input

Viral Meningitis

Viral meningitis is usually self-limiting, but aciclovir can be used in management.

Tuberculous Meningitis

Managed with anti-tuberculous drugs.

Post Exposure Prophylaxis

The BNF recommends the use of either ciprofloxacin, rifampicin or IM ceftriaxone for post-exposure prophylaxis with meningococcal meningitis.

Complications

• Cerebral infarction: The leptomeningeal arteries passing through the infected parts of the meninges can become inflamed, which can cause obstruction and thus cerebral infarction
• Cerebral abscess
• Hydrocephalus: Pus can form between the meningeal layers, leading to adhesions which can then obstruct the free flow of CSF.
• Cranial nerve damage: Disruption of cranial nerves by adhesions
• Sensorineural hearing loss
• Sepsis
• Epilepsy

References

https://patient.info/doctor/cerebrospinal-fluid

https://spiral.imperial.ac.uk/bitstream/10044/1/34658/2/1-s2.0-S0163445316000244-main.pdf

https://ep.bmj.com/content/105/1/46 

https://www.nice.org.uk/guidance/cg102/chapter/Recommendations#bacterial-meningitis-and-meningococcal-septicaemia-in-children-and-young-people-symptoms-signs