Meningitis

 

• Background

  Inflammation of the meninges, the membranes surrounding the brain.

  Causes

  Commonest causes of bacterial meningitis by age:

  • <3 months: Group B Strep.
  • 3 months to 45 years: Neisseria meningitidis.
  • >45 years: Streptococcus pneumoniae (pneumococcal meningitis).
  • Other causes: Staph. aureus, E. coli, TB, H. influenzae (now very rare due to vaccination).
  • Listeria monocytogenes: may occur in pregnancy, neonates, the elderly, or alcohol misusers.

  Viral (aka aseptic) meningitis is slightly commoner than bacterial meningitis, though often mild and mistaken for flu. Pathogens:

  • Enteroviruses: coxsackie, echovirus.
  • Herpes simplex, HSV2 more than HSV1.
  • Mumps
  • Measles

  Fungal meningitis:

  • Usually Cryptococcus neoformans.
  • It has an insidious onset.

  Non-infectious:

  • Cancer: carcinomatous meningitis.
  • Drugs: co-amoxiclav, NSAIDs, IVIg, azathioprine.
  • Inflammatory and autoimmune: sarcoidosis, SLE, Behcet's.

  Epidemiology

  • 40% of cases of bacterial meningitis are in children aged <15 years.
  • Commonest in first few months of life, affecting 1/2000 per year, then incidence drops to around 1/100,000 per year for the rest of life.

  Meningococcal disease

  • Neisseria meningitidis is a Gram -ve diplococcus, which can cause meningitis (meningococcal meningitis) and/or disseminated infection (meningococcaemia). In many people, however, it is a normal inhabitant of the nasopharynx.
  • 90% of cases are due to serogroup B, as C is now prevented by vaccine. The new MenB vaccine is likely to change this.
  • Transmission: droplets from the upper respiratory tract. Incubation: 3-7 days. Most infectious before symptom onset.

• Signs and symptoms

  Symptoms:

  • Classic triad of meningitis: fever, stiff neck (can't place chin on chest) and headache or altered mental status. Present in 50%.
  • Other features: vomiting, photophobia, mottled skin, confusion, seizures, rigors, cold hands and feet.
  • Headache, stiff neck, and photophobia are symptoms of meningeal irritation (meningism), also seen in subarachnoid haemorrhage.

  Signs of meningism:

  • Kernig's sign: with hip and knee flexed, pain limits passive extension of the knee.
  • Brudzinski's sign: neck flexion leads to involuntary hip and knee flexion.
  • Both are around 10% sensitive and 90% specific for meningitis.

  Cerebral oedema:

  • May lead to ↓level of consciousness, papilloedema, and focal CNS signs.

  Meningococcaemia:

  • Petechiae and purpura: look carefully all over including backs of legs etc.
  • Septic shock: ↓BP, ↓capillary refill.
  • DIC

  Pneumonia may be present in pneumococcal meningitis.

  Viral meningitis:

  • Prominent headache.
  • Flu like syndrome.
  • Other features may be minimal or absent.

• Risk factors

  • Immunosuppression, including complement deficiencies and asplenia.
  • Skull fractures or anatomical defects.
  • Crowding: university halls, military barracks, Hajj (including N. meningitidis Y and W135 serogroups).

• Investigations

  Initial antibiotics should precede investigations in suspected meningitis.

  Bloods:

  • ↑WBC, ↑CRP.
  • U&Es and LFTs.
  • Blood culture ± N. meningitidis PCR.
  • Coag: DIC.

  Lumbar puncture:

  • CT and ophthalmoscopy first if ↑ICP suspected.
  • Bacterial CSF: ↑↑polymorphs , ↑protein, ↓glucose, bacteria on culture, gram stain. Listeria can be mixed polymorphs and lymphocytes.
  • TB CSF: ↑lymphocytes, ↑protein, ↓glucose, ZN stain +ve.
  • Viral CSF: ↑lymphocytes, viral PCR +ve.

  Other investigations:

  • Throat swab for N. meningitidis.
  • CXR: pneumococcal pneumonia, TB.

• Management

  Acute

  • Resuscitate, including O2 and fluids.
  • Broad-spectrum IV antibiotics stat e.g. cefotaxime. Add amoxicillin if age >50 years or <3 months to cover Listeria. Benzylpenicillin IM if pre-hospital (e.g. GP).
  • Dexamethasone IV if >3 months old: reduces neurological complications, but doesn't affect mortality.

  Public health measures

  • Notify public health authorities about any case of meningitis or meningococcaemia.
  • Isolate patient.
  • Prophylactic antibiotics: single dose of ciprofloxacin or 2 days of rifampicin. Give to all close contacts from the last 7 days, regardless of vaccination status; includes household contacts, household-type contacts (boy/girlfriends, students sharing kitchen, pupils in same dormitory), or healthcare workers with large exposures e.g. during intubation.
  • Further cases are most likely to present in the 7 days after the 1st.

  Infectious clusters:

  • Defined as ≥2 cases in the same setting within 4 weeks.
  • Prophylactic antibiotics to those at risk or the whole institution.
  • If MenC is the cause, vaccinate all except those with vaccine in the past 1 year. If MenA/W135/Y is the cause, give the quad ACWY vaccine.

• Complications and prognosis

  • Short term: ↑ICP, shock, DIC, subdural effusions, SIADH, seizures, venous sinus thrombosis.
  • Long-term: cranial nerve palsies, deafness, limb amputation (in meningococcal disease), memory or cognitive problems (25%).
  • Mortality: 5% in meningococcal, 25% in pneumococcal, 35% for listeria.

• Lumbar puncture (LP)

  Indications

  • Meningitis, encephalitis.
  • Sub-arachnoid haemorrhage.
  • Multiple sclerosis.
  • Cancer: neoplastic meningitis, medulloblastoma.

  Contraindications

  • ↑ICP, including signs such as: focal neurology, severe headache, ↓level of consciousness, vomiting, papilloedema.
  • Coagulopathy.
  • Cardiorespiratory compromise.

  Procedure

  1. Patient lies on their left side, with their back to the edge of the bed, and knees fully flexed to chin. Alternatively, they can be sat up with their hand resting on a table in front.
  2. Mark (e.g. with a nail print) the L3/4 area, in line with the iliac crests.
  3. Wash hands and sterilize site with iodine.
  4. Inject lidocaine and wait 60 seconds.
  5. Insert an atraumatic needle (22G), withdraw stilette, and measure the opening pressure.
  6. Collect the sample in 3 bottles.
  7. Remove the needle, re-insert the stilette, and dress the site.

  Complications

  • Post-LP headache (30%). Reduced by use of atraumatic (noncutting) needle and re-insertion of needle stilette before needle withdrawal.
  • Infection
  • Nerve damage. Extremely rare. Brushing past a nerve, causing pain/sensation in the leg, is commoner.