Meningitis

Key facts:

Authors: Katharine Elliott and Andrew Stein
Top Tips: Absence of meningism does not exclude meningitis. In severe cases (eg meningococcal septicaemia), there may be no meningism. If hypotensive, call ITU immediately

Key Differential Diagnoses

• SAH
• Migraine (commonest alternative diagnoses)
• Encephalitis (can have both)
• Cerebral vein thrombosis (rare but important)

Key Investigations

• FBC, ESR, CRP
• U+E, LFT, Glucose
• Coagulation screen
• ECG, CXR
• BC, LP (± CT)

Key Treatment

• IV CEFTRIAXONE 2g od immediately (before LP ± CT)
• ± IV ACICLOVIR 10 mg/kg tds, if encephalitis possibility (especially if cerebral irritation)

Key Management Decision

• ?CT, before LP (do not wait for either before starting Rx)

Background

Acute meningitis is a medical emergency that requires rapid diagnosis and treatment

Introduction

• Meningitis is inflammation of the meninges of the brain or spinal cord. It is often infectious
• Meningitis may become evident over hours or days (acute) or a longer period (subacute or chronic. Whatever the onset, make sure the referring doctor (eg, GP or paramedic) gives IV ANTIBIOTICS (BENZYLPENICILLIN or CEFTRIAXONE) as soon as possibility is raised
• 60% are community-acquired. Meningococcus is carried in the nasopharynx often asymptomatically (carriers) and tends to produce epidemics in children and young adults. Incubation period 1-3 days. Beware partially treated cases (see below)
• Classical meningitis symptoms (headache, neck stiffness and photophobia) are not alwsy present
• Eg, the elderly may have nonspecific symptoms (eg, confusion with or occasionally without fever). Meningeal signs may be absent or mild
• Look for sources of meningitis eg CXR (lung abscess) and Skull XR (recent trauma?)
• Mortality remains high (25%; 35% in elderly) despite advances in antibiotic therapy. Morbidity is high (>30% have some neurological deficit)

Partially treated meningitis

• Patients seen early in the disease, before typical findings of meningitis appear, are sometimes diagnosed with otitis media or sinusitis and given oral antibiotics. Depending on the drug, the infection may be partially (but temporarily) suppressed
• Patients may not appear as ill and have milder meningeal signs and slower disease progression
• This situation leads to missed diagnoses

Definition

• Inflammation of meninges

Distinction between meningitis and encephalitis

• The distinction between meningitis and encephalitis is not as clear cut as it seems. Meningitis is a mainly meningeal condition (as the name would suggest) that can also affect the deeper cerebral tissue; causing some encephalitic inflammation. This may show itself as a reduced conscious level, fitting or 'cerebral irritation' (in which the patient looks a bit 'jumpy', with hyper-reflexia)
• Whereas encephalitis is an inflammation predominantly affecting the deeper cerebral tissue; but can also cause inflammation of the more superficial meninges, causing the syndrome of 'meningism' (headache, neck pain, photophobia). You can have both - ie meningo-encephalitis. Also, the same organism (eg HSV) can cause either condition, or both

Epidemiology

• Notifiable disease
  [Ref]
• Outbreaks occur (especially sub-Saharan Africa, 'Meningitis Belt')

Causes

Bacterial, acute

• Neisseria meningitidis (mainly Group B in UK),
• Streptococcus pneumoniae (commonest cause in adults)
• Haemophilus influenzae; 
• Listeria monocytogenes (poor nutritional state/alcohol)
  Note: Lyme disease, or lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia

Bacterial, chronic/subacute

• Mycobacterium tuberculosis

Viral

• 7.5% of patients with suspected meningitis; eg coxsackie, echo, mumps, polio

Fungal: eg, Cryptococcocus neoformans (HIV?)

Other

• Spirochaetal (leptospira icterohaemorrhagicae; treponema pallidum)
• Amoebic

Aseptic (rare causes)

Eythema Migrans (suggestive of Lyme Disease)

Symptoms

• The classic 'meningitic triad' (headache, neck stiffness, photophobia) is not always seen: [Ref]
• Of infection
• Leg pains, rash 
• Of shock, eg dizziness, or cold hands/feet, secondary to low BP    

Key questions

• "When did the headache start, and was it gradual (?meningitis) or sudden (?SAH)"
• "Did you vomit at the start of the headache?" (in favour of SAH)
• "Do you have migraine?"
• "Are you a 'headachey' person, and what is your normal pattern of headaches?"

Signs

• Meningism (Kernig's Sign?)
• Rash (non-blanching)
• Infection (?shock)
• Raised intracranial pressure (reduced conscious level), seizures (20%), focal neurology
  Note: look at the fundi

Typical meningococcal rash

Investigation

All patients with a fever and altered behaviour or consciousness should be investigated for CNS infection (ie do CT/LP),  unless there is clear evidence of another diagnosis

Blood

• FBC, ESR, CRP
• U+E, LFTs, Glucose (to compare to CSF glucose)
• Coagulation screen (DIC?)
• BC (50-80% positive; very important, as can have meningococcal septicaemia and no meningitis)
• ABG, if unwell
• PCR (meningococcal; 50% positive)

Other

LP (interpretation, see below);

• Normal appearance: clear, colourless
• Microbiology = gram stain; positive in 80% meningitis); cell count (normal = 0-5 white blood cells (all mononuclear), and no red blood cells); and culture/sensitivity (90% will eventually have a positive culture in meningitis)
• CSF opening pressure: normal = 10-20 cm H20
• Biochemistry = normal CSF total protein (0.1-0.4 g/L) and glucose (60-80% serum value) 
• ± PCR (meningococcal/TB?
• ± viral culture
  Note 1 (important): don't wait! If think patient may have meningitis; give AB immediately; don't wait for LP (or CT)
  Note 2: do not perform LP if predominantly septicaemic presentation (DIC), or patient is drowsy or has focal neurology - do CT first; note also that CSF may be normal if done too early. When initial CSF tests are inconclusive, repeat lumbar puncture in 8 to 24 h (or sooner if the patient deteriorates) if symptoms or signs persist. Also, remember to record the 'opening pressure' (10-20 cm H20; if low, and CSF otherwise normal, consider diagnosis of low pressure headache)

Other

• CXR: look for source of meningitis, esp lung abscess
• CT head, if reduced LoC (GCS <12), focal neurology, papilloedema, fits, bradycardia, BP
  Note: don't wait! If think patient has meningitis; give AB and do LP. If drowsy etc, do CT, then, if no sign raised ICP, consider LP
• Skull XR (source of sepsis? ie recent trauma?) Throat swab?

Key investigations

• LP, CT head

Specialist investigation

• HIV, if atypical organism, or risk factors

Differential diagnoses

Principle differential diagnoses

• SAH
• Migraine (commonest alternative diagnoses)
• Encephalitis (can have both; (why are you not 'covering your bases' and giving IV ACICLOVIR 10 mg/kg tds?)
• Cerebral vein thrombosis (can have rapid onset, CSF nearly normal, apart from sl raised protein) [Ref] [Ref]

Rarer differential diagnoses

• Abscess
• Infiltration (neoplasia, eg lymphoma)
• Other causes raised ICPMalaria
• Septicaemia (?gonococcal) ± DIC
• Tetanus

Differential diagnoses (purpuric rash and fever)

• Henoch-Schonlein Purpura
• Other vasculitides
• HUS/TTP
• Haematological malignancy
• In travellers, Rocky Mountain Spotted Fever, Viral Haemorrhagic Fevers (eg Dengue, Hanta)

LP interpretation

Note: in terms of cells, may be 'mixed' picture (polymorphs + lymphocytes); if early, or partially treated

Treatment

Find out what was given before hospital; if difficult, just give iv AB

Treatment (first line)

Drugs

• IV CEFTRIAXONE 2 g od (or CEFOTAXIME 2g qds) immediately (before LP ± CT)
• ± IV AMPICILLIN 2 g 4 hrly (>55y, to cover Listeria)
• ± IV DEXAMETHASONE 10 mg stat, then 4 mg qds for 2-4 days, prior to, or with first dose AB; only been shown to benefit patients with streptococcus pneumoniae:
  [Ref]
• ± IV ACICLOVIR 10 mg/kg tds, if encephalitis possibility
• ± antifungal?
• ± TB?
  [Ref]

Procedures

• IV (+fluids, if dry)
• OXYGEN, if hypoxic
• If unwell, urinary catheter, CVP line, arterial line

Key management decision

• CT, before LP?

Treatment (second line)

• Of shock
• ± corticosteroids, if unwell
• ?Neurosurgery (if develops abscess or hydrocephalus)
  Note: if very unwell, and not responding to ITU care, try IV CHLORAMPHENICOL 50 mg/kg (can be doubled in severe infections) qds

Precribing issues

• Don't be frightened of giving ACICLOVIR as well as AB, if you are not sure whether this is meningitis, encephalitis, both, or neither; especially if the patient is unwell, drowsy, or just does not look well

Admit?

• Always

Bed plan?

• General Medical Ward
• ± Neurology
• ± ITU

Referrals

• Microbiology
• Neurology, if atypical case, or reduced conscious level (may have hydrocephalus, or abscess, either of which may require neurosurgical intervention)

The Rest

If drowsy, focal neurology, papilloedema, or fitting do CT first; then decide on ?LP (don't let this delay AB either)

Complications

• Abscess
• Hydrocephalus
• Reduced conscious level
• Seizures (20%)
• Post-LP headache (very common)

Prognosis

• Poor prognosis, if shocked, seizures or hypotension: [Ref]  [Ref]
• Mortality: bacterial 25% (35% elderly); viral 1%
• 50% full recovery
• 25% focal neurological deficit
• 10% severe disability, or vegetative state

2° Prevention + Health Promotion

• RIFAMPICIN 600 mg bd for 2 days, in contacts of meningococcal meningitis
  Vaccines (vs meningococcus Gps A + C, if travelling to at risk areas eg students!); some neurologists recommend anti-convulsants prophylatically, if the patient has had seizures during the illness

Don't forget

• Give AB as soon as possibility of meningitis considered; then do LP (if appropriate)
• Give IV ACICLOVIR if encepahlitis possibility
• If drowsy, focal neurology, or papilloedeam or fitting, do CT first; then decide on ?LP (don't let this delay AB either)
• Ie, DON'T DO LP IF SUSPECT RAISED ICP
• Tuberculosis
• Absence of meningism, does not exclude meningitis
• Look at the fundi

Red flags

• Shock
• Rash
• Reduced conscious level 
• Focal neurological signs

References