Neurological Infections

Meningitis

This is inflammation of the leptomeninges (pia and arachnoid mater) lining the brain.

It is most commonly due to an infectious agent, which can lead to an increase in intracerebral pressure and the development of cerebral oedema.

If left untreated, it can lead to hydrocephalus, hearing loss, fibrosis and death by cerebral herniation.

Causes

Viruses (most common cause), e.g., enterovirus (coxsackie, echovirus), mumps, herpesviruses, measles

Bacterial causes are less common but more serious

In adults, the most common bacteria is N. meningitidis and S. pneumoniae

In babies, group B streptococci and E. coli are common causes

Symptoms

Early – headache, fever, photophobia, nuchal rigidity

Late – altered mental status with low GCS, seizures

Non-blanching maculopapular rash with N. meningitidis infection

Key tests

Blood tests show raised inflammatory markers (WCC, CRP)

Lumbar puncture – analysed for cell microscopy and culture, protein, and glucose

If bacterial – high neutrophils, low CSF glucose, usually raised protein

If viral – increased lymphocytes, normal CSF glucose, low protein

If fungal (atypical) – increased lymphocytes, decreased CSF glucose, high protein 

Management

If in GP setting and suspected meningococcal bacteria, give IM benzylpenicillin and send to hospital

If in hospital, take blood cultures first and ideally perform an LP prior to empirical antibiotics and antivirals, unless the LP is contra-indicated

Viral meningitis does not usually require treatment

If bacterial, the mainstay of treatment is empirical antibiotics according to local trust guidelines. An example is below:

If 3 months–50 years, IV ceftriaxone

If < 50 years, IV cefotaxime and amoxicillin

If penicillin allergic, can give chloramphenicol

IV dexamethasone may also be given, especially in pneumococcal meningitis

Encephalitis

This is inflammation of the brain parenchyma. It can occur due to both infectious and autoimmune causes but is most commonly due to is Herpes simplex virus (HSV-1).

It has similar symptoms to meningitis, but also classically affects the temporal and inferior frontal lobes causing focal neurological symptoms.

Symptoms

Meningitis-like symptoms – fever, headache, vomiting, confusion

Neurological features – aphasia (due to speech centers in the temporal lobe), psychiatric symptoms, seizures

Key tests

Lumbar puncture – CSF shows a viral picture (if due to HSV-1)

CSF analysis using PCR shows viral DNA (diagnostic test)

EEG shows lateralised periodic discharges at 2 Hz

MRI – high T2 signal in affected lobes. Can also cause intracerebral haemorrhage

Management

If viral encephalitis, give IV acyclovir

Poliomyelitis

A condition which is spread by the polio virus faeco-orally in contaminated water.

After entering the gut, it can invade the nervous system, causing aseptic meningitis as well as destroying motor neurones leading to irreversible paralysis.

Symptoms

Flu-like prodrome – fever, headache, vomiting, tremor

Leads to LMN symptoms (weakness, paralysis, fatigue)

Can also cause meningitis

Key tests

Detection in stool sample

Management

No cure available. The disease can be prevented by the polio vaccine, with multiple doses required for lifelong protection.

Botulism

This is a condition due to a neurotoxin made by the bacterium Clostridium botulinum.

This is acquired either by contracting the bacteria in wounds or from acquiring the toxin directly from contaminated foods.

The toxin cleaves SNAP proteins, which prevents exocytosis of acetylcholine at the neuromuscular junction causing flaccid paralysis. 

Symptoms

Flaccid paralysis, diplopia, ptosis

Can lead to respiratory failure

Autonomic signs – dry mouth, urinary/ cardiac/GI dysfunction

Lack of sensory changes

Management

Botulinum antitoxin, may require ITU for respiratory support

Rabies

A condition which is caused by the lyssavirus, which causes an acute encephalitis with the development of Negri cytoplasmic inclusion bodies in CNS neurones.

It is transmitted in the saliva of infected mammals (dog, bat, fox).

Whilst there is no cure, patients can be vaccinated against rabies.

Symptoms

Flu-like prodrome (headache, fever, general malaise)

Furious rabies – this is characterised by encephalitis causing hydrophobia, water triggering muscle spasms, hypersalivation and hyperactivity

Paralytic rabies – muscle weakness, loss of sensation and paralysis in bitten limb

If left untreated, may progress to coma and death

Key tests

Viral PCR/fluorescent antibody test

Management

Before symptoms have developed, multiple-dose immunisation protocol

If the patient has been immunised, 2 further doses of the vaccine should be given

If not previously immunised, the patient requires vaccination and human rabies immunoglobulin (HRIG)