12A. Encephalitis

Encephalitis

Encephalitis refers to inflammation of the brain, which causes CNS damage and damage to the blood-brain barrier. It is usually viral or immune-mediated. It often co-exists with meningitis as meningoencephalitis.

Etiology

• Viral
  • HSV – topic 19B
  • HZV – topic 19B
  • Tick-borne encephalitis (TBE)
  • Poliomyelitis
  • Rabies
• Immune-mediated
  • Postvaccination and parainfectious encephalomyelitis
  • Autoimmune-limbic encephalitis
  • Paraneoplastic encephalitis – topic 24A
• Bacterial (rare)

Classification

We can also classify types of encephalitis according to the part of the brain which is affected:

• Polioencephalitis – grey matter affected
  • HSV encephalitis
  • Tick-borne encephalitis
  • Poliomyelitis
  • Rabies
• Leukoencephalitis – white matter affected
  • Postvaccination and parainfectious encephalomyelitis
  • Progressive multifocal leukoencephalopathy (PML)
• Panencephalitis – grey and white matter affected
  • Subacute sclerotizing panencephalitis
  • Rubeola panencephalitis

Clinical features

The clinical features of all types of encephalitis are similar. The patient may have:

• Flu-like symptoms
• Meningeal signs
• Focal neurological deficits
• Epileptic seizures
• Altered mental status
• Behavioural changes

Altered mental status, seizures, and focal neurological deficits are very suspicious for encephalitis.

Diagnosis and evaluation

Lumbar puncture is the most important evaluation. The CSF will have oligoclonal bands, lymphocytes, and high protein levels. MRI is also important, on which focal or multifocal lesions and oedema are present. PCR of the CSF can give the viral etiology, if present. In case of seizures, EEG is important.

Many immune-mediated encaphalitides are characterised by the presence of autoantibodies in the CSF and serum. Cancer evaluation is important as many cases are paraneoplastic.

Treatment

The treatment depends on the cause. HSV should be treated with acyclovir, and immune-mediated types should be treated with immunotherapy, usually steroids/IVIG.

Special types of encephalitis not covered in other topics

Rasmussen encephalitis

Rasmussen encephalitis is a very rare (0,2 per million) autoimmune cause of encephalitis with specific clinical features. Interestingly, the autoimmune process affects only one hemisphere. It affects children and causes unilateral cerebral atrophy which causes progressive hemiparesis and focal seizures. These seizures often progress into focal motor status epilepticus, called epilepsia partialis continua. The best treatment is hemispherectomy of the affected hemisphere. Immunotherapy is not usually efficacious.

This disease is important according to prof. Pfund.

Subacute sclerotising panencephalitis

Subacute sclerotising panencephalitis (SSPE) is a complication of measles infection. It develops several years (>7) after the initial measles infection, and affects both gray and white matter. The infection causes dementia, myoclonus, epilepsy, invariably leading to death within a few years. There is no treatment, but the vaccine prevents the initial infection and therefore this complication.