BY
Dr Nansel, Charles

 

OUTLINES

  • Definition
  • Epidemiology
  • Etiology
  • Pathology
  • Clinical features & Diagnosis
  • Treatment
  • Prognosis
  • Complications
  • Differentials

 

DEFINITION

  • Encephalitis is an acute inflammatory process affecting the brain parenchyma tissue clinically expressed by fever, impaired consciousness, seizures, focal neurologic deficits.

Variants

  • Encephalomyelitis — affecting the spinal cords
  • Encephalomyeloradiculitis —- affecting the nerve roots
  • Meningoencephalitis —– affecting both the meninges and brain parenchyma

 

EPIDEMIOLOGY

  • In the united states, <20,000 cases reported annually
  • Incidence of 3.5-7.4 per 100,000 persons per year

RISK FACTORS

  • Age –young and older adults are at greater risk
  • Weakened immune system– HIV/AIDS patients on immune suppressing drugs
  • Geographical regions—mosquito or tick borne viruses are common in particular geographical regions

 

AETIOLOGY (Causes)

  • Viral infection is the most common and important cause, with over 100 viruses implicated worldwide
  • Herpes viruses –HSV-1, HSV-2, Varicella zoster virus (VZV), Cytomegalovirus (CMV), Epstein-Barr virus (EBV), Human herpes virus 6
  • Adenoviruses
  • Enteroviruses, e.g. Poliovirus, Coxsackie virus
  • Measles, Mumps and Rubella viruses
  • Arboviruses – examples; Japanese encephalitis, St loius encephalitis virus; West Nile encephalitis virus;Eastern, Western and Venezulean equine encephalitis; tick borne encephalitis virus
  • Bunyaviruses—examples; La Crosse strain of californis virus
  • Renoviruses—example; Colorado tick fever virus
  • Arenaviruses—-example; lymphocytic choriomeningitis virus

NON-VIRAL CAUSES

Not all cases of encephalitis are caused by viruses

Some other causes include:

  • BACTERIA
  • FUNGI
  • PARASITES
  • NON INFECTIOUS CAUSES e.g. allergic reaction, toxins.

 

PATHOLOGY

Viral encephalitis is characterised by the following

  • Diffuse damage to the cell in the cortex, basal ganglia and brain stem
  • Inclusion bodies are present in the neurons and the glial cells
  • Infiltration of the brain substance by inflammatory cells (polymorphs initially, followed later by lymphocytes and monocytes)
  • These cells are found between the neurons and in the perivascular spaces
  • Neuroglia proliferation is also seen
  • The herpes simplex virus often infects the temporal lobes while the substantia nigra, mid brain and basal ganglia are usually involved in encephalitis lethargica

 

HERPES SIMPLEX VIRUS (HSV)

  • Two types have been identified (HSV-1&2)
  • HSV-1 major cause of herpetic stomatitis, herpes labialis, keratoconjuctivitis and encephalitis
  • HSV-2 -causes genital herpes

HSV-1

  • Portal of entry is usually through the mouth, occasionally skin.
  • Primary infection may go unnoticed or may produce a severe inflammatory reaction with vesicle formation leading to painful ulcers
  • Virus remain latent in trigeminal ganglia but may be reactivated by stress, trauma, febrile illness producing cold sore.

HSV-2

  • Affects the genitals
  • Remains latent in the sacral ganglia
  • Gives pain in the groin, buttock and upper thigh (radiculomyelopathy)
  • Neonates may develop primary HSV infection following vagina delivery in the presence of active genital HSV infection in the mother.
  • Immunocompromised patients e.g. those receiving intensive cancer chemotherapy may develop disseminated HSV infection involving the viscera.

CLINICAL MANIFESTATION

  • Flu-like symptoms (fever, sore throat, cough and malaise)
  • If meningitis and encephalitis, (headache, stiff neck, vomiting)
  • Infants may have bulging in the fontanelles or soft spot on the skull
  • Altered level of consciousness (confusion, behavioural abnormalities)
  • Mild lethargy to coma, focal neurological deficit
  • Focal or generalized seizure
  • Hallucination
  • Agitation
  • Personality change
  • Behavioural disorders
  • Tremors
  • CN deficits e.g. ocular palsies, facial weakness
  • Temperature dysregulation

DIAGNOSIS

  • Blood culture
  • Lumbar puncture – (lymphocytic pleocytosis >5cells
  • Normal glucose concentration
  • CSF culture
  • CSF PCR
  • Brain imaging— (MRI or CT) shows edema
  • EEG shows slow wave change

DIFFERENTIALS

  • Bacterial meningitis with cerebral edema
  • Brain abscess
  • Cerebral malaria
  • Cerebral venous thrombosis

TREATMENT

  • No specific medications to treat it
  • Acyclovir (Zovirax)— (10mg/kg) 3times daily for 2-3weeks
  • Ganciclovir (caused by cmv n hsv1)
  • Anti-convulsant to prevent and treat seizures
  • Corticosteroids may be given to reduce brain inflammation
  • Sedatives can be effective for seizures, restlessness
  • analgesics
  • Nutritional and dietary supplements
  • Eat antioxidant foods including fruits e.g. Cherries, tomatoes, vegetables
  • Avoid caffeine, alcohol and tobacco

Supplements

  • Vitamin C (500-1,000mg 1-3daily) as an anti-oxidant, and to boost immune system
  • Probiotic supplement for digestive and immune system health.
  • Omega-3-fatty acids such as fish oil (1-3times daily) to help decrease inflammation and boost immune system.

PROGNOSIS:

  • The prognosis is dependent on the virulence of the virus and the patient’s health status.
  • Extremes of age(<1y or >55y), immune-compromised status, and preexisting neurologic conditions are associated with poorer outcomes.

COMPLICATIONS

  • Keratitis
  • Skin infections such as herpetic whitlow and erythema multiforme
  • Dendritic ulceration
  • Epilepsy
  • Memory loss
  • Aphasia

PREVENTION   

  • Vaccination– vaccines which include measles, mumps, rubella.
  • Avoid mosquito infested areas

 

 

 

REFERENCES

  • Kumar & Clark: Clinical medicine, 17th edition
  • Harrison’s Textbook of Medicine, 11th edition
  • A compendium of Clinical Medicine, by O.O Akinkugbe.