Diagnosis

Encephalitis

Etiology

Cause [6yb][nqf]

1. Virus: HSV (reactivation), VZV, EBV, CMV (immune-compromised state), HHV6, measles virus, mumps virus, rubella virus, St Louis encephalitis, West Nile encephalitis, California Encephalitis, Venezuelan Equine Encephalitis, Eastern Equine Encephalitis, Western Equine Encephalitis, Japanese Encephalitis

   Usually the virus gains entry to the CNS either by hematogenous spread or by travel along neural pathways (rabies virus, HSV, VZV).

2. Bacteria: Toxoplasma gondii, syphilis, Mycoplasma species and those causing rickettsial disease or catscratch disease.

3. Other infections: Parasitic, Amoebic, Fungal

4. Autoimmune: inflammation due to autoimmunity towards proteins in the brain

   • Acute disseminated encephalomyelitis (ADEM)

   • Anti-NMDA receptor encephalitis

   • Hashimoto’s encephalopathy

   • LGI1/CASPR2-antibody encephalitis

   • Limbic encephalitis

   • Rasmussen’s encephalitis

5. Cancer

6. Medicines

Pathophysiology [6yb]

1. Infection: [nqf]

   • Person-to-person contact

   • Animal vectors: mosquitoes, ticks (arbovirus) and mammals (rabies, lymphocytic choriomeningitis)

   • Hematogenous spread to the spinal cord

   • Retrograde travel to the CNS from nerve endings: HSV, rabies, HZV

   • Host’s inflammatory response disrupt neural cell function

   • Cerebral edema, vascular congestion, hemorrhage and neuronal necrosis

2. Autoimmune: [4ig]

   • Loss of immune tolerance of unknown cause

   • Autoimmune antibodies target synaptic proteins --> widespread inflammation

Complications [nqf]

• Cognitive impairment

• Mood and behavior changes

• Residual neurological deficits

• Extrapyramidal symptoms

• Hyponatremia

• Encephalopathy

• Mononeuropathy

• Flaccid paralysis

• SIADH

Epidemiology

Incidence per 100.000 [nqf][4ig][idy][fq5][9yy]

Approach

• Blood test: antibodies [6yb][4ig]

• Glucose

• Blood culture

• Toxicology

• Lumbar puncture: pressure, viral/bacterial culture, viral PCR, CSF cell count, pH, lactate, protein, and glucose

• CT caput

• MR caput

• EEG

• Brain biopsy

Treatment

1. Supportive care: oxygen, fluid, painkiller, anticonvulsant, antipyretic, anxiolytic [6yb]

2. Viral encephalitis:

   • Acyclovir 10 mg/kg q8h for 14-21 days (with or without antibiotics or steroids)

3. Autoimmune encephalitis: pathogenic antibody depletion

   • Immunotherapy (steroids, intravenous antibodies or plasma exchange)

4. Increased intracranial pressure and hydrocephalus:

   • Elevate the head

   • Monitoring neurologic status

   • Diuretic (eg, furosemide 20 mg IV, mannitol 1 g/kg IV)

   • Dexamethasone 10 mg IV q6h reduce edema

   • Hyperventilation (arterial CO2 tension [PaCO2] 30 mm Hg) to control increasing ICP on an emergency basis

   • Intraventricular ICP monitoring is controversial

5. Surgery if encephalitis was triggered by a tumor

Differential diagnoses

Brain abscess, Brain tumor, Cat scratch disease, Delirium tremens, Ehrlichiosis, Epilepsy, Febrile seizure, Hypoglycemia, Intoxication, Intracerebral hemorrhage, Leptospirosis, Lyme disease, Meningitis, Multiple sclerosis, Psychosis, Rocky mountain spotted fever, Stroke, Subarachnoid hemorrhage, Subdural empyema, Syndrome of inappropriate antidiuretic hormone secretion, Syphilis, Systemic lupus erythematosus, Toxoplasmosis, Tuberculosis