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Introduction. Encephalitis is an acute inflammatory process affecting the brain Viral infection is the most common and important cause, with over 100 viruses implicated worldwide Symptoms Fever Headache Behavioral changes Altered level of consciousness Focal neurologic deficits Seizures

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Introduction

Introduction

  • Encephalitis is an acute inflammatory process affecting the brain

  • Viral infection is the most common and important cause, with over 100 viruses implicated worldwide

  • Symptoms

    • Fever

    • Headache

    • Behavioral changes

    • Altered level of consciousness

    • Focal neurologic deficits

    • Seizures

  • Incidence of 3.5-7.4 per 100,000 persons per year


Herpes simplex encephalitis

Herpes Simplex Encephalitis

  • Commonest and gravest form of sporadic acute encephalitis.

  • Between 30 and 70 percent are fatal, and the majority of patients who survive are left with serious neurologic abnormalities.

  • Sporadically throughout the year and in patients of all ages and in all parts of the world.

  • Almost always to HSV-1, which is also the cause of the common herpetic lesions of the oral mucosa.

  • The type 2 virus may also cause acute generalized encephalitis, usually in the neonate and in relation to genital herpetic infection in the mother.


Pathology

Pathology

  • With reactivation in the trigeminal ganglia, the infection may spread along nerve fibers that innervate the leptomeninges of the anterior and middle fossae.

  • Both direct virus-mediated and indirect immune-mediated mechanisms play a role in producing CNS damage

  • Intense hemorrhagic necrosis of the inferior and medial temporal lobes and the medioorbital parts of the frontal lobes

  • Temporal lobe lesions are usually bilateral but not symmetrical

  • Intranucleareosinophilic inclusions are found in neurons and glial cells.


Clinical features

Clinical Features

  • Over several days

  • Fever, headache, seizures, confusion, stupor, and coma.

  • Findings that betray the predilection of this disease for the inferomedial portions of the frontal and temporal lobes.

  • Olfactory or gustatory hallucinations, anosmia, temporal lobe seizures, personality change, bizarre or psychotic behavior or delirium, aphasia, and hemiparesis.

  • Swelling and herniation of one or both temporal lobes through the tentorium may occur

  • Status epilepticus is rare.


Herpes simplex encephalitis1

Herpes Simplex Encephalitis

  • The CSF is typically under increased pressure

  • Almost invariably shows a pleocytosis (range, 10 to 200 cells per cubic millimeter, infrequently more than 500).

  • The cells are mostly lymphocytes,

  • In a few cases, 3 to 5 percent in some large series, the spinal fluid has been normal in the first days of the illness.

  • In only a minority of cases, red cells, sometimes numbering in the thousands, and xanthochromia are found

  • The protein content is increased in most cases.

  • Rarely, the CSF glucose levels may be reduced to slightly less than 40 mg/dL, creating confusion with tuberculous and fungal meningitides


Diagnosis

Diagnosis

  • CT scans show hypodensity of the affected areas in 50 to 60 percent of cases

  • MRI shows signal changes in almost all (increased signal in T2-weighted images).

  • T1-weighted images demonstrate areas of low signal intensity with surrounding edema and sometimes with scattered areas of hemorrhage occupying the inferior parts of the frontal and temporal lobes.

  • Almost always the lesions enhance with contrast


Diagnosis1

Diagnosis

  • Detection of HSV antigen in the CSF by the application of PCR

  • The test has extremely high sensitivity (98 percent) and specificity (94 to 100 percent)

  • Antiviral treatment did not appear to affect the test.

  • False-negative tests are most likely to occur in the first 48 h of febrile infection.

  • Fluorescent antibody study and by viral culture of cerebral tissue obtained by brain biopsy


Treatment

Treatment

  • Acyclovir significantly reduces both mortality and morbidity from the disease

  • Initiate treatment while confirmatory testing is being carried out.

  • Early treatment

  • Before loss of consciousness

  • Within 24 hours of the onset of symptoms

  • Glasgow Coma Scale score of 9 to 15

  • The duration of treatment of HSV encephalitis in immunocompetent patients should be 14 to 21 days


Herpes simplex encephalitis2

Herpes Simplex Encephalitis

  • Antiviral therapy may be discontinued if a negative CSF HSV PCR result is obtained after 72 hours following onset of neurological signs and symptoms.

  • Clinicians must consider alternative reasons for a false-negative CSF PCR result, including early testing after the onset of symptoms, or presence of PCR inhibitors (eg, hemoglobin degradation products in bloody CSF)


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