Viral CNS Infections

Viral CNS Infections

Viral Encephalitis

·        Herpes Simplex: 

o  Clinical: usually short history, fever, headache, confusion, ataxia, focal convulsions ® coma (if clouding of consciousness consider encephalitis in addition to meningitis) 

o  CSF: raised leucocyte count, predominantly mononuclear

o  Diagnosis: PCR test of CSF for Herpes Simplex antigen

o  Treatment: Acyclovir 10 mg/kg iv 8 hourly for 10 days.  Low threshold for treatment

·        HIV:

o  Most AIDS patients have a subacute encephalitis caused by direct brain infection

o  Symptoms: mood changes, depression, lethargy, confusion, dementia

·        Other viruses: Mosquito born (Murray Valley Encephalitis, Japanese Encephalitis), Rabies virus

·        Management: 

o  Full blood screen: Cr, electrolytes, glucose, LFT, ABG, urine drug & metabolic screen, blood and urine cultures, ammonia, cortisol, coagulation screen, ECG

o  Serology and viral cultures

o  LP if not contraindicated – may be normal in up to 50% of cases

o  Consider empiric acyclovir + cefotaxime – at least until HSV is excluded

o  CT (MRI better still) for focal lesions

·        Consider differential:

o  Head injury

o  Toxic or metabolic encephalopathy

o  Hypoxic insult

·        Supportive treatment:

o  Fluid restriction

o  Control of seizures

o  Cardio-respiratory support

o  Maintenance of nutrition

Viral Meningitis

·        Causes:

o  Most due to non-polio enteroviruses:

§  Faecal ® oral Þ little kids at risk

§  ECHO viruses, Polio, Coxsackie A & B

o  Mumps 

·        Presentation: fever, headache, malaise, photophobia, abdominal pain and vomiting. Neck stiffness in older children. Maybe a macular or even petechial rash

·        Differential diagnosis of lymphocytic (aseptic) meningitis

o  Viral meningitis (eg ECHO, Mumps, Coxsackie)

o  Viral Encephalitis (eg Herpes Simplex, CMV, Varicella Zoster)

o  TB meningitis

o  Fungal meningitis (eg Cryptococcus neoformans)

o  Neurosyphilis

o  Acute Leptospirosis

o  Cerebral toxoplasmosis

o  Neoplasm

o  Cerebral sarcoid

·        Lab tests:

o  CSF Culture: Enteroviruses, mumps, fungi, TB

o  Throat culture and Faeces for enteroviruses

o  CSF Antigen tests: PCR for Herpes Simplex, CMV, VZV, TB, Toxoplasmosis

o  Serology: antibodies to Treponema pallidum, Leptospira, Toxoplasma gondii

·        Admit if:

o  Diagnosis in doubt

o  Antibiotics are being considered

o  IV Rehydration is needed

·        Ensure good analgesia

Post-Infective Encephalitis

·        Immune hypersensitivity reaction to host cells containing viral antigens

·        Late onset – 7 – 10 days after acute illness

·        Viruses involved: Morbilli (Measles), Mumps, Rubella, Varicella-Zoster

Other

·        Spongiform encephalopathies:

o   Caused by Prions (Proteinaceous infectious particles)

o   Histology: vacuolation of brain tissue, deposition of amyloid plaques

o   Eg: Kuru (in PNG), Creutzfeldt-Jakob Disease (CJD), Variant CJD

o   Symptoms: Insidious onset of ataxia, dysarthria and dysphagia.  Progressive dementia

·        Slow virus infections:

o   SSPE (Subacute sclerosing pan-encephalitis): Measles like virus affecting children and adolescents 

o   PML (Progressive Multifocal Leucoencephalopathy): Affects adults from 40 – 70, Polyoma virus implicated.

·        Neonatal Encephalitis:

o   TORCH Complex: Toxoplasmosis, Rubella, CMV, Herpes Simplex

o   Usually accompanied by disseminated disease

·        Reye‟s Syndrome: post-infectious encephalopathy with associated acute liver failure. Most common antecedent infection is Influenza virus