CNS Infections - Viral Encephalitis and Bacterial Meningitis - Differential Diagnosis Framework



Viral Encephalitis:

MCC: Enteroviruses (e.g., coxsackievirus or Echovirus).



Herpesviruses (MCC: HSV 1):

 • Herpes simplex virus 1 and 2

 • Varicella-zoster virus

 • CMV

 • EBV

 • HHV6

Others:

 • Adenovirus,

 • Lymphocytic choriomeningitis virus (LCMV), influenza, parainfluenza, and mumps.

 • Arboviruses:

	- West Nile virus (WNV), Zika, chikungunya, dengue, LaCrosse, Saint Louise encephalitis, eastern equine encephalitis virus,

	- Jamestown Canyon virus, Snowshoe Hare virus

	- Powassan, louping ill virus and Coltivirus



Symptoms:

 • Headache

 • Fever

 • Nuchal rigidity

 • Photophobia

 • Nausea, vomiting

 • Myalgia, pharyngitis

 • Maculopapular rash

 • Cough

 • Changes in alertness, confusion, or hallucinations



CSF Analysis:

 • Lymphocytic pleocytosis

 • A mildly elevated protein level (< 1g/L)

 • Mildly decreased/Normal glucose level,

 • Normal opening pressure



Lyme Meningoencephalitis:

 • 2 to 10 weeks after erythema migrans develops.

 • Common clinical features include

	- Headache, photophobia, nausea,

	- History of erythema migrans,

	- Tick bite in an endemic area,

	- Facial paralysis, which can be unilateral or bilateral.



Treponema Pallidum Meningitis:

 • Headache and meningismus are common

 • CSF usually shows a lymphocytic pleocytosis with an elevated protein level.

 • In tertiary syphilis, neurosyphilis can be asymptomatic or symptomatic.

 • Symptomatic neurosyphilis can present with primarily meningovascular (stroke presentation) or parenchymatous (tabes dorsalis, general paresis) features



Bacterial Meningitis:

MCC:

 • Streptococcus pneumoniae,

 • Neisseria meningitidis (40%)

 • Listeria monocytogenes

 • Haemophilus influenzae



Symptoms:

 • Acute meningeal signs (fever, nuchal rigidity)

 • Altered mental status.



CSF Analysis:

 • Neutrophilic predominance

 • Protein level 100-500 mg/dL

 • Glucose level: <40 mg/dL

 • Normal opening pressure

 • Gram stain: Positive in 60%-90%

 • Culture: Positive in 70%-85%

 • Negative CSF Gram stain: Previous antibiotics, L. Monocytogenes or gram negative bacilli (< 50%)

 • S. pneumoniae antigen detection in the CSF has a 99% sensitivity and specificity



Leptospiral Meningitis - Develops in the immune or second phase of the illness:

 • Uveitis

 • Rash

 • Conjunctival suffusion

 • Lymphadenopathy

 • Hepatosplenomegaly

 • The CSF formula resembles enteroviral meningitis, and the diagnosis is established by CSF or urine culture or by serology.



CSF Lactate:

Good indicator to differentiate bacterial from viral meningitis

 • In Bacterial meningitis

 • CSF-lactate ≥ 4.2 mmol/l is regarded as a strong indicator of a non-viral meningitis with a diagnostic sensitivity and specificity of up to 93-99% and 88-94%.



by Dr. Kushal Vaishnani @k_vaishnani and Ravi Singh @rav7ks



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