Meningitis: Etiology, Types, Pathogenesis, Differentiating Factors, and CSF Findings

Etiology of Meningitis

Meningitis is an inflammation of the meninges, primarily caused by infections. The major etiological classifications include:

• Bacterial Meningitis: Common pathogens include Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae.
• Viral Meningitis: Frequently caused by enteroviruses, herpes simplex virus, and arboviruses.
• Fungal Meningitis: Cryptococcus neoformans is a leading fungal cause, often affecting immunocompromised individuals.
• Parasitic Meningitis: Rare, but may result from parasites such as Naegleria fowleri.

Types of Meningitis

Meningitis can be classified based on its causative agent:

• Acute Meningitis: Rapid onset of symptoms, usually caused by bacteria or viruses.
• Chronic Meningitis: Develops over weeks or months, often due to fungi or tuberculosis.
• Aseptic Meningitis: Typically viral or non-infectious in origin.

Pathogenesis

The pathogenesis of meningitis involves microbial invasion, inflammation, and subsequent immune response:

• Pathogens breach the blood-brain barrier.
• Inflammatory cytokines trigger immune response.
• Edema and increased intracranial pressure lead to neurological symptoms.

Differentiating Factors

Key clinical differentiators among different types:

• Bacterial Meningitis: High fever, neck stiffness, altered mental status.
• Viral Meningitis: Milder symptoms, often self-limiting.
• Fungal Meningitis: Gradual onset, often seen in immunocompromised individuals.

CSF Findings in Meningitis

Type	Appearance	Cell Count	Glucose	Protein
Bacterial	Turbid	Elevated neutrophils	Low	High
Viral	Clear	Elevated lymphocytes	Normal	Moderate
Fungal	Cloudy	Elevated lymphocytes	Low	High