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Pathology-Meningitis
I. Definition:
I. Definition:
- Infection of the subarachnoid space (the area between the brain and the protective membranes).
- Viral Meningitis: Approximately 11 cases per 100,000 people per year.
- Bacterial Meningitis: Approximately 3 cases per 100,000 people per year. Note the significantly lower incidence compared to viral meningitis.
- Viral Meningitis: Most commonly caused by echoviruses and coxsackieviruses. No organism is cultured from CSF.
- Bacterial Meningitis:
- Most common causes: Neisseria meningitidis (meningococcus) and Streptococcus pneumoniae (pneumococcus).
- Neonates (newborns): Escherichia coli and Group B streptococci are significant causes.
- CSF culture and/or blood cultures will yield the causative organism.
- Bacterial Meningitis: Bacteria typically enter the bloodstream from the nasal cavity (often following a viral upper respiratory infection). Their capsules provide resistance to phagocytosis (immune cell engulfment) and complement (part of the immune system). Bacteria exploit weaknesses in the blood-brain barrier (e.g., the choroid plexus) to access the subarachnoid space. Rapid bacterial multiplication in the cerebrospinal fluid (CSF) triggers an acute inflammatory response within the meninges.
- Viral Meningitis: The pathogenic mechanisms are less detailed in the provided text, but it implies a similar entry point via the bloodstream but without the bacterial capsule-related resistance to immune response.
- Common Symptoms (both viral and bacterial): Headache, fever, neck stiffness (meningismus), photophobia (light sensitivity).
- Severity: Bacterial meningitis typically presents with more severe symptoms than viral meningitis.
- Lumbar Puncture (Spinal Tap): CSF analysis is crucial.
- Viral Meningitis: CSF will show a predominance of lymphocytes (a type of white blood cell).
- Bacterial Meningitis: CSF will show a predominance of neutrophils (another type of white blood cell).
- Gram Staining (Bacterial Meningitis): Helps identify the bacteria present in the CSF, aiding in rapid diagnosis and treatment.
- Culture (Bacterial Meningitis): CSF and/or blood cultures are used to grow and identify the specific bacteria.
- Viral Meningitis: Generally mild, with complete recovery expected.
- Bacterial Meningitis: Much more serious; potentially life-threatening if not treated promptly with appropriate antibiotics. Severe cases can lead to permanent neurological complications including hearing loss, learning disabilities, paralysis, and epilepsy.
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