Central nervous system infections: Pathology review

Summary

This script discusses central nervous system (CNS) infections, including meningitis, encephalitis, and brain abscesses, focusing on their causes, clinical presentation, diagnostic methods, and treatment approaches. The script highlights various pathogens such as bacteria, viruses, fungi, and parasites, and the differential diagnosis based on clinical signs and cerebrospinal fluid analysis. It reviews three patient cases, detailing how their symptoms point toward specific diagnoses, such as bacterial meningitis, viral encephalitis, and brain abscess. The importance of timely diagnosis through lumbar puncture, imaging, and empirical treatment is emphasized for improving patient outcomes.

Takeaways

• 😀 Meningitis, encephalitis, and brain abscesses are major types of central nervous system (CNS) infections with distinct clinical presentations and causes.
• 😀 Meningitis can be caused by a variety of pathogens, including bacteria (e.g., Streptococcus pneumoniae), viruses (e.g., enteroviruses), fungi (e.g., Cryptococcus), and parasites (e.g., Naegleria fowleri).
• 😀 Acute bacterial meningitis is more life-threatening than viral meningitis, with causative organisms varying by age, such as Group B Streptococcus in infants and Neisseria meningitidis in adolescents.
• 😀 Viral encephalitis is often caused by herpes simplex virus (HSV), which primarily affects the temporal lobe and can be reactivated under conditions of immune suppression.
• 😀 Brain abscesses usually develop from local infections like otitis media or mastoiditis, or from hematogenous spread, and are characterized by ring-enhancing lesions on imaging.
• 😀 Key diagnostic tools for CNS infections include lumbar puncture (LP) to analyze cerebrospinal fluid (CSF), CT or MRI for imaging, and specific PCR tests for viruses like HSV.
• 😀 A lumbar puncture is contraindicated in patients with suspected brain abscesses due to the risk of cerebral herniation from increased intracranial pressure (ICP).
• 😀 Empiric treatment for CNS infections typically starts with broad-spectrum antibiotics and, in suspected HSV encephalitis, intravenous acyclovir before PCR results confirm the diagnosis.
• 😀 In patients with suspected meningitis or encephalitis, the CSF analysis shows increased white blood cell count, elevated protein, and decreased glucose levels in bacterial infections, while viral infections often show normal or slightly decreased glucose levels.
• 😀 For HIV-positive individuals with CNS infections, the differential diagnosis includes toxoplasmosis (treated empirically with pyrimethamine and sulfadiazine) and primary CNS lymphoma (which may require biopsy for confirmation).

Q & A

What are the key clinical signs that suggest Mike is likely suffering from meningitis?

Mike's key clinical signs include fever, headache, photophobia, neck stiffness, and positive Kier and Brinsky signs. These meningeal signs strongly suggest meningitis as the diagnosis.

What is the significance of lumbar puncture findings in Mike's case?

Mike's lumbar puncture reveals a predominantly neutrophilic pleocytosis, elevated protein, and low glucose, which are classic findings of bacterial meningitis. These findings guide the need for immediate empiric antibiotic therapy.

Why are Kier and Brinsky signs useful in diagnosing meningitis, and how are they performed?

Kier and Brinsky signs help detect meningeal irritation, a hallmark of meningitis. To perform the Kier sign, the patient’s hip is flexed to 90 degrees, and the knee is extended. Pain with extension is positive. The Brinsky sign involves passive neck flexion, causing involuntary hip flexion if positive.

How does Helen’s presentation suggest viral encephalitis rather than meningitis?

Helen's presentation of fever, headache, and confusion, without meningeal signs (e.g., neck stiffness), along with patchy temporal lobe enhancement on head CT, suggests viral encephalitis, specifically HSV encephalitis.

Why should empiric acyclovir be started for Helen, even before confirming the diagnosis of HSV encephalitis?

Empiric acyclovir is started for Helen due to the suspicion of HSV encephalitis, especially with temporal lobe enhancement on CT. Early treatment is crucial to reduce the risk of permanent neurological damage while awaiting PCR confirmation.

What diagnostic test would confirm HSV as the causative agent in Helen's case?

A PCR test of the cerebrospinal fluid (CSF) would confirm HSV as the causative agent of Helen's viral encephalitis.

Why is a lumbar puncture contraindicated in Lucia's case?

In Lucia’s case, lumbar puncture is contraindicated because of the high likelihood of increased intracranial pressure (ICP), which could lead to cerebral herniation. This risk is assessed through clinical signs like papilledema.

What findings on CT scan support the diagnosis of a brain abscess in Lucia?

Lucia's CT scan reveals a single ring-enhanced lesion, which is characteristic of a brain abscess. Additionally, her recent history of otitis media is a clue to the source of the abscess.

What is the main distinction between meningitis and encephalitis, and how does it relate to diagnosis?

Meningitis typically involves inflammation of the meninges, with symptoms like fever, headache, and neck rigidity. Encephalitis, however, involves brain tissue inflammation, leading to altered mental status, confusion, and personality changes. This distinction helps guide treatment.

What are the general diagnostic steps for CNS infections, and how do they differ for brain abscesses?

For most CNS infections, the diagnostic steps include clinical evaluation, lumbar puncture for CSF analysis, and imaging (CT or MRI). However, in cases of brain abscesses, a lumbar puncture is contraindicated, and imaging (especially CT or MRI) is critical to identify ring-enhancing lesions, which suggest an abscess.