Meningitis and brain abscess: Clinical sciences

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Introduction0:00–0:39

Meningitis refers to inflammation of the meninges, the protective membranes covering the brain and spinal cord, most often due to an infection.
On the flip side, brain abscess refers to an encapsulated area of purulent infection within the brain parenchyma. The underlying mechanism for both types of infections include contact with a specific pathogen via direct inoculation, such as from penetrating trauma; contiguous spread, for example, from the facial sinuses; or hematogenous spread of pathogens from distant focal infections.
Now, if a patient presents with a chief concern suggestive of meningitis or brain abscess, perform an ABCDE assessment to determine if they are stable or unstable.

Unstable Patient0:39–1:23

If unstable, stabilize the airway, breathing, and circulation. At this point, you might even have to intubate the patient and start mechanical ventilation.
Next, obtain IV access, consider starting IV fluids, and put your patient on continuous vital sign monitoring and cardiac telemetry.
Finally, start broad-spectrum antibiotics. If needed, manage increased intracranial pressure, which primarily relies on elevating the head of the bed, hyperventilation, sedation, and hyperosmolar therapy.
Now, let’s take a look at stable patients, starting with brain abscesses. In this case, obtain a focused history and physical exam, which is typically associated with headache, sometimes in combination with fever, confusion, seizure, or focal neurological symptoms, such as language impairment, vision changes, and limb weakness.

Stable Patient/Brain Abscess1:23–4:33

Patients may also have predisposing risk factors, including recent dental or neurosurgical procedures; penetrating head trauma; otitis media, mastoiditis, and sinusitis.
Another important risk factor is IV substance use, which is associated with an increased risk of hematogenous spread of pathogens throughout the body.
Lastly, patients might be immunocompromised, like from HIV infection, cancer, or organ transplantation; or they might have a congenital cardiac malformation with a right-to-left shunt.
This shunt allows pathogens to bypass the lungs and travel directly into the systemic circulation, eventually reaching the brain.
The physical exam may reveal altered mental status or focal neurological deficits. With these findings...
suspect a brain abscess, so obtain blood cultures as well as a CT or MRI of the brain. The blood cultures might identify a pathogen.
Brain imaging shows a ring-enhancing mass lesion with a central area of necrosis or pus, so diagnose a brain abscess. Next, begin empiric IV antibiotics, which will depend on the presumed source of infection and the patient’s history.
Brain abscesses are most commonly bacterial and caused by Streptococcus species, such as S. viridans and S.
pneumoniae. Anaerobic infections are also common and usually involve oropharyngeal or gastrointestinal organisms such as Bacteroides and Fusobacterium species.
Other common bacteria include Enterobacteriaceae, such as the Proteus mirabilis, E. coli, and Klebsiella pneumoniae species.
Finally, in immunocompromised individuals, think about Nocardia, Mycobacteria, or fungi like Aspergillus and Candida. Start with a third- or fourth-generation cephalosporin and metronidazole for anaerobic coverage.
If there is a history of direct penetrating trauma or neurosurgical procedure, add vancomycin for Staphylococcus aureus.
Also, consider starting an anti-seizure medication, and, if there’s significant brain edema, be sure to initiate corticosteroids.
Next, perform needle aspiration or surgical drainage of the abscess and send samples for cultures and PCR testing. Once you identify the underlying pathogen, tailor antibiotic treatment based on culture results.
Here’s a clinical pearl! Lumbar puncture is usually not indicated and is low yield.
It might even be contraindicated if there is concern for high intracranial pressure and brain herniation. Okay, let’s switch gears and talk about meningitis.

Meningitis4:33–8:09

These patients report headache and neck stiffness, typically in combination with fever and confusion. Additionally, history might reveal nausea and vomiting, sensitivity to light, and seizures.
When it comes to risk factors, you might find some clues that’ll point to the causative organism. There might have been a recent neurosurgical procedure or head trauma, in which case Staphylococcus aureus is a likely culprit.
On the flip side, if the patient had a recent infection such as pneumonia, otitis media, mastoiditis, or sinusitis, think Streptococcus pneumoniae.
Now, some patients might be immunocompromised or report chronic conditions such as diabetes, cirrhosis, or alcohol use disorder, in which case you should think of Listeria monocytogenes.
In addition, if your patient had their spleen removed or has functional asplenia from a condition like sickle cell disease, consider encapsulated microorganisms like Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae.
Finally, the patient might not be fully vaccinated, such as with the Neisseria meningitidis and Haemophilus influenzae type B vaccines.
Alright, on exam, you'll see signs of meningeal irritation, including nuchal rigidity; a positive Brudzinski sign, which refers to the flexion of the hip and knees when the neck is passively flexed; and a positive Kernig sign, which is pain on knee extension after holding the hip and knees in a flexed position.
Finally, you might notice altered mental status or focal neurological deficits. With these findings, suspect meningitis and assess for indications of brain CT.
These include altered mental status, immunocompromised states, focal neurological deficits, signs of increased intracranial pressure, such as Cushing triad, dilated pupil, or papilledema; history of CNS conditions, such as a mass lesion or stroke; and new seizures.
If any of these indications are present, obtain blood cultures and a brain CT. Next, initiate dexamethasone, which can decrease morbidity and mortality, and empiric intravenous antibiotics based on the patient’s demographic.
Between the ages of 2 and 50, the most common bacterial pathogens are Neisseria meningitidis and Streptococcus pneumoniae, so start vancomycin and a third-generation cephalosporin like ceftriaxone.
If the patient is over the age of 50, immunocompromised, or has an alcohol use disorder, there is also concern for Listeria monocytogenes and aerobic gram-negative bacilli.
In this case, combine vancomycin and a third-generation cephalosporin with ampicillin. Next, assess the imaging findings, and if there is no mass-occupying lesion causing increased intracranial pressure, perform a lumbar puncture and obtain a sample for CSF analysis, including cultures and PCR testing.
If the CSF analysis reveals elevated WBC count and a positive culture or PCR, diagnose meningitis. On the flip side, if there are no indications for brain CT, obtain blood cultures and a CSF sample for analysis, including cultures and PCR testing.
Again, start dexamethasone and empiric intravenous antibiotics. If the CSF analysis shows elevated white blood count and a positive culture or PCR, diagnose meningitis.

Tuberculous Meningitis8:09–8:55

Once you diagnose meningitis, assess the underlying cause. In tuberculous meningitis, the CSF analysis reveals elevated white blood cells, typically less than five hundred cells per microliter with a lymphocytic predominance, as well as decreased glucose-, and elevated protein levels.
Additional testing will reveal a positive acid-fast stain, while cultures and the nucleic acid amplification test will identify Mycobacterium tuberculosis.
With these findings, diagnose tuberculous meningitis. Next, discontinue the empiric antibiotics, and initiate tuberculosis-specific treatment known as RIPE therapy, which stands for rifampin, isoniazid, pyrazinamide, and ethambutol.
Next up is non-tuberculous bacterial meningitis. In this case, the CSF analysis reveals a WBC count greater than a thousand per microliter with neutrophilic predominance, decreased glucose, and elevated protein levels.

Non-tuberculous Bacterial Meningitis8:55–9:27

Next, the CSF culture will identify a specific bacterium, while blood cultures might be positive for the same pathogen. In this case, diagnose non-tuberculous bacterial meningitis, and tailor antibiotics based on culture results.

Viral Meningitis9:27–10:16

Now, moving on to non-bacterial causes of meningitis, starting with viral meningitis. In this case, the CSF profile can show a wide range of WBC counts, usually in the tens or hundreds, but occasionally up to a thousand per microliter, with a lymphocytic predominance.
Next, glucose levels will be normal or mildly decreased, and protein levels will be normal or mildly elevated. Finally, if the PCR testing identifies a specific virus, diagnose viral meningitis.
Treatment primarily relies on supportive care, but you can treat certain viruses with antiviral agents. For example, treat HSV and varicella zoster virus with acyclovir; and cytomegalovirus with ganciclovir or valganciclovir.

Cryptococcal Meningitis10:16–11:30

Finally, let's look at a specific fungal infection, cryptococcal meningitis, which typically affects immunocompromised patients, such as those with HIV or organ transplantation.
The most common cryptococcal species is Cryptococcal neoformans. The CSF analysis can reveal an elevated WBC count, but usually less than 500 per microliter.
Next, glucose levels will be normal or decreased, while protein levels will be normal or elevated. India ink stain will reveal encapsulated yeast because the ink does not penetrate the capsule around the cryptococcal cells, creating a halo effect.
Finally, the CSF cultures, cryptococcal antigen, or PCR testing will identify cryptococcus. With these findings, diagnose cryptococcal meningitis.
Stop empiric antibiotics and start induction therapy with IV amphotericin B and flucytosine. If your patient remains stable after two weeks, switch them to maintenance therapy with fluconazole.
Keep in mind that cryptococcal meningitis can be associated with elevated intracranial pressure and hydrocephalus, so some of these patients will need serial lumbar punctures.
Alright, as a quick recap… Meningitis is inflammation of the meninges, while a brain abscess refers to an encapsulated focal area of purulent infection within the brain parenchyma.

Review11:30–12:16

Once you suspect meningitis, be sure to obtain CSF analysis with cultures and PCR testing, which can help you differentiate between tuberculous-, non-tuberculous-, viral-, and cryptococcal meningitis.
Treatment primarily relies on empiric management until you identify a specific pathogen. On the flip side, once you suspect a brain abscess, obtain blood cultures and brain imaging to confirm the diagnosis.
Next, perform needle aspiration or surgical drainage of the abscess and obtain samples for cultures and PCR testing to identify