Meningitis and brain abscess: Clinical sciences

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. 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.

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. 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.