There’s nothing that gets a hospitalist more anxious and excited at the same time than a case of suspected meningitis. In this episode, we learn that if the thought crosses our mind, a lumbar puncture is almost certainly indicated. Our guest, Dr. Payal Patel, helps us with the balancing act that is diagnosing and managing meningitis!
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Per Dr. Patel, some keys to differentiate meningitis from meningoencephalitis include personality changes or decreased level of consciousness (i.e. increased sleepiness), recent-onset seizures, or coma, all of which are concerning for encephalitis. On exam, papilledema and focal neurologic findings can also be clues for encephalitis.
Diagnosis and management must occur concurrently in cases of possible meningitis in order to provide timely care, though they will be covered separately here.
When meningitis is suspected, lumbar puncture should be performed to obtain cerebrospinal fluid as soon as possible. However, there are some steps that should precede the procedure. Blood cultures should be obtained immediately, as bacteremia often accompanies meningitis. Once these are obtained, empiric therapy (which is addressed later) should be started. A frequent point of confusion is whether a CT head is necessary prior to lumbar puncture. In most cases, it is not required, but there are some instances in which a CT head should be obtained first. These instances include advanced age, prior history of CNS disease (brain metastases), or immunocompromise. A more thorough list of criteria can be found in the IDSA guidelines for meningitis. [Tunkel, et al 2004]
Once CSF is obtained, the bare minimum for testing includes cell count with differential, gram stain with culture, protein, and glucose. The most important thing according to Dr. Patel is the white blood cell count: a normal person would have zero to one WBC. If the number is anything above 5 WBCs, this is concerning for meningitis. If the WBC is very high, the common causes of bacterial meningitis are more likely. As that number decreases, the differential diagnosis becomes broader and includes rare bacterial sources as well as viral etiologies.
While initial testing with cell count and gram stain is key in developing a treatment plan, advanced diagnostics/panel PCR testing can be useful for diagnosing the most common pathogens–Strep, Haemophilus, and Neisseria species, especially in patients who have already received antibiotics. As such, this type of testing can be helpful in determining when to initiate or stop antibiotics. [Tunkel, et al 2004]]
Dr. Patel says that when obtaining CSF, it is important to try to secure more fluid than is required for the initial work-up in case additional studies are needed. When bacterial work-up is negative, Dr. Patel advises testing for other pathogens. These should include fungal and viral studies and sometimes may include universal PCR testing or meta genomic next-generation sequencing. If these tests are also negative, a diagnosis of aseptic meningitis should be considered.
An astute listener pointed out that we incorrectly referred to the sensitivity and specificity of PCR tests in the segment from 22:17 – 24:17. Because we were making a point about situations in which the utility of diagnostic tests depends on disease prevalence, we should have referred to the negative predictive value (NPV) and positive predictive value (PPV) instead. In general, sensitivity and specificity of PCR tests are high regardless of disease prevalence.
The most important thing in management is starting antibiotics ASAP, as delay increases morbidity and mortality. As mentioned above, it is key to obtain blood cultures prior to administering antibiotics[Tunkel, et al 2004].
When selecting empiric coverage, it is important to take into account patient risk factors for specific pathogens (e.g. immunocompromise, advanced age, recent neurosurgery). [Tunkel, et al 2004]
The guiding principles to choosing antibiotics include determining what the potential causative organisms are for a particular patient as well as accounting for which antibiotics cross the blood-brain barrier. In the case of community acquired infections, an appropriate empiric regimen includes vancomycin and ceftriaxone [Tunkel, et al 2004]. Over time, strep has become resistant to ceftriaxone, hence the recommendation to add vancomycin. If the infection is found to be MSSA, the treatment can be narrowed to nafcillin. Ceftriaxone also covers gram-negative causes as well. [Tunkel, et al 2004]
In older patients (>50 years), the incidence of listeria meningitis is higher and requires ampicillin, as ceftriaxone is not effective against listeria. Notably, listeria is frequently associated with bacteremia. [Tunkel, et al 2004]]
Hospital-acquired infections include MRSA and Pseudomonas spp. Appropriate choices for such infections are vancomycin, cefepime or ceftazidime. [Tunkel, et al 2004]
Steroids (traditionally dexamethasone) are helpful in the early stages of strep pneumo meningitis. They should be administered before or with antibiotics. After this initial period, steroids are less not effective. The mechanisms of action of steroids are thought to include decreasing cerebral edema and intracranial pressure, and mitigating other effects of inflammation due to pro-inflammatory cytokine expression [Tunkel, et al 2004]. In high-income countries, steroids are effective at reducing hearing loss and short-term neurologic sequelae when given with or before antibiotics in patients with Strep pneumoniae infections but not Haemophilus or Neisseria infections. In lower-income countries, steroids have not been shown to be beneficial [Brouwer M, et al 2015].
Dr. Patel notes it is okay to start antivirals initially, but once CSF results have returned, use the information to decide whether they are needed. If you have a lymphocytic predominance in the CSF but PCR is negative for HSV, consider a repeat LP if your suspicion is high enough to continue antivirals.
Length of treatment is dependent on pathogen as well as presence or absence of bacteremia. Duration in treatment of meningitis is not as well studied, and consulting Infectious Disease is recommended to determine the best course for your patients. For simple, non-bacteremic infections, 10-14 days of antibiotics are appropriate. Regarding steroids, these should be administered for the first four days of treatment of strep infections only. [Tunkel, et al 2004]]
Up to 40% of patients can have neurologic sequelae following a course of meningitis, and patients should be counseled on this. These can include hearing loss (though this is more common in children). Mortality in meningitis was as high as 95% before antibiotics. Since the advent of antibiotics, mortality is as low as 7%. Before vaccines, deafness and other neurologic complications were more prevalent. Since the advent of vaccines, these have decreased significantly.
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Listeners will learn the steps in diagnosing and managing bacterial meningitis
After listening to this episode listeners will be able to
Dr. Patel reports a previous association with Qiagen. This relationship has ended. The Curbsiders report no relevant financial disclosures.
Amin M, Trubitt M, Watto MF, Patel PK. “#347 Meningitis”. The Curbsiders Internal Medicine Podcast. http://thecurbsiders.com/episode-list Final publishing date July 25, 2022
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