Meningitis is the inflammation of the leptomeninges, typically indicated by an abnormal white blood cell count in cerebrospinal fluid (CSF), with bacterial forms being the most common and often presenting with fever, neck stiffness, and altered mental status. Diagnosis involves lumbar puncture and analysis of CSF, alongside blood cultures, with immediate empiric antibiotic therapy recommended upon suspicion. Viral meningitis, primarily caused by enteroviruses and HSV, presents with distinct CSF profiles and requires specific treatment approaches.

1. Meningitis
‫بصیری‬ ‫هومن‬
1403

2. INTRODUCTION
Meningitis is an inflammatory disease of the leptomeninges, the tissues
surrounding the brain and spinal cord, and is defined by an abnormal
number of white blood cells in the cerebrospinal fluid (CSF)
Approximately 1.2 million cases of bacterial meningitis occur annually
worldwide

3. EPIDEMIOLOGY
Bacterial meningitis can be community-acquired or healthcare-
associated
The major causes of community-acquired bacterial meningitis in adults
in developed countries are Streptococcus pneumonia , Neisseria
meningitides , and, primarily in patients over age 50 to 60 years or those
who have deficiencies in cell-mediated immunity, Listeria
monocytogenes
The major causes of healthcare-associated bacterial meningitis are
different (usually staphylococci and aerobic gram-negative bacilli)
Healthcare-associated bacterial meningitis may also occur in patients
with internal or external ventricular drains, or following trauma

4. CLINICAL FEATURES
Patients with bacterial meningitis are usually quite ill and often present
soon after symptom onset

5. Presenting manifestations
The classic triad of acute bacterial meningitis consists of fever, nuchal
rigidity, and a change in mental status, although an appreciable number
of patients do not have all three features
Most patients have high fevers, often greater than 38ºC but a small
percentage have hypothermia
Headache is also common
However, virtually all patients have at least one of the findings of the
classic triad of fever, neck stiffness, and altered mental status
the absence of all of these findings essentially excludes the presence of
bacterial meningitis

6. Neurologic complications such as seizures, focal neurologic deficits
(including cranial nerve palsies), and papilledema may be present early
or occur later in the course
Certain bacteria, particularly N. meningitides , can cause characteristic
skin manifestations, such as petechiae and palpable purpura
Arthritis occurs in some patients with bacterial meningitis

7. Examination for nuchal
rigidity
Passive or active flexion of the neck will usually result in an inability to
touch the chin to the chest
The classic Brudzinski's sign refers to spontaneous flexion of the hips
during attempted passive flexion of the neck
The Kernig's sign refers to the inability or reluctance to allow full
extension of the knee when the hip is flexed 90º

8. LABORATORY FEATURES

9. Laboratory studies
Routine blood work is often unrevealing. The white blood cell count is
usually elevated, with a shift toward immature forms; however, severe
infection can be associated with leukopenia. The platelet count may also
be reduced

10. Blood cultures
Blood cultures are often positive and can be useful in the event that CSF
cannot be obtained before the administration of antimicrobials.
Approximately 50 to 90 percent of patients with bacterial meningitis
have positive blood cultures
Two sets of blood cultures should be obtained from all patients prior to
the initiation of antimicrobial therapy.

11. LUMBAR PUNCTURE
Every patient with suspected meningitis should have CSF obtained
unless lumbar puncture (LP) is contraindicated
It is not uncommon for LP to be delayed while a computed tomographic
(CT) scan is performed to exclude a mass lesion or increased intracranial
pressure, which rarely leads to cerebral herniation during subsequent
CSF removal. However, a screening CT scan is not necessary in the
majority of patients

12. Indications for CT scan before LP
a CT scan of the head before LP should be performed in adult patients
with suspected bacterial meningitis who have one or more of the
following risk factors
•Immunocompromised state (eg, HIV infection, immunosuppressive
therapy, solid organ or hematopoietic stem cell transplantation)
•History of CNS disease (mass lesion, stroke, or focal infection)
•New onset seizure (within one week of presentation)
•Papilledema
•Abnormal level of consciousness
•Focal neurologic deficit

13. If LP is delayed
If LP is delayed or deferred, blood cultures should be obtained and
antibiotics should be administered empirically before the imaging study,
followed as soon as possible by the LP. In
addition, dexamethasone (0.15 mg/kg IV every six hours) should be
given shortly before or at the same time as the antibiotics if the
preponderance of clinical and laboratory evidence suggests bacterial
meningitis with a plan to stop therapy, if indicated, when the evaluation
is complete. Adjunctive dexamethasone should not be given to patients
who have already received antimicrobial therapy because it is unlikely to
improve patient outcome

14. Opening pressure
he opening pressure is typically elevated in patients with bacterial
meningitis

15. CSF analysis
The usual CSF findings in patients with bacterial meningitis are a white
blood cell count of 1000 to 5000/microL (range of <100 to >10,000) with
a percentage of neutrophils usually greater than 80 percent, protein of
100 to 500 mg/dL, and glucose <40 mg/dL (with a CSF:serum glucose
ratio of ≤0.4).

16. Gram stain
•Gram-positive diplococci suggest pneumococcal infection
•Gram-negative diplococci suggest meningococcal infection)
•Small pleomorphic gram-negative coccobacilli suggest Haemophilus
influenzae infection
• Gram-positive rods and coccobacilli suggest listerial infection

17. Polymerase chain reaction
Nucleic acid amplification tests, such as the polymerase chain reaction
(PCR), have been evaluated in patients with bacterial meningitis

18. GENERAL PRINCIPLES OF
THERAPY

19. Avoidance of delay
Antibiotic therapy, along with adjunctive dexamethasone when
indicated, should be initiated immediately after the performance of the
lumbar puncture (LP) or, if a computed tomography (CT) scan of the
head is to be performed before LP, immediately after blood cultures are
obtained

20. Choice of regimen
Antibiotic selection must be empiric immediately after CSF is obtained
or when lumbar puncture is delayed. In such patients, antibiotic therapy
needs to be directed at the most likely bacteria based upon patient age
and underlying comorbid disease
Once the CSF Gram stain results are available, the antibiotic regimen
should be tailored to cover the most likely pathogen

21. Route of administration
Because of the general limitation in antibiotic penetration into the CSF,
all patients should be treated with intravenous antibiotics

22. Adjunctive dexamethasone
Early intravenous administration of glucocorticoids
(usually dexamethasone ) has been evaluated as adjunctive therapy in
an attempt to diminish the rate of hearing loss, other neurologic
complications, and mortality

23. Empiric regimens

25. REGIMENS BASED UPON
GRAM STAIN

27. VIRAL MENINGITIS

28. Enteroviruses
Aseptic meningitis occurring during the summer or fall is most likely to
be caused by enteroviruses (eg, Coxsackie, echovirus, other non-
poliovirus enteroviruses), the most common cause of viral meningitis
The presenting signs and symptoms of enteroviral meningitis are not
distinctive
Cerebrospinal fluid (CSF) findings are typical of other viral meningitides
and include a white blood cell (WBC) count that is generally less than
250 cells/microL, a modest elevation in CSF protein concentration
(generally less than 150 mg/dL), and a normal glucose concentration

29. HIV infection
The CSF profile characteristically has a lymphocytic pleocytosis, an
elevated protein concentration, and normal glucose concentration

30. Herpes simplex meningitis
Primary HSV has been increasingly recognized as a cause of viral
meningitis in adults. In contrast to HSV encephalitis, which is almost
exclusively due to HSV-1, viral meningitis in immunocompetent adults is
generally caused by HSV-2
There is no standard approach to the treatment of HSV meningitis For
hospitalized patients, we prefer intravenous acyclovir at
10 mg/kg administered every eight hours. Patients can be switched to
an oral agent on discharge for a total of 10 to 14 days of treatment.

31. Recurrent (Mollaret's)
meningitis
The most common etiologic agent in Mollaret's meningitis is HSV-2,
although some patients do not have evidence of genital lesions at the
time of presentation

32. Mumps
The most frequent manifestations are headache, low-grade fever, and
mild nuchal rigidity. The onset of meningitis is variable and can occur
before, during, or after an episode of mumps parotitis
The CSF profile typically reveals fewer than 500 WBC/microL with a
lymphocytic predominance, but more than 1000 WBC/microL and an
early neutrophil predominance can occasionally be seen. The CSF total
protein is generally normal or mildly elevated and the CSF glucose levels
may be mildly depressed.