eMedicine Specialties > Emergency Medicine > Infectious Diseases
Meningitis: Differential Diagnoses & Workup
Updated: Jul 28, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
| Brain Abscess | Neoplasms, Brain |
| Delirium Tremens | Pediatrics, Febrile Seizures |
| Encephalitis | Pediatrics, Meningitis and Encephalitis |
| Herpes Simplex | Subarachnoid Hemorrhage |
| Herpes Simplex Encephalitis |
Other Problems to Be Considered
All causes of altered mental status and coma
Leptospirosis
Subdural empyema
Workup
Laboratory Studies
- Complete blood count (CBC) with differential
- Serum electrolytes to determine dehydration or syndrome of inappropriate secretion of antidiuretic hormone [SIADH])
- Serum glucose as baseline for determining normal CSF glucose; may be low if glycogen stores are depleted or high in infected patients with diabetes
- BUN and/or creatinine and liver profile to assess organ functioning and adjust antibiotic dosing
- Coagulation profile and platelets in patients with chronic alcohol use, liver disease, or if disseminated intravascular coagulation (DIC) is suspected. (Patients may require platelets or fresh frozen plasma [FFP] prior to LP.)
- Urinary electrolytes if SIADH is suspected
- Serum cryptococcal antigen, especially if baseline is known (less diagnostic than India ink and CSF cryptococcal antigen)
- Cultures prior to instituting antibiotics may be helpful if diagnosis is uncertain: blood (50% positive in meningitis caused by H influenzae, S pneumoniae, N meningitidis); nasopharynx, respiratory secretions, urine, and skin lesions.
- Latex agglutination or counter immunoelectrophoresis (CIE) of blood, urine, and CSF for specific bacterial antigens is recommended occasionally if diagnosis is challenging or in patients with partially treated meningitis.
- Serum test for syphilis is indicated if neurosyphilis is in differential diagnosis. (Cases have been documented of neurosyphilis CSF negative for Venereal Disease Research Laboratory test [VDRL].)
Imaging Studies
- Head CT scan with contrast or MRI with gadolinium
- Imaging is indicated in patients with evidence of head trauma, altered mental status, or focal findings.
- Presence of papilledema and inability to fully assess fundi or neurologic status are indications for CT scan prior to LP.
- Obtain blood cultures and initiate treatment before imaging studies and LP in patients with suspected bacterial meningitis.
- Results may be normal or demonstrate small ventricles, effacement of sulci, and contrast enhancement over convexities.
- Late findings include venous infarction and communicating hydrocephalus.
- Rule out brain abscess, sinus or mastoid infection, skull fracture, and congenital anomalies.
Acute bacterial meningitis (same patient as in Media files 2-3). This axial nonenhanced computed tomography scan shows mild ventriculomegaly and sulcal effacement.
Acute bacterial meningitis (same patient as in Media files 1 and 3). This axial T2-weighted magnetic resonance image shows only mild ventriculomegaly.
Acute bacterial meningitis (same patient as in Media files 1-2). This contrast-enhanced, axial T1-weighted magnetic resonance image shows leptomeningeal enhancement (arrows).
- Chest radiography
- As many as 50% of patients with pneumococcal meningitis also have evidence of pneumonia on initial chest radiograph.
- This association occurs in fewer than 10% of patients with meningitis caused by H influenzae or N meningitidis and in approximately 20% of patients with meningitis caused by other organisms.
Procedures
- Lumbar puncture (see Table 1 for interpretation of results)
- Elevated opening pressure correlates with increased risk of morbidity and mortality in bacterial and fungal meningitis.
- Take tube #1 to chemistry lab for glucose and protein.
- Take tube #2 to hematology lab for cell count with differential.
- Take tube #3 to microbiology and immunology lab for Gram stain, bacterial culture, acid-fast bacillus (AFB) stain and tuberculosis (TB) cultures, India ink stain and fungal cultures, CIE, VDRL, and cryptococcal antigen, if indicated.
- Hold tube #4 for repeat cell count with differential, if needed (or for other subsequent studies not initially ordered).
- Research correlates CSF cytokines in children with bacterial meningitis.
- According to Seupaul, 3 diagnostic tests have clinically useful likelihood ratios for the diagnosis of bacterial meningitis in adults: CSF/blood glucose ratio less or equal to 0.4, CSF WBC count greater or equal to 500/L, and CSF lactate level equal or greater than 31.53.4
- General patterns in CSF pressure measurement and analysis in bacterial, viral, and fungal (cryptococcal) meningitis may support a diagnosis. The most important diagnostic tests in the ED to rule out bacterial meningitis are a well-performed Gram stain and, if available, polymerase chain reaction (PCR) on the CSF of patients with suspected herpes simplex encephalitis.
Table 1. Comparison of CSF Findings by Type of Organism
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Table
| Bacterial Meningitis | Viral Meningitis* | Fungal Meningitis** | |
|---|---|---|---|
| Pressure 5-15 cm H2 O | Increased | Normal or mildly increased | Normal or mildly increased in TB. May be increased in fungal. AIDS patients with cryptococcal meningitis have increased risk of blindness, death unless maintained at <30 cm. |
| Cell count preterm: 0-25 term: 0-22 >6 months: 0-5 mononuclear cells/mm3 | No cell count result can exclude bacterial meningitis. Typically thousands of PMNs, but may be less dramatic or even normal (classically, in very early meningococcal meningitis and in extremely ill neonates). Lymphocytosis with normal CSF chemistries seen in 15-25%, especially when cell counts <1000 or if partially treated. Approximately 90% of patients with ventriculoperitoneal shunts have CSF WBC count >100 cells/mm3 are infected; CSF glucose usually normal, and organisms are less pathogenic. Cell count and chemistries normalize slowly (over days) with antibiotics. | Usually <500 cells, nearly 100% mononuclear. Up to 48 hours, significant PMN pleocytosis may be indistinguishable from early bacterial meningitis; this is particularly true with eastern equine encephalitis. Presence of nontraumatic RBCs in 80% of HSV meningoencephalitis, although 10% have normal CSF results | Hundreds of mononuclear cells |
| Micro no organisms | Gram stain 80% effective. Inadequate decolorization may mistake H influenzae for gram-positive cocci. Pretreatment with antibiotics may affect stain uptake, causing gram-positive organisms to appear gram negative and decrease culture yield on average 20%. | No organism | India ink 80-90% effective for fungi; AFB stain 40% effective for TB (increase yield by staining supernate from at least 5 cc CSF) |
| Glucose euglycemia: >50% serum hyperglycemia: >30% serum wait 4 h after glucose load | Decreased | Normal | Sometimes decreased. Aside from fulminant bacterial meningitis, the lowest levels of CSF glucose are seen in TB, primary amebic meningoencephalitis, neurocysticercosis |
| Protein preterm: 65-150 term: 20-170 >6 months: 15-45 mg/dL | Usually >150, may be >1000 | Mildly increased | Increased; >1000 with relatively benign clinical presentation suggestive of fungal disease |
| Bacterial Meningitis | Viral Meningitis* | Fungal Meningitis** | |
|---|---|---|---|
| Pressure 5-15 cm H2 O | Increased | Normal or mildly increased | Normal or mildly increased in TB. May be increased in fungal. AIDS patients with cryptococcal meningitis have increased risk of blindness, death unless maintained at <30 cm. |
| Cell count preterm: 0-25 term: 0-22 >6 months: 0-5 mononuclear cells/mm3 | No cell count result can exclude bacterial meningitis. Typically thousands of PMNs, but may be less dramatic or even normal (classically, in very early meningococcal meningitis and in extremely ill neonates). Lymphocytosis with normal CSF chemistries seen in 15-25%, especially when cell counts <1000 or if partially treated. Approximately 90% of patients with ventriculoperitoneal shunts have CSF WBC count >100 cells/mm3 are infected; CSF glucose usually normal, and organisms are less pathogenic. Cell count and chemistries normalize slowly (over days) with antibiotics. | Usually <500 cells, nearly 100% mononuclear. Up to 48 hours, significant PMN pleocytosis may be indistinguishable from early bacterial meningitis; this is particularly true with eastern equine encephalitis. Presence of nontraumatic RBCs in 80% of HSV meningoencephalitis, although 10% have normal CSF results | Hundreds of mononuclear cells |
| Micro no organisms | Gram stain 80% effective. Inadequate decolorization may mistake H influenzae for gram-positive cocci. Pretreatment with antibiotics may affect stain uptake, causing gram-positive organisms to appear gram negative and decrease culture yield on average 20%. | No organism | India ink 80-90% effective for fungi; AFB stain 40% effective for TB (increase yield by staining supernate from at least 5 cc CSF) |
| Glucose euglycemia: >50% serum hyperglycemia: >30% serum wait 4 h after glucose load | Decreased | Normal | Sometimes decreased. Aside from fulminant bacterial meningitis, the lowest levels of CSF glucose are seen in TB, primary amebic meningoencephalitis, neurocysticercosis |
| Protein preterm: 65-150 term: 20-170 >6 months: 15-45 mg/dL | Usually >150, may be >1000 | Mildly increased | Increased; >1000 with relatively benign clinical presentation suggestive of fungal disease |
*Some bacteria (eg, Mycoplasma, Listeria, Leptospira species, Borrelia burgdorferi [Lyme], spirochetes) produce spinal fluid alterations that resemble the viral profile. An aseptic profile also is typical of partially treated bacterial infections (more than 33% of patients have received antimicrobial treatment, especially children) and the 2 most common causes of encephalitis — the potentially curable HSV and arboviruses.
**In contrast, TB meningitis and parasites resemble the fungal profile more closely.
More on Meningitis |
| Overview: Meningitis |
 Differential Diagnoses & Workup: Meningitis |
| Treatment & Medication: Meningitis |
| Follow-up: Meningitis |
| Multimedia: Meningitis |
| References |
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References
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Further Reading
Keywords
inflammation of the leptomeninges, inflammation of the underlying subarachnoid cerebrospinal fluid, bacterial meningitis, meningococcal meningitis, pneumococcal meningitis, Neisseria meningitidis, N meningitidis, Streptococcus pneumoniae, S pneumoniae, Listeria monocytogenes, L monocytogenes, group B streptococci, Haemophilus influenzae, H influenzae , Haemophilus influenzae type b, H influenzae type b, brain edema, nuchal rigidity, fungalmeningitis, tuberculous meningitis, Kernig sign, Brudzinski sign, papilledema, increased intracranial pressure, increased ICP
