Does the absence of fever and leukopenia (low white blood cell count) rule out meningitis?

Absence of Fever and Low White Count in Meningitis Diagnosis

The absence of fever and low white blood cell count does not rule out meningitis, as classic clinical characteristics may be absent in patients with bacterial meningitis. 1

Clinical Presentation of Meningitis

• Fever is a common but not universal finding in meningitis, reported in 77-97% of adult bacterial meningitis cases, meaning 3-23% of patients may present without fever 1
• The classic triad of fever, neck stiffness, and altered mental status is present in only 41-51% of bacterial meningitis cases 1
• Clinical signs have low diagnostic accuracy for predicting meningitis:
  • Neck stiffness (sensitivity 31%)
  • Brudzinski sign (sensitivity 9%)
  • Kernig sign (sensitivity 11%) 1
• No single clinical sign of bacterial meningitis is present in all patients 1

Importance of CSF Analysis

• Cerebrospinal fluid (CSF) examination remains the cornerstone of diagnosis for suspected meningitis, regardless of the presence or absence of classic symptoms 1, 2
• CSF analysis is the principal contributor to the final diagnosis of meningitis with the highest diagnostic accuracy 1
• CSF white blood cell count is the best diagnostic parameter for differentiating bacterial meningitis from other diagnoses (area under curve 0.95) 1

Atypical Presentations

• Bacterial meningitis can present solely with nonspecific symptoms, with characteristic clinical signs being completely absent 1
• Cases of culture-confirmed bacterial meningitis without CSF pleocytosis (normal white cell count in CSF) have been reported, though rare 3, 4
• A systematic review identified 124 cases of meningitis without CSF pleocytosis, with bacterial organisms being the most common cause (99 cases) 3
• Fulminant bacterial meningitis can occur without any meningeal signs, even in previously healthy adults 5

Risk Factors and Special Populations

• Certain populations are at higher risk for atypical presentations:
  • Neonates often present with nonspecific symptoms 1
  • Immunocompromised patients may have blunted inflammatory responses 1
  • Elderly patients may present without classic symptoms 4
• Listeria monocytogenes, the third most common cause of bacterial meningitis overall, is particularly common in immunocompromised patients and the elderly 1

Diagnostic Algorithms

• No published diagnostic algorithm for distinguishing bacterial from viral meningitis has 100% sensitivity 1
• Every algorithm will fail to recognize a proportion of bacterial meningitis patients 1
• Clinician judgment should be used to estimate the risk of bacterial meningitis rather than relying solely on algorithms 1

Clinical Implications

• The ESCMID strongly recommends CSF examination in all children with suspected bacterial meningitis, unless contraindications for lumbar puncture are present 1
• In adults with suspected bacterial meningitis, meningitis should not be ruled out solely based on the absence of classic symptoms 1
• When meningitis is suspected, empiric antibiotics should be administered regardless of initial white blood cell count on lumbar puncture 3

Pitfalls to Avoid

• Do not rule out meningitis based solely on absence of classic symptoms, as these may not be present in all cases 2
• Do not rely on Kernig's sign or Brudzinski's sign alone due to their low sensitivity 2, 6
• Do not delay antimicrobial therapy if bacterial meningitis is suspected while awaiting imaging or lumbar puncture 2
• Do not assume normal CSF cell count excludes infection; early in the course of illness, CSF white cell count may be minimal or absent 2, 3

In conclusion, while fever and elevated white blood cell count are common findings in meningitis, their absence does not exclude the diagnosis. Lumbar puncture for CSF analysis remains essential when meningitis is clinically suspected, regardless of the presence or absence of typical signs and symptoms.