What is the diagnostic approach for an adult patient with no significant past medical history presenting with symptoms suggestive of meningitis, such as headache, fever, stiff neck, and confusion?

Diagnostic Approach for Suspected Meningitis in Adults

Immediately arrange emergency ambulance transport to hospital (ideally within one hour) and initiate empiric antibiotics without delay if bacterial meningitis is suspected, regardless of whether imaging or lumbar puncture has been performed. 1, 2

Initial Clinical Assessment

Document the presence or absence of these key features at presentation:

• Headache, fever, neck stiffness, and altered mental status are the four cardinal symptoms—95% of patients have at least two of these four symptoms, though the classic triad (fever, neck stiffness, altered mental status) occurs in only 41-51% of cases 1, 2, 3
• Rash of any description, particularly petechial or purpuric patterns (present in 20-52% of cases; when present with meningitis, indicates meningococcus in >90% of cases) 1, 2, 4
• Seizures (occur in 10-25% of adults) 2
• Focal neurologic deficits (present in 11-34% of cases) 1, 4
• Signs of shock including hypotension and poor capillary refill 1

Critical Diagnostic Pitfalls to Avoid

Do not rely on Kernig's sign or Brudzinski's sign to rule out meningitis—these have extremely poor sensitivity (5-11%) and will miss the vast majority of actual cases 1, 4. Similarly, neck stiffness has only 31% sensitivity, meaning it is absent in 69% of confirmed cases 1, 2, 4.

Never exclude bacterial meningitis based solely on absence of classic symptoms, as characteristic clinical signs may be completely absent 1.

Age-Specific Considerations

• Elderly patients (>65 years) are less likely to present with fever or neck stiffness but more likely to have altered consciousness 2
• Patients >50 years, immunocompromised, alcoholic, or diabetic require coverage for Listeria monocytogenes 2

Immediate Management Algorithm

Step 1: Empiric Antibiotic Initiation (Do Not Delay)

Start antibiotics immediately upon clinical suspicion, before any diagnostic testing:

Standard regimen:

• Ceftriaxone 2g IV every 12 hours for S. pneumoniae and N. meningitidis 2, 5

Add ampicillin 2g IV every 4 hours if:

• Age >50 years
• Immunocompromised status
• Alcoholism
• Diabetes
• Any condition requiring Listeria coverage 2

Add vancomycin if septic cavernous sinus thrombosis is suspected (most commonly caused by S. aureus including CA-MRSA) 2

Step 2: Cerebrospinal Fluid Analysis

CSF examination remains the principal diagnostic test with the highest accuracy (AUC 0.95) for bacterial meningitis 2. Perform lumbar puncture promptly unless contraindications exist.

Consider imaging before LP only if:

• Focal neurologic deficits are present
• Papilledema is identified
• Severely altered consciousness (GCS <10)
• Concern for mass effect or increased intracranial pressure

Step 3: Additional Diagnostic Considerations

• Obtain blood cultures before antibiotics when possible, but do not delay treatment 3
• Document any source of infection such as otitis media or sinusitis (associated with worse outcomes) 3
• Assess for travel history and contact with other meningitis cases 1
• Consider tuberculosis meningitis in patients with subacute onset and cranial nerve palsies (particularly sixth nerve), especially if risk factors present 6

Prognostic Factors Associated with Unfavorable Outcomes

Risk factors indicating higher mortality and morbidity include:

• Advanced age
• Presence of otitis or sinusitis
• Absence of rash (paradoxically worse prognosis)
• Low Glasgow Coma Scale score on admission
• Tachycardia
• Positive blood culture
• Elevated erythrocyte sedimentation rate
• Thrombocytopenia
• Low CSF white-cell count
• S. pneumoniae infection (30% mortality vs. 7% for meningococcal) 3

Special Clinical Scenarios

Meningococcal sepsis can present with hypotension, altered mental state, and rash; patients can deteriorate rapidly with shock ensuing—this requires the same urgent antibiotic approach plus aggressive hemodynamic support 1, 4.

Concern from either the referring physician or a family member should always be taken seriously, even when classic features are absent 1.