What is meningitis, its causes, symptoms, and treatment?

Meningitis: Pathophysiology, Causes, Symptoms, and Treatment

Definition and Pathophysiology

Meningitis is an inflammation of the meninges—the protective membranes surrounding the brain and spinal cord—that can be caused by bacterial, viral, or fungal infections 1, 2. The inflammatory response in the meninges triggers the characteristic clinical syndrome, with bacterial forms being rapidly fatal if untreated, while viral forms are typically self-limited 1, 3.

Causes

Bacterial Meningitis

The most common bacterial pathogens in adults include:

• Streptococcus pneumoniae (pneumococcus) - most prevalent in adults, particularly those >50 years 4, 5
• Neisseria meningitidis (meningococcus) - presents with characteristic purpuric rash in 92% of cases 4
• Listeria monocytogenes - critical consideration in adults >50 years and immunocompromised patients 4, 5
• Haemophilus influenzae - less common in adults due to vaccination 6, 7

Viral Meningitis

Viral meningitis accounts for 50-80% of all meningitis cases 8, 9:

• Enteroviruses - most common cause, transmitted via fecal-oral route 8, 9
• Herpes simplex virus type 2 (HSV-2) - sexually transmitted, can occur without concurrent genital ulcers 8
• Varicella zoster virus (VZV) - can occur with or without rash 8
• Other viruses - HSV-1, cytomegalovirus, Epstein-Barr virus, mumps 8

Risk Factors and Predisposing Conditions

• Asplenia or splenic dysfunction - increased risk of pneumococcal infection 8
• Complement deficiency or Eculizumab therapy - increased risk of meningococcal infection 8
• HIV infection - higher incidence and mortality for both pneumococcal and meningococcal meningitis 8
• CSF leak from trauma or neurosurgery 8
• Recent facial bone fractures - can predispose to pneumococcal meningitis 10

Clinical Presentation

Classic Symptoms

Less than 50% of patients present with the complete classic triad, making diagnosis challenging 4, 3:

• Headache - present in 66% of cases 4, 5
• Fever - present in 74-84% of cases 4
• Neck stiffness/meningism - variable presentation 4
• Altered mental status - present in approximately 52% 4

Additional Common Symptoms

• Photophobia - characteristic of meningeal irritation 8, 4
• Vomiting and seizures - frequently observed 4
• General fatigue - present in 53% of cases 5
• Purpuric rash - highly specific for meningococcal disease (92% of N. meningitidis cases) 4

Atypical Presentations

Elderly patients often present differently 4:

• More altered mental status
• Less neck stiffness
• Less fever
• Higher mortality risk 5

Viral Meningitis Specific Features

Patients with viral meningitis present with meningism but typically without reduced consciousness 8:

• Fever may be absent 8
• Non-specific symptoms including diarrhea, muscle pain, sore throat 8
• Altered consciousness suggests alternative diagnosis such as bacterial meningitis or encephalitis 8

Diagnostic Approach

Immediate Clinical Assessment

Document the following critical features 4:

• Presence or absence of headache, altered mental status, neck stiffness
• Fever, rash characteristics, seizures
• Signs of shock or cardiovascular instability

Lumbar Puncture and CSF Analysis

Brain imaging (CT or MRI) before lumbar puncture is indicated when 4:

• Focal neurological deficits present
• New-onset seizures
• Severely altered mental status (GCS ≤12)
• Severely immunocompromised state

For viral meningitis diagnosis 8, 9:

• CSF PCR is the gold standard for confirmation 8
• Test for enterovirus, HSV-1, HSV-2, and VZV 8
• Stool and/or throat swabs for enterovirus PCR 8
• No cause found in 30-50% of presumed viral cases 8

Blood Cultures and Additional Testing

If lumbar puncture is delayed, obtain blood cultures and start empiric antibiotics immediately 4

All patients with meningitis should have HIV testing 8:

• HIV prevalence in culture-negative meningitis is 1-5% 8
• Consider HIV RNA PCR if antibody test negative but suspicion high 8

Treatment

Bacterial Meningitis - Immediate Antibiotic Therapy

Antibiotics must be started within 1 hour of clinical suspicion 4

Empiric antibiotic regimen for adults aged 18-50 years 4:

• Ceftriaxone 2g IV every 12 hours OR Cefotaxime 4, 6, 7
• PLUS Vancomycin or rifampicin 4

For adults >50 years or immunocompromised 4:

• Add Ampicillin/Amoxicillin/Penicillin G to cover Listeria monocytogenes 4
• This addition is critical and commonly overlooked 4

Adjunctive Dexamethasone Therapy

Dexamethasone should be used in bacterial meningitis 4:

• Stop dexamethasone if Listeria monocytogenes is confirmed 4

Viral Meningitis Treatment

Treatment is primarily supportive care, as there are no proven treatments for most viral causes 8, 9:

• Analgesia for headache and other symptoms 9
• Adequate hydration with IV or oral fluids 9
• Discontinue antibiotics once viral diagnosis confirmed 9
• Expedite hospital discharge once diagnosis established 9

Aciclovir/Valaciclovir is NOT recommended for HSV or VZV meningitis 8, 9:

• No evidence supports antiviral treatment for herpes meningitis 8, 9
• However, if encephalitis is suspected, immediately administer IV aciclovir 9

For recurrent HSV-2 meningitis 9:

• Prophylactic aciclovir/valaciclovir is NOT recommended 9
• Did not reduce recurrence in placebo-controlled trials 9

Critical Care Management

Intensive Care Indications

ICU referral is indicated for 4:

• Rapidly evolving rash
• GCS ≤12
• Cardiovascular instability
• Respiratory compromise
• Frequent seizures
• Altered mental state

Intubation should be strongly considered for GCS <12 4

Hemodynamic Management

• Maintain euvolemia with crystalloids as initial fluid choice 4
• Target mean arterial pressure ≥65 mmHg 4

Complications and Long-Term Sequelae

Bacterial Meningitis Outcomes

Neurological deficits occur in 50% of adults 4:

• Hearing loss - occurs in 5-35% of patients 4
• Cognitive deficits 4
• Seizures 4
• Motor deficits 4
• Visual disturbances 4
• Case fatality rate can be as high as 20% for all bacterial causes and 30% for pneumococcal meningitis 3

Viral Meningitis Outcomes

Viral meningitis is rarely fatal in immunocompetent adults 9:

• Most patients make full recovery 9
• Headaches - most common long-term sequela, affecting up to one-third 9
• Fatigue, sleep disorders, emotional difficulties 9
• May require staged return to work or studies 9

Follow-Up Care

All patients should be assessed for sequelae before discharge 8, 9:

• Many issues only become apparent after discharge 8
• Follow-up care should be offered to all with confirmed or probable bacterial meningitis 8

Prevention and Prophylaxis

Meningococcal Meningitis Contacts

Chemoprophylaxis for close contacts is essential 4:

• Close contacts defined as prolonged contact in household-type setting during 7 days before illness onset 8

Haemophilus influenzae Type B

For household contacts when infection is type b strain 8:

• Confirm all children aged up to 10 years have received Hib vaccination 8
• Rifampicin 20 mg/kg once daily (maximum 600 mg) for 4 days for adults and children >3 months in at-risk households 8
• Infants <3 months: 10 mg/kg once daily for 4 days 8

Pneumococcal Meningitis

Close contacts are not usually at increased risk 8:

• Antibiotic prophylaxis not indicated 8
• Discuss clusters in elderly care homes with local health protection authority 8

Vaccination

• Pneumococcal vaccine recommended after pneumococcal meningitis and for persons with CSF leakage 4
• Patients with complement deficiency or on Eculizumab should be vaccinated against meningococcus 8

Recurrent Meningitis Evaluation

Immunological investigations indicated for 8:

• Two or more episodes of meningococcal or pneumococcal meningitis 8
• Family history of more than one episode of meningococcal disease 8
• Single episode does NOT require immunological screening unless other indication present 8

Investigate for CSF leak in patients with 8:

• History of trauma or recent neurosurgery 8
• Evidence of rhinorrhea or otorrhea 8

Common Pitfalls to Avoid

Critical errors that worsen outcomes 4, 3:

• Relying on the classic triad for diagnosis - present in <50% of cases 4, 3
• Delaying antibiotic treatment - must start within 1 hour 4
• Failing to recognize atypical presentations in elderly patients - higher mortality risk 4
• Overlooking the need for ampicillin in adults >50 years - essential for Listeria coverage 4
• Neglecting to assess for hearing loss and other sequelae before discharge 4
• Assuming patients can immediately return to normal activities - fatigue and other symptoms often persist weeks to months 3