What is aseptic meningitis?

What is Aseptic Meningitis?

Aseptic meningitis is a syndrome characterized by acute onset of meningeal symptoms (neck stiffness, headache, photophobia), fever, and cerebrospinal fluid pleocytosis with bacteriologically sterile cultures—meaning no bacterial or fungal organisms are identified. 1

Definition and Core Characteristics

Aseptic meningitis represents meningeal inflammation with CSF pleocytosis (≥5 cells/mm³) that is not caused by bacterial infection. The term encompasses multiple etiologies, though viral infections account for the majority of cases, with enteroviruses being the most common culprit 2, 1.

Key Clinical Features

Patients typically present with:

• Neck stiffness, headache, and photophobia (classic meningism triad)
• Fever (though not always present)
• Preserved consciousness level in adults—any alteration suggests alternative diagnoses like bacterial meningitis, encephalitis, or other intracranial pathology 2
• Non-specific symptoms: diarrhea, vomiting, muscle pain, sore throat 2

Critical distinction: Unlike bacterial meningitis, patients with aseptic meningitis typically do not have reduced consciousness. If mental status is altered, you must consider bacterial meningitis, encephalitis, subarachnoid hemorrhage, or space-occupying lesions 2.

Epidemiology and Common Causes

Viral meningitis accounts for 50-80% of all meningitis cases, though precise incidence is unknown due to underreporting 2. In the UK, the most common viral causes are:

Primary Viral Etiologies:

• Enteroviruses (>90 serotypes; transmitted fecal-oral route)—most common overall 2
• HSV-2 (sexually transmitted; can occur with primary infection or reactivation)
• VZV (respiratory transmission; may occur with or without rash)
• Less common: CMV, EBV, mumps virus 2

Important clinical pearls:

• HSV-2 meningitis rarely presents with concurrent genital ulcers 2
• VZV meningitis can occur without chickenpox or shingles rash 2
• HSV-1 more commonly causes encephalitis than meningitis 2

Non-Viral Causes (True Aseptic Meningitis):

Three main categories 3:

1. Systemic diseases with meningeal involvement: Sarcoidosis, Behçet's disease, Sjögren's syndrome, SLE, granulomatosis with polyangiitis

2. Drug-induced: NSAIDs, antibiotics (sulfamides, penicillins, amoxicillin), IVIG, monoclonal antibodies 3, 4

3. Neoplastic meningitis: Solid cancer metastases (breast, lung, melanoma) or hematologic malignancies (lymphoma, leukemia)

Diagnostic Approach

CSF Analysis Requirements

When viral meningitis is suspected, CSF should be tested for 2:

• Enteroviruses by PCR
• HSV-1 and HSV-2 by PCR
• VZV by PCR
• Additional viral PCR or serology guided by clinical features (immunocompromise, travel history)
• Stool and/or throat swabs for enterovirus PCR

Typical CSF findings 4, 5:

• Leukocytosis (100% of cases)
• Lymphocytic predominance (63.6% of cases)
• Elevated protein (90%)
• Normal glucose (95.5%)
• Negative bacterial culture (100%)

Critical caveat: Despite advanced diagnostics including PCR and next-generation sequencing, 30-50% of presumed viral meningitis cases remain without identified pathogen 2, 3.

Management Strategy

Treatment Principles

There are currently no treatments of proven benefit for most causes of viral meningitis 2. Management is primarily supportive:

• Analgesia and fluids as needed
• Stop antibiotics once viral diagnosis is confirmed 2
• Do NOT give aciclovir/valaciclovir for HSV or VZV meningitis—no evidence supports this, and risks from drug side effects and prolonged hospitalization outweigh unproven benefits 2

When to Suspect Non-Viral Aseptic Meningitis

Consider drug-induced causes if:

• Recent medication initiation (NSAIDs, antibiotics, biologics)
• Recurrent episodes (95.5% of amoxicillin-induced cases are recurrent) 4
• Symptoms resolve within 1-4 days of drug discontinuation 4

Prognosis and Follow-Up

Although rarely fatal in immunocompetent adults, aseptic meningitis can cause significant morbidity 2:

Common Post-Discharge Issues:

• Fatigue and sleep disorders
• Emotional difficulties and psychological impacts
• Headaches (up to one-third of patients)
• Arthritis, limb pain, neuropathic pain 2

Critical management point: Many patients feel well at discharge but cannot immediately return to normal activities. Staged return to work/studies on part-time basis initially is recommended 2.

Follow-Up Recommendations:

• Post-hospital follow-up should be offered to all patients with confirmed or probable meningitis 2
• Early referral to mental health services if needed 2
• Support from organizations like Meningitis Research Foundation or Meningitis Now 2

Common Pitfalls to Avoid

1. Do not assume altered consciousness is compatible with viral meningitis—this mandates evaluation for bacterial meningitis or encephalitis 2

2. Do not treat presumed viral meningitis with aciclovir prophylactically—no evidence supports this practice 2

3. Do not discharge without counseling about expected recovery trajectory—fatigue and cognitive issues may persist for weeks to months 2

4. Do not overlook medication history—drug-induced aseptic meningitis is underrecognized and resolves with discontinuation 3, 4