What is the diagnostic workup for meningitis?

From the Guidelines

A meningitis workup should begin with blood tests, including culture, pneumococcal and meningococcal PCR, glucose measurement, lactate measurement, and procalcitonin, followed by a lumbar puncture to obtain cerebrospinal fluid (CSF) for analysis, as recommended by the UK Joint Specialist Societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults 1. The initial blood tests are crucial in identifying the cause of meningitis and guiding empiric antimicrobial therapy.

• The blood culture should be taken prior to antibiotics wherever possible, and if antibiotics have been given in the community, blood cultures should be taken as soon as possible on arrival in hospital, within the first hour 1.
• Pneumococcal and meningococcal PCR should also be performed on an EDTA sample 1.
• Additionally, glucose measurement, lactate measurement, and procalcitonin (if available) should be included in the initial blood tests 1. The lumbar puncture should be performed to obtain CSF for analysis, including cell count, glucose, protein, Gram stain, culture, and potentially PCR testing.
• The CSF opening pressure should be documented, unless the LP is performed in the sitting position 1.
• CSF glucose with concurrent plasma glucose, CSF protein, and other relevant tests should also be performed 1. While awaiting results, empiric antimicrobial therapy should be initiated immediately after obtaining blood cultures.
• For adults with suspected bacterial meningitis, the choice of antibiotics needs to be differentiated according to the patient's age, risk factors, and local resistance rates of pneumococci, as advised by the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) guideline 1.
• Dexamethasone is the only proven adjunctive treatment and should be started together with the antibiotics, as recommended by the ESCMID guideline 1. Neuroimaging (CT or MRI) should be performed before lumbar puncture if there are focal neurological deficits, new seizures, papilledema, immunocompromise, or altered consciousness to rule out increased intracranial pressure or mass lesions, as recommended by the Practice Guidelines for Bacterial Meningitis 1.
• The empiric regimen should be adjusted based on CSF results, patient age, immune status, and local resistance patterns.
• Therapy duration typically ranges from 7-21 days depending on the identified pathogen. Rapid diagnosis and treatment are critical as bacterial meningitis can progress quickly and lead to permanent neurological damage or death if not promptly addressed.

From the Research

Meningitis Workup

• The diagnosis of bacterial meningitis can be challenging, as patients often lack some of the characteristic findings of this disease with presentations that overlap with more common disorders seen in the emergency department 2.
• Physical examination may not perform well enough to accurately identify patients with meningitis, and traditionally described lumbar puncture results for viral and bacterial disease cannot always predict bacterial meningitis 3.
• Central nervous system (CNS) imaging and lumbar puncture (LP) may be needed to further evaluate for these diagnoses 2.

Diagnostic Considerations

• Common symptoms of herpes simplex virus type 2 (HSV-2) meningitis include headache, photophobia or phonophobia, and neck stiffness 4.
• The median time to lumbar puncture was 2.0 hours, and the median cerebrospinal fluid (CSF) leukocyte count was 360 × 10^6/L, with a mononuclear predominance of 97% 4.
• Lumbar puncture was preceded by brain imaging in 30% of patients with HSV-2 meningitis 4.

Imaging and Lumbar Puncture

• The utility of obtaining head computed tomography (CT) prior to lumbar puncture in adults with suspected bacterial meningitis is unclear, with some studies suggesting that it may not decrease the risk of brainstem herniation 5.
• Decision rules to selectively perform CT on only those individuals most likely to have intracranial mass effect lesions have not undergone validation 5.
• Physicians should consider selective CT for those patients at risk for intracranial mass effect lesions based on decision rules or clinical gestalt 5.

Management and Treatment

• The timely diagnosis and administration of appropriate antibiotic therapy are pivotal elements in managing bacterial meningitis 6.
• Current national guidelines recommend that all patients presenting with suspected bacterial meningitis receive antibiotics within one hour 6.
• Steroids should be administered to patients suspected of having bacterial meningitis, excluding those displaying signs of meningococcal sepsis, such as a rash 6.