What are the signs of meningeal (meninges) involvement?

From the Guidelines

Meningeal signs, such as nuchal rigidity, Kernig's sign, and Brudzinski's sign, should not be relied upon for diagnosis, as they may be absent in certain patients or have limited diagnostic accuracy, and instead, prompt medical evaluation, including lumbar puncture, is essential to rule out life-threatening conditions requiring immediate treatment. The three classic meningeal signs are nuchal rigidity (neck stiffness), Kernig's sign, and Brudzinski's sign, which occur due to inflammation of the meninges causing irritation of the nerve roots, leading to protective muscle spasms when stretched 1. Additional signs may include photophobia, phonophobia, and altered mental status. It's essential to note that meningeal signs may be absent in very young or elderly patients, immunocompromised individuals, or early in the disease process.

Diagnostic Approach

When meningeal signs are present, a thorough diagnostic work-up is necessary, including:

• Documentation of presence or absence of headache, altered mental status, neck stiffness, fever, rash, seizures, and signs of shock 1
• Lumbar puncture to analyze cerebrospinal fluid (CSF) for white blood cell count, protein, glucose, and culture, which remains the principal contributor to the final diagnosis 1
• Cranial imaging may be considered to evaluate for signs of brain shift as a precaution in selected patients before lumbar puncture, but should not delay antibiotic treatment 1

Importance of Prompt Evaluation

Prompt medical evaluation is crucial, as delays in treatment can lead to increased morbidity and mortality. The UK Joint Specialist Societies guideline recommends rapid admission to hospital and consideration of a lumbar puncture for patients with suspected meningitis and/or meningococcal sepsis 1. The ESCMID guideline advises to strive for treatment of all patients with suspected bacterial meningitis within one hour, irrespective of cranial imaging before the lumbar puncture 1.

CSF Analysis

CSF analysis is essential for the diagnosis of meningitis, and the gold standard for the diagnosis of bacterial meningitis is CSF culture, which is diagnostic in 70-85% of cases of bacterial meningitis 1. Even if rendered culture negative, CSF analysis may be helpful up to 48 hours after commencing parenteral antibiotics. The CSF white blood cell count, protein, glucose, and culture results can help differentiate between bacterial, viral, tuberculous, and fungal meningitis 1.

From the Research

Meninges Signs

• The diagnosis of meningitis is often aided by clinical signs such as nuchal rigidity, Kernig's sign, and Brudzinski's sign 2.
• These signs rely on the principle that stretching the inflamed meningeal membranes causes clinically detectable irritation 2.
• The presence of positive meningitic signs increases the likelihood of a diagnosis of meningitis, while the absence of these signs reduces this probability 2.
• The utility of these signs is greatest when combined with other features in the history and examination to contribute to a comprehensive clinical assessment 2.

Lumbar Puncture and CT Scan

• A lumbar puncture (LP) is often essential for the diagnosis of bacterial meningitis, but it can worsen brain displacement in case of a space-occupying lesion 3.
• A CT scan of the brain is sometimes performed prior to LP to identify potential contraindications, but this can delay empirical treatment with antibiotics 3, 4.
• The level of agreement between experts in diagnosing a contraindication for LP on CT scan is low 3.
• Current international guidelines recommend cerebral computerized tomography (CT) before LP in many adults with suspected acute bacterial meningitis (ABM), but this may contribute to an avoidable delay of LP and ABM treatment 4.

Guidelines for CT Prior to Lumbar Puncture

• Different international guidelines (e.g. IDSA, UK, ESCMID, Swedish) have varying recommendations for cranial imaging before LP in adults with suspected meningitis 5, 6.
• These guidelines have different sensitivities for recommending neuroimaging in cases with brain shift on CT, and may recommend imaging in a varying percentage of cases 5, 6.
• The IDSA guidelines are the most sensitive, but also recommend the most CT studies with normal findings and incidental or spurious CT findings 5, 6.
• The UK and ESCMID guidelines are more selective and limit the number of normal studies and incidental or spurious CT findings 5.