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INTRODUCTION

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Identifying infections in the central nervous system (CNS) can be challenging for clinicians in the Emergency Department (ED), as invasive testing is often required for definitive diagnoses. Bacterial meningitis, viral encephalitis, brain abscess, and spinal epidural abscess are life-threatening emergencies that can initially present with a spectrum of nonspecific symptoms that may make early diagnosis difficult. Differentiating these conditions from viral meningitis or other conditions that can be treated with supportive care is important when a CNS infection is suspected.

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MENINGITIS AND ENCEPHALITIS

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Clinical Features

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Meningitis is inflammation of the membranes surrounding the brain and spinal cord. Bacterial meningitis is inflammation caused by infection, often with encapsulated organisms, and is a life-threatening emergency. Even with appropriate and timely treatment this emergent CNS infection can have significant morbidity and mortality. Aseptic meningitis is diagnosed when such inflammation is due to causes other than bacterial infection, such as drug reactions, rheumatologic conditions, or nonbacterial infections such as fungi or viruses. Enteroviruses and echoviruses are the most common causes of aseptic meningitis.

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The classically described clinical triad of meningitis is fever, neck stiffness, and altered mental status, although less than half of patients will initially present with all three of these features. Headache is a common symptom and fever is often present. Many initial symptoms such as headache, fever, neck pain, nausea, and vomiting are nonspecific and overlap with other more common conditions, which can make early diagnosis a challenge especially in very young and very old patients.

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Physical findings often include fever, and when CNS infection is suspected clinicians should evaluate for the presence of meningeal signs such as nuchal rigidity (severe neck stiffness), Kernig's sign (pain in the back and legs with flexing the hip and extending the knee), and Brudzinski's sign (flexion of the hips with passive flexion of the neck), although these classically described findings have been demonstrated to have poor sensitivity for meningitis. Evaluate mental status and look for potential neurological deficits that may accompany CNS infections such as cranial nerve palsies or other focal findings. Examine the skin for petechiae, splinter hemorrhages, or other findings concerning for systemic infection.

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Encephalitis is an infection of the brain parenchyma that causes inflammation within the CNS and is often caused by viral infection. This can be caused by a number of different viral pathogens including herpes simplex virus (HSV), which is the most treatable cause of encephalitis. Patients with acute viral encephalitis will present with many of the same signs and symptoms as bacterial meningitis, such as fever, stiff neck, or headache. Additionally, patients diagnosed with encephalitis typically present with altered mental status, cognitive deficits, psychiatric symptoms, or seizures.

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Diagnosis and Differential

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A promptly performed lumbar puncture (LP) to obtain cerebrospinal fluid (CSF) is the appropriate diagnostic procedure for patients with suspected meningitis or encephalitis. ...

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