Infectious meningitis and encephalitis: A primer for acute care practitioners

Meningitis and encephalitis affect all ages, are prone to misdiagnosis and outcome can be devastating. We provide this common primer for all in the sepsis "chain-of-survival." Meningitis equals inflammation/infection of the protective membranes that cover the brain; whereas encephalitis affects the brain parenchyma. Meningitis is more common, but they can co-exist as meningoencephalitis. Encephalitis can also affect the spinal cord (encephalomyelitis). Worldwide, meningitis affects 2.5 million people annually, and kills over 200,000. Central nervous system (CNS) infections account for 3.9% of all UK intensive care unit (ICU) infections, and 0.7% of adult ICU admissions. While this means these are not common causes for admission, they do have high morbidity and mortality. The median ICU stay is 4 days, of which 3 days was the median spent requiring advanced respiratory support or support for more than one organ. The median in-hospital stay is 20 days. Most admissions come through the emergency department (ED). Signs and symptoms can be vague and varied; hence potential misdiagnosis as flu, psychiatric disorders, intoxication, even hangover. The median time between hospital admission and transfer to ICU is 1 day, and by this time approximately one-third are comatose and one-sixth need respiratory support. The risk of misdiagnosis matters given high mortality and morbidity: 18%-25% die in hospital and 1-in-10 survivors lose independence. During the past 20 years mortality has fallen, but those left with some form of permanent disability remains constant at nearly 40%. Fortunately, early recognition and treatment can greatly improve outcome. Regarding diagnosis, history and physical examination still have great value. Next, lumbar puncture (LP) should be expedited unless contraindicated by coagulopathy, skin infection, or raised ICP. LP testing should incorporate opening pressure, microscopy, culture and cell count, glucose and protein and often polymerase chain reaction (PCR) for meningococcus, pneumococcus, herpes simplex virus (HSV1&2), varicella (VZV) and enterovirus. Radiologically, head computed tomography (CT) is first line. It may reduce the risk of LP by excluding pathologies likely to trigger herniation. CT is indicated if their Glasgow Coma Score (GCS) is falling or ⩽9, or if seizures, focal neurological signs or papilloedema. Normal CT cannot rule out raised ICP, but LP is avoided if the CT shows herniation, basal cistern or foramen magnum effacement, cerebral swelling, intracranial lesions/collections with mass effect or obstructive hydrocephalus. Magnetic resonance imaging (MRI) is logistically tougher but better at detecting meningitis/encephalitis. MRI can suggest the causative organisms, along with complications such as infarct, pus and parenchymal changes. Treatment centres on prompt antimicrobials: usually a third-generation intravenous (IV) cephalosporin, typically within 1 h, and at an increased (i.e. "meningitis") dose. Intravenous amoxicillin is added in the elderly or immunocompromised, plus aciclovir if viral encephalitis is plausible. Treatment delays (over 4 h) are associated with increased mortality. Over half (57%) of patients that require ICU develop intracranial complications, most frequently ischaemia, cerebral oedema and ventriculitis. In short, these diseases are life-threatening but manageable if we do the simple stuff right. . .and right away.