Meningitis

Meningitis refers to leptomeningeal enhancement, although it is often used for a specific subset of meningitis: acute, bacterial meningitis. See Meninges for a detailed review of the meningeal layers and spaces.

• Headache
• Photophobia
• Nausea/Vomiting
• Altered mental status (especially, confusion and depressed level of consciousness)
• Seizure

• Without going into a detailed differential diagnosis, it's helpful to consider that migraine and subarachnoid hemorrhage have similar symptom patterns. So, when we think of those diagnoses, we should also be thinking about bacterial meningitis (albeit far less common).

• Fever
• Focal neurological deficits (we can think of one-third of patients as having these).
• Meningismus. Two notable physical exam signs for meningismus (maneuvers that exacerbate meningismus):
• Kernig sign, which is positive if the patient has their hip flexed to 90 degrees but cannot fully extend the knee.
• Brudzinski sign is positive if with passive neck flexion, the patient automatically flexes the hip and knee.
• Rash occurs in meningococcal meningitis in roughly 60% of cases.

Basic diagnostic testing in suspected bacterial meningitis:

• All patients should be sent for a STAT noncontrast head CT to look for other culprits (eg subarachnoid hemorrhage) and to look for signs of increased intracranial pressure (ICP).
• Lumbar puncture for CSF evaluation (if no red flag features of ICP).
• Blood cultures.
• Note that blood cultures should be done prior to administering antibiotic therapy but antibiotics should not be delayed for lumbar puncture.
• Although blood cultures are not as reliable as CSF cultures for meningitis management, there are instances where LP cannot be performed.
• It is important to know when it is unsafe to perform a lumbar puncture due to the risk of brain herniation.

Brain herniation from lumbar puncture is a concern in the clinical setting of:

• Reduced level of consciousness
• Focal neurological deficits
• Papilledema.
• CT findings of increased intracranial pressure such as:
• Obliteration of CSF spaces, meaning compression (effacement) of the ventricles and obliteration of the cisterns and sulcal spaces.
• Loss of grey/white differentiation of the cerebral gyri.
• Signs of brain herniation

CSF pathologic changes help us distinguish key forms of meningitis.

• CSF normally contains less than 10 cells, 70% of which are lymphocytes, that glucose is 60% of that of the serum glucose, protein is from 15 to 45, and CSF pressure is usually 70 to 180 mmH2O.
• In bacterial meningitis, there is > 100 cells, typically greater than a 1,000. The majority are polymorphonuclear cells, the glucose is low, protein is elevated (> 50) (as it is in viral and granulomatous), pressure is elevated from CSF ventricular obstruction.

Viral & Fungal (Granulomatous)

• In viral meningitis, cell counts are typically from 50 to 250 (as in granulomatous), the majority of cells are usually lymphocytes (as in granulomatous), glucose is often normal – this is a key distinguisher from granulomatous; in granulomatous meningitis, glucose is low, like it is in bacterial.
• In viral meningitis pressure is often normal; whereas in granulomatous its variable, depending on the degree of CSF obstruction.

Note that the blood-brain barrier reduces penetration of the antibiotics so higher doses of medication are required to treat meningitis than other systemic infections. Adult dose: 10 mg Q 6 hours IV (for 4 days) Pediatric dose: 0.15 mg/kg IV (for 2 - 4 days) Adult dose: Ceftriaxone 2 grams Q 12 hours IV Pediatric dose: Ceftriaxone 50mg/kg Q 12 hours IV Adult dose: Vancomycin 1 gram Q 12 hours IV Pediatric dose: Vancomycin 15 mg/kg Q 6 hours IV Adult dose: Ampicillin 2 g Q 4 hours IV Pediatric dose: Ampicillin 75 mg/kg Q 6 hours IV Adult dose: Acyclovir 10 mg/kg Q 8 hours IV Pediatric dose: Acyclovir 10-20 mg/kg Q 8 hours IV Newborns receive a different regimen, which we will not include in detail. For reference, it is typically recommended they receive a combination of vancomycin, an aminoglycoside, and cefepime or meropenem. 19 year-old-male with acute-onset of confusion. 23 year-old woman presents with a rapidly progressive stupor.