Infectious Disease · Central Nervous System Infections
The facts most likely to be tested
The classic triad of fever, nuchal rigidity, and altered mental status is present in less than half of adult patients with bacterial meningitis.
Perform a lumbar puncture immediately in patients with suspected meningitis unless there are signs of increased intracranial pressure or focal neurologic deficits requiring a head CT first.
Empiric treatment for community-acquired bacterial meningitis in adults is vancomycin plus a third-generation cephalosporin (ceftriaxone or cefotaxime).
Add dexamethasone to the initial antibiotic regimen to reduce neurologic sequelae and mortality in cases of suspected *Streptococcus pneumoniae* meningitis.
Add ampicillin to the empiric regimen for patients over age 50 or those who are immunocompromised to provide coverage for *Listeria monocytogenes*.
Cerebrospinal fluid analysis showing elevated opening pressure, high protein, low glucose, and neutrophilic pleocytosis is diagnostic for bacterial meningitis.
Post-exposure prophylaxis with rifampin, ciprofloxacin, or ceftriaxone is indicated for close contacts of patients with *Neisseria meningitidis*.
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A 55-year-old male is brought to the emergency department by his wife due to a 24-hour history of high fever, severe headache, and confusion. On physical examination, the patient is febrile at 102.4°F and exhibits nuchal rigidity and a positive Kernig sign. He has no history of recent travel or trauma, but he is currently undergoing chemotherapy for non-Hodgkin lymphoma. A non-contrast head CT is performed and shows no evidence of mass effect or midline shift.
What is the most appropriate empiric antibiotic regimen for this patient?
Vancomycin, ceftriaxone, and ampicillin
The patient is immunocompromised, necessitating the addition of ampicillin to the standard vancomycin and ceftriaxone regimen to cover for Listeria monocytogenes.
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Etiology / Epidemiology
Streptococcus pneumoniae is the most common cause in adults; Neisseria meningitidis is common in adolescents/dorms.
Clinical Manifestations
Classic triad: fever, nuchal rigidity, and altered mental status; Kernig sign and Brudzinski sign.
Diagnosis
Lumbar puncture is the gold standard; CSF glucose <40 mg/dL and protein >100 mg/dL suggest bacterial.
Treatment
Ceftriaxone plus Vancomycin; add Dexamethasone to reduce neurological sequelae.
Prognosis
High mortality if untreated; sensorineural hearing loss is the most common long-term complication.
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Epidemiology & Etiology
Bacterial meningitis is a medical emergency requiring rapid identification of S. pneumoniae, N. meningitidis, or Listeria monocytogenes. Listeria is a critical consideration in patients >50, neonates, and the immunocompromised. Outbreaks of N. meningitidis are associated with crowded living conditions like college dorms or military barracks.
Pertinent Anatomy
The subarachnoid space contains the cerebrospinal fluid (CSF) and major cerebral vessels. Inflammation of the leptomeninges (arachnoid and pia mater) leads to increased intracranial pressure and potential herniation.
Pathophysiology
Pathogens typically reach the meninges via hematogenous spread or direct extension from sinus/ear infections. Bacterial toxins trigger an intense inflammatory response, increasing blood-brain barrier permeability and causing cerebral edema. This leads to elevated intracranial pressure (ICP) and potential cranial nerve palsies.
Clinical Manifestations
Patients present with the classic triad of fever, nuchal rigidity, and altered mental status. Look for Kernig sign (pain with knee extension) and Brudzinski sign (neck flexion causes hip flexion). Papilledema or focal neurological deficits are red flags for mass effect, necessitating a CT scan before lumbar puncture.
Diagnosis
Perform Lumbar puncture for CSF analysis; if focal deficits exist, obtain CT head first to rule out herniation risk. Bacterial CSF shows elevated opening pressure, neutrophilic pleocytosis, low glucose (<40 mg/dL), and high protein (>100 mg/dL). Gram stain and culture are essential for definitive pathogen identification.
Treatment
Initiate empiric Ceftriaxone and Vancomycin immediately after blood cultures. Add Ampicillin if Listeria is suspected (age >50 or immunocompromised). Administer Dexamethasone prior to or with the first dose of antibiotics to decrease inflammation. Do not delay antibiotics for imaging if the patient is stable.
Prognosis
Early recognition is vital to prevent permanent neurological deficits. Sensorineural hearing loss is the most common sequela, particularly with *S. pneumoniae*. Monitor for seizures and increased ICP during the acute phase.
Differential Diagnosis
Viral meningitis: CSF shows lymphocytic pleocytosis and normal glucose
Subarachnoid hemorrhage: Sudden 'thunderclap' headache and xanthochromia on CSF
Brain abscess: Focal neurological deficits and ring-enhancing lesion on CT
Encephalitis: Altered mental status and personality changes with normal CSF glucose
Fungal meningitis: Chronic presentation with low glucose in immunocompromised patients