Infectious Disease · Central Nervous System Infections
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The classic triad of fever, nuchal rigidity, and altered mental status is present in less than half of adult patients, making a high index of suspicion mandatory.
Lumbar puncture is the diagnostic gold standard, revealing elevated opening pressure, high protein, low glucose, and neutrophilic pleocytosis.
Empiric antibiotic therapy with vancomycin and a third-generation cephalosporin (ceftriaxone or cefotaxime) must be initiated immediately upon suspicion, even before diagnostic confirmation.
Dexamethasone should be administered with or just before the first dose of antibiotics to reduce neurological sequelae and hearing loss, particularly in cases of Streptococcus pneumoniae.
Head CT must be performed prior to lumbar puncture only in patients with focal neurological deficits, new-onset seizures, papilledema, or immunocompromised state to rule out mass effect.
Neisseria meningitidis is the most common cause in adolescents and young adults and is classically associated with a petechial or purpuric rash.
Listeria monocytogenes is a critical consideration in patients over 50, the immunocompromised, or neonates, necessitating the addition of ampicillin to the standard empiric regimen.
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A 24-year-old college student is brought to the emergency department by his roommate due to a 12-hour history of high fever, severe headache, and confusion. Physical examination reveals a stiff neck and a non-blanching petechial rash on the lower extremities. The patient is hemodynamically stable with no focal neurological deficits. A lumbar puncture is performed, showing a white blood cell count of 2,500/mm³ with 90% neutrophils, protein of 150 mg/dL, and glucose of 30 mg/dL.
What is the most appropriate next step in management for this patient?
Initiation of intravenous vancomycin, ceftriaxone, and dexamethasone.
The patient presents with classic signs of bacterial meningitis; the prompt requires immediate empiric coverage with antibiotics and adjunctive steroids to prevent complications, as per the 'bets' regarding empiric therapy and dexamethasone.
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Etiology / Epidemiology
S. pneumoniae is the most common cause in adults; N. meningitidis is common in adolescents/dorms.
Clinical Manifestations
Classic triad: fever, nuchal rigidity, and altered mental status. Look for Kernig and Brudzinski signs.
Diagnosis
Lumbar puncture is the gold standard; CSF shows low glucose, high protein, and high neutrophils.
Treatment
Empiric 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
Adults are primarily affected by S. pneumoniae. Adolescents and young adults in close quarters are at risk for N. meningitidis. Neonates are typically infected by Group B Streptococcus or Listeria monocytogenes.
Pertinent Anatomy
The infection involves the leptomeninges (arachnoid and pia mater). Inflammation leads to increased intracranial pressure and potential herniation.
Pathophysiology
Bacteria colonize the nasopharynx, invade the bloodstream, and cross the blood-brain barrier. This triggers a massive inflammatory response in the subarachnoid space, causing cerebral edema and impaired CSF outflow.
Clinical Manifestations
Patients present with the classic triad of fever, nuchal rigidity, and altered mental status. Physical exam reveals Kernig sign (pain with knee extension) and Brudzinski sign (neck flexion causes hip flexion). Petechial rash is highly suggestive of N. meningitidis.
Diagnosis
Lumbar puncture is the gold standard. CSF analysis typically shows glucose <40 mg/dL, protein >200 mg/dL, and neutrophilic pleocytosis. CT head must be performed prior to LP if there is evidence of papilledema, focal neuro deficits, or immunocompromise to rule out mass effect.
Treatment
Initiate empiric ceftriaxone and vancomycin immediately. Add dexamethasone prior to or with the first dose of antibiotics to decrease inflammation. Dexamethasone is specifically indicated for suspected pneumococcal meningitis. If Listeria is suspected (age >50 or immunocompromised), add ampicillin.
Prognosis
Early recognition is critical to prevent permanent neurological deficits. Sensorineural hearing loss is the most frequent complication. Survivors may experience cognitive impairment or seizure disorders.
Differential Diagnosis
Viral meningitis: CSF shows normal glucose and lymphocytic pleocytosis
Fungal meningitis: CSF shows very low glucose and elevated opening pressure
Subarachnoid hemorrhage: Sudden onset 'thunderclap' headache with xanthochromia on LP
Brain abscess: Focal neurological deficits with ring-enhancing lesion on CT
Encephalitis: Altered mental status with prominent personality changes or seizures