USMLE Step 1 Meningitis practice questions
Meningitis is inflammation of the meninges, most often caused by bacterial, viral, or fungal pathogens that gain access to the subarachnoid space via hematogenous spread, contiguous spread, or direct inoculation. For USMLE Step 1, focus on the basic science: which organisms predominate at each age and immune status, how CSF glucose/protein/cell counts reflect underlying pathophysiology, and the molecular mechanisms of complications such as DIC, adrenal hemorrhage, and impaired CSF resorption. Step 1 tests mechanism and diagnosis, not antibiotic choice or dosing.
A 12-day-old male infant, born at term via uncomplicated vaginal delivery, is brought to the emergency department because, as his mother states, "he won't stop crying and won't eat." Symptoms have progressed over 12 hours. Temperature is 38.9°C (102°F). Examination shows a bulging anterior fontanelle and diffuse hypotonia. Lumbar puncture yields cloudy cerebrospinal fluid with a neutrophilic pleocytosis. Which of the following organisms is the most likely cause of this infant's condition?
A 4-year-old unvaccinated boy is brought to the emergency department for fever, neck stiffness, and lethargy that began 8 hours ago. His mother reports, "He was fine yesterday, and now he can't stand the light." Temperature is 39.4°C (103°F). Kernig sign is positive. Lumbar puncture shows an opening pressure of 320 mm H2O, WBC count of 5,200/mm³ with 90% neutrophils, protein of 210 mg/dL, and glucose of 28 mg/dL (serum glucose 95 mg/dL). Which of the following processes is most directly responsible for this patient's cerebrospinal fluid glucose concentration?
An 18-year-old man living in a college dormitory is brought to the emergency department for fever, headache, and a rapidly spreading purpuric rash of 6 hours' duration. He tells the physician, "I feel like I'm going to pass out." Temperature is 39.8°C (103.6°F), blood pressure is 78/42 mm Hg, and pulse is 140/min. Examination reveals diffuse petechiae and purpura over the trunk and extremities. Blood cultures grow gram-negative diplococci. Over the following hours he develops signs of acute adrenal insufficiency. Which of the following is the most likely mechanism underlying this patient's hypotension and adrenal findings?
A 22-year-old woman comes to the office after her third episode of Neisseria meningitidis bacteremia over the past 4 years, each successfully treated with antibiotics. She has not undergone splenectomy and takes no immunosuppressive medications. Her brother has had a similar history of recurrent meningococcal infections. Which of the following is the most likely underlying cause of this patient's susceptibility to recurrent infection?
A 38-year-old man with HIV infection (CD4+ count 42/mm³), not currently on antiretroviral therapy, comes to the emergency department for a 3-week history of gradually worsening headache and confusion. He says, "The headache won't go away no matter what I take." Temperature is 37.6°C (99.7°F), and nuchal rigidity is mild. Lumbar puncture shows an opening pressure of 350 mm H2O. India ink staining of the cerebrospinal fluid reveals encapsulated budding yeast. Which of the following properties of the causative organism is most directly responsible for this patient's elevated opening pressure?
Meningitis, answered
How do I quickly differentiate bacterial from viral meningitis on CSF analysis for Step 1?
Bacterial meningitis classically shows a neutrophilic pleocytosis, high protein, and low glucose because bacteria and neutrophils consume glucose. Viral meningitis typically shows a lymphocytic pleocytosis, mildly elevated or normal protein, and normal glucose, since viral replication does not deplete CSF glucose the way bacterial metabolism does.
Do I need to memorize specific antibiotic regimens for meningitis for Step 1?
No. Step 1 emphasizes mechanisms, causative organisms by age or risk group, and pathophysiology of complications rather than specific drug choice, dosing, or empiric antibiotic algorithms; that management-level detail is tested on Step 2 CK.
What is the single most important age-based fact to know about meningitis pathogens?
Know how the most likely organism shifts with age: Group B Streptococcus and E. coli in neonates, Streptococcus pneumoniae and Neisseria meningitidis in children and young adults, and Streptococcus pneumoniae and Listeria monocytogenes in older or immunocompromised adults.
How is meningitis distinguished from encephalitis on Step 1 vignettes?
Meningitis presents primarily with meningeal signs such as headache, fever, nuchal rigidity, and photophobia, with a normal level of consciousness aside from lethargy. Encephalitis involves the brain parenchyma itself, so vignettes emphasize altered mental status, focal neurologic deficits, or seizures, often pointing toward a viral cause such as herpes simplex virus.
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