All questions
Question 1
A 33-year-old woman reports 2 episodes of neurologic symptoms over 8 months. The first was painful vision loss in the left eye that improved over weeks. The second is 5 days of numbness and tingling in both legs with unsteady gait. She has fatigue and heat sensitivity. No fever. Exam shows decreased visual acuity in the left eye with a relative afferent pupillary defect, mild spasticity in both legs, hyperreflexia, and an upgoing plantar response on the right. Sensation to vibration is reduced in the feet. CBC and CMP are normal. MRI brain shows multiple ovoid periventricular T2 hyperintense lesions; one lesion enhances with gadolinium. A lumbar puncture is performed to support the suspected diagnosis and guide counseling about disease-modifying therapy.
- Neutrophilic pleocytosis with low CSF glucose
- Oligoclonal IgG bands with elevated IgG index (correct answer)
- Markedly elevated CSF opening pressure
- Xanthochromia with persistent RBCs
- Eosinophils with very high CSF protein
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes recurrent neurologic episodes with MRI lesions, guiding the choice of lumbar puncture. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing evidence of intrathecal IgG synthesis supportive of multiple sclerosis. Choice A is incorrect due to suggesting bacterial infection, which often results from confusing inflammatory patterns. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 2
A 30-year-old woman presents with 1 day of fever, headache, photophobia, and confusion. She had a generalized tonic-clonic seizure in the ED. Exam shows disorientation and a subtle right arm pronator drift. T 39.0°C. Because she has a new seizure and focal neurologic deficit, the team obtains neuroimaging before lumbar puncture. Which neuroimaging modality is most appropriate for the initial evaluation to assess for mass effect or hemorrhage quickly?
- Noncontrast CT of the head (correct answer)
- MRI brain with and without contrast
- MR angiography of the head
- CT of the cervical spine
- Transcranial Doppler ultrasonography
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, confusion, seizure, and focal signs, guiding the choice of initial neuroimaging. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing quick assessment for contraindications to lumbar puncture. Choice B is incorrect due to being time-intensive, which often results from overprioritizing detail in emergencies. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 3
A 41-year-old woman with obesity presents with daily headaches for 2 months, worse when lying down, with transient visual obscurations. She denies fever or focal deficits. Exam shows bilateral papilledema and normal motor/sensory testing. BP 128/80 mm Hg. Pregnancy test is negative. MRI brain shows no mass lesion; MR venography shows no venous sinus thrombosis. A lumbar puncture is planned to confirm suspected idiopathic intracranial hypertension and guide management. Which CSF finding is most consistent with this condition?
- Elevated opening pressure with normal CSF composition (correct answer)
- Low opening pressure with elevated protein
- Neutrophilic pleocytosis with low glucose
- Oligoclonal bands with elevated IgG index
- Xanthochromia with persistent RBCs
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes headaches and papilledema, guiding the choice of lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing confirmation of elevated pressure in idiopathic intracranial hypertension. Choice B is incorrect due to suggesting other pathologies like GBS, which often results from misattributing pressure changes. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 4
A 67-year-old man with atrial fibrillation (not on anticoagulation) develops sudden right facial droop and right arm weakness 45 minutes ago. He has difficulty speaking but follows commands. No headache or trauma. On exam, BP 158/86 mm Hg, HR 108/min irregularly irregular, glucose 112 mg/dL. Neurologic exam shows expressive aphasia and right arm drift. NIHSS is 9. The emergency team must rapidly distinguish ischemic from hemorrhagic stroke to determine eligibility for thrombolysis and possible thrombectomy. No contraindications to CT are present. The question is which neuroimaging test is most appropriate first in this setting.
- MRI brain with diffusion-weighted imaging
- Noncontrast CT of the head (correct answer)
- CT myelography
- MR venography
- PET scan of the brain
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute focal weakness and aphasia, guiding the choice of noncontrast head CT. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid exclusion of hemorrhage before thrombolysis. Choice A is incorrect due to being time-consuming in the acute window, which often results from over-relying on advanced imaging. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 5
A 40-year-old man presents with acute onset headache and fever. He is confused and has left arm weakness. CT head shows a right frontal ring-enhancing lesion with surrounding edema and mild midline shift. The team suspects a brain abscess and is considering lumbar puncture to evaluate for meningitis. Which is the most appropriate next step regarding CSF sampling in this patient?
- Avoid lumbar puncture due to herniation risk; treat and consult neurosurgery (correct answer)
- Perform lumbar puncture immediately to confirm diagnosis
- Repeat CT head after lumbar puncture
- Perform lumbar puncture after giving mannitol only
- Perform lumbar puncture only if CSF glucose is normal
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes headache, fever, and CT ring-enhancing lesion, guiding the choice of avoiding lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing risk reduction of herniation in brain abscess. Choice B is incorrect due to ignoring mass effect, which often results from underestimating imaging findings. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 6
A 46-year-old woman presents with abrupt onset severe headache that peaked within 1 minute while showering. She has photophobia and vomiting. No focal deficits. Exam shows nuchal rigidity. Vitals: BP 162/94 mm Hg, T 36.9°C. Noncontrast head CT obtained 10 hours after onset shows no hemorrhage. Lumbar puncture is performed. CSF shows: RBCs 18,000/µL in tube 1 and 17,500/µL in tube 4, protein mildly elevated, glucose normal. The sample is centrifuged. The team must interpret whether these findings support aneurysmal subarachnoid hemorrhage versus traumatic tap to determine need for urgent aneurysm evaluation.
- Clearing RBC count from tube 1 to tube 4
- Xanthochromia in centrifuged CSF supernatant (correct answer)
- Low CSF glucose with neutrophils
- Elevated CSF opening pressure alone
- Positive CSF cryptococcal antigen
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes thunderclap headache with nuchal rigidity, guiding the choice of CSF analysis. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing distinction of SAH from traumatic tap via xanthochromia. Choice A is incorrect due to indicating traumatic tap, which often results from ignoring persistent RBCs. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 7
A 19-year-old college student presents with fever, headache, and stiff neck for 12 hours. He is photophobic and vomited once. Exam shows T 39.2°C, petechial rash on the trunk, and nuchal rigidity. He is alert without focal deficits. Platelets are 180,000/µL; INR is normal. The ED plans immediate antibiotics and lumbar puncture. There is no papilledema, seizure, or focal neurologic deficit. Which is the most appropriate next step regarding neuroimaging and CSF sampling?
- Perform lumbar puncture immediately after blood cultures (correct answer)
- Obtain MRI brain before lumbar puncture
- Obtain noncontrast head CT before lumbar puncture
- Defer lumbar puncture until rash resolves
- Perform CT angiography before lumbar puncture
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, headache, rash, and no contraindications, guiding the choice of immediate lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid CSF sampling in suspected meningococcemia without delays. Choice C is incorrect due to unnecessary in low-risk cases, which often results from overapplying CT criteria. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 8
A 61-year-old man presents with sudden severe headache and neck stiffness. Noncontrast head CT is negative. Lumbar puncture is performed 2 hours after symptom onset and shows RBCs 2,000/µL in tube 1 and 200/µL in tube 4, normal glucose, and no xanthochromia. He improves with analgesics. The team must decide whether this CSF pattern is more consistent with traumatic tap or subarachnoid hemorrhage to guide further workup.
- Traumatic tap due to marked decline in RBCs across tubes (correct answer)
- Subarachnoid hemorrhage due to normal glucose
- Bacterial meningitis due to elevated RBCs
- HSV encephalitis due to absence of xanthochromia
- Multiple sclerosis due to normal opening pressure
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes sudden headache and decreasing CSF RBCs, guiding the choice of interpretation. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing distinction of traumatic tap without xanthochromia. Choice D is incorrect due to not matching the pattern, which often results from overcalling early findings. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 9
A 26-year-old woman presents with fever, headache, and neck stiffness for 4 days. She is HIV-negative and recently returned from a camping trip. Exam shows photophobia and mild confusion without focal deficits. CT head shows no mass lesion. Lumbar puncture reveals WBC 220/µL (90% lymphocytes), protein 90 mg/dL, glucose 62 mg/dL (serum 100 mg/dL). Gram stain is negative. The team suspects viral meningitis and must identify which CSF profile best fits the suspected diagnosis to avoid unnecessary broad-spectrum antibiotics.
- Lymphocytic pleocytosis with normal glucose (correct answer)
- Neutrophilic pleocytosis with very low glucose
- No WBCs with markedly elevated protein
- Eosinophilic pleocytosis with low glucose
- Xanthochromia with falling RBC count by tube
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, headache, and lymphocytic CSF, guiding the choice of profile matching. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing support for viral meningitis diagnosis. Choice B is incorrect due to indicating bacterial infection, which often results from overinterpreting pleocytosis. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 10
A 24-year-old woman presents with 2 days of fever, severe headache, and progressive confusion. She has nausea and vomited twice. Past history includes recurrent oral HSV-1 lesions. Medications: oral contraceptive only. On exam, T 39.4°C, BP 118/72 mm Hg, HR 112/min. She is disoriented to place and has word-finding difficulty. Cranial nerves are intact. She has mild right arm weakness (4/5) and hyperreflexia on the right. Neck is mildly stiff. CBC shows WBC 14,800/µL. Basic metabolic panel is normal. Concern for CNS infection is high, but focal neurologic deficits raise concern for increased intracranial pressure or a focal lesion. The team must decide on the safest next diagnostic step before CSF sampling to avoid herniation risk and to support empiric management decisions.
- Immediate lumbar puncture with opening pressure
- Noncontrast head CT before lumbar puncture (correct answer)
- MRI spine with contrast
- Carotid CT angiography
- No imaging; start antibiotics only and reassess
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, headache, confusion, and focal weakness, guiding the choice of head CT. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid assessment for mass effect or increased ICP before lumbar puncture. Choice A is incorrect due to risking herniation without ruling out contraindications, which often results from underestimating focal deficits. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 11
A 54-year-old man presents with thunderclap headache and brief loss of consciousness. Exam shows nuchal rigidity. Noncontrast head CT is negative. Lumbar puncture shows elevated RBCs in all tubes and xanthochromia. He is started on nimodipine. The team now needs to identify the bleeding source to plan definitive therapy. Which neuroimaging modality is most appropriate to evaluate for an intracranial aneurysm?
- CT angiography of the cerebral vessels (correct answer)
- Noncontrast CT of the head
- MRI cervical spine
- Carotid duplex ultrasonography
- Electromyography
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes thunderclap headache and positive LP for SAH, guiding the choice of vascular imaging. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing evaluation for aneurysm as the bleeding source. Choice B is incorrect due to low sensitivity for aneurysm, which often results from repeating initial tests. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 12
A 36-year-old man presents with progressive ascending weakness for 4 days after a diarrheal illness. He has difficulty climbing stairs and tingling in his feet. No fever now. Exam shows symmetric lower-extremity weakness (3/5), areflexia at the knees and ankles, and intact sensation to pinprick. Cranial nerves are intact. Respiratory rate is 18/min. MRI spine is unremarkable. Lumbar puncture is performed to support the suspected diagnosis and help guide monitoring. Which CSF finding is most consistent with Guillain-Barré syndrome?
- High protein with normal WBC count (correct answer)
- Low glucose with neutrophilic pleocytosis
- Oligoclonal bands with elevated IgG index
- Xanthochromia with elevated RBCs
- Marked eosinophilia with very low glucose
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes ascending weakness and areflexia, guiding the choice of lumbar puncture. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing evidence of albuminocytologic dissociation in Guillain-Barré syndrome. Choice B is incorrect due to suggesting infection, which often results from confusing inflammatory responses. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 13
A 63-year-old woman presents with sudden left-sided weakness and neglect that began 2 hours ago. She has atrial fibrillation on apixaban. Glucose is 98 mg/dL. Noncontrast head CT shows no hemorrhage. Because she is on a direct oral anticoagulant, IV thrombolysis is not planned. The stroke team considers whether she may benefit from mechanical thrombectomy and needs imaging to identify a large-vessel occlusion rapidly. Which neuroimaging modality is most appropriate next?
- CT angiography of the head and neck (correct answer)
- MRI brain with gadolinium
- Carotid duplex ultrasonography only
- Skull radiographs
- Lumbar puncture for CSF analysis
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute weakness on anticoagulation, guiding the choice of vascular imaging. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid detection of large-vessel occlusion for thrombectomy. Choice B is incorrect due to being less efficient for vessels, which often results from preferring detailed over urgent imaging. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 14
A 45-year-old woman presents with 3 weeks of worsening headaches and morning vomiting. She reports blurred vision and has had 2 episodes of brief confusion. Exam shows papilledema and mild left-sided weakness. Vitals are normal and she is afebrile. Because increased intracranial pressure from a mass lesion is a concern, clinicians must choose initial neuroimaging before considering lumbar puncture. Which neuroimaging modality is most appropriate for the initial evaluation?
- MRI brain with and without contrast (correct answer)
- Lumbar puncture for opening pressure first
- Electroencephalography
- CT of the abdomen and pelvis
- Carotid duplex ultrasonography
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes worsening headaches, papilledema, and weakness, guiding the choice of brain MRI. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing detailed evaluation for mass lesions causing increased ICP. Choice B is incorrect due to herniation risk without imaging, which often results from rushing to LP. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 15
A 70-year-old woman presents with acute right-sided weakness and slurred speech that began 30 minutes ago. She has a history of intracerebral hemorrhage 2 years ago. BP is 210/110 mm Hg. She is somnolent. The team needs rapid imaging to evaluate for recurrent hemorrhage and guide blood pressure management and neurosurgical planning. Which neuroimaging modality is most appropriate for the initial evaluation?
- Noncontrast CT of the head (correct answer)
- MRI brain with gadolinium
- CT of the lumbar spine
- MR venography
- Lumbar puncture for CSF analysis
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute weakness, hypertension, and prior ICH history, guiding the choice of noncontrast head CT. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing rapid detection of recurrent hemorrhage. Choice B is incorrect due to being less urgent for bleed, which often results from delaying with advanced imaging. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 16
A 57-year-old man presents with acute onset vertigo, nausea, and gait instability that began 1 hour ago. Exam shows left-sided limb ataxia and dysmetria; strength is full. No headache. Concern exists for posterior circulation stroke. Noncontrast head CT is obtained and shows no hemorrhage. The team wants the most sensitive imaging to detect early ischemia in the posterior fossa and guide management. Which neuroimaging modality is most appropriate next?
- MRI brain with diffusion-weighted imaging (correct answer)
- Repeat noncontrast CT in 24 hours
- Lumbar puncture for CSF protein
- Skull radiographs
- CT of the sinuses
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes acute vertigo and ataxia, guiding the choice of MRI with DWI. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing sensitive detection of posterior circulation ischemia. Choice B is incorrect due to low sensitivity early on, which often results from relying on CT alone. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 17
A 23-year-old man presents with fever, headache, and neck stiffness for 2 days. He is alert, with no focal deficits and no papilledema. He received antibiotics at an urgent care clinic earlier today. Lumbar puncture shows WBC 1,500/µL (80% neutrophils), protein 180 mg/dL, glucose 30 mg/dL (serum 95 mg/dL). Gram stain shows no organisms. The team must interpret the CSF findings to determine the most likely diagnosis despite a negative Gram stain.
- Partially treated bacterial meningitis (correct answer)
- Viral meningitis
- Multiple sclerosis
- Subarachnoid hemorrhage
- Idiopathic intracranial hypertension
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, neck stiffness, and neutrophilic CSF post-antibiotics, guiding the choice of diagnosis. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing recognition of partially treated bacterial meningitis. Choice B is incorrect due to mismatched pleocytosis, which often results from ignoring antibiotic history. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 18
A 34-year-old man presents with fever, headache, and confusion. He has no focal deficits. CT head is normal. Lumbar puncture shows WBC 90/µL (lymphocytes), protein 75 mg/dL, glucose 65 mg/dL (serum 105 mg/dL). CSF PCR returns positive for HSV-1. The team must choose the most appropriate next step after obtaining these CSF results to prevent neurologic morbidity.
- Start IV acyclovir (correct answer)
- Start oral amoxicillin
- Start IV amphotericin B
- Stop antivirals and observe only
- Start high-dose IV methylprednisolone only
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes fever, confusion, and positive HSV PCR, guiding the choice of antiviral therapy. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing targeted treatment for HSV encephalitis. Choice D is incorrect due to ignoring PCR results, which often results from underappreciating molecular diagnostics. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 19
A 72-year-old man develops progressive headache and mild confusion over 2 weeks after a fall in which he struck his head. He takes aspirin daily. No fever. Exam shows mild left arm weakness and slowed speech. Vitals are stable. Noncontrast head CT shows a crescent-shaped extra-axial collection over the right cerebral hemisphere with midline shift. The team must determine the most likely diagnosis based on the imaging description to guide neurosurgical consultation.
- Epidural hematoma
- Subdural hematoma (correct answer)
- Subarachnoid hemorrhage
- Intraparenchymal hemorrhage
- Lacunar infarct
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes progressive headache and weakness post-fall, guiding the choice of CT interpretation. The correct answer, B, is appropriate because it aligns with the clinical presentation and current guidelines, providing identification of subdural hematoma's crescent shape. Choice A is incorrect due to typical lens shape in epidural, which often results from confusing hematoma types. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.
Question 20
A 28-year-old woman presents with acute unilateral vision loss and eye pain worsened by movement. She also reports intermittent numbness in her right hand over the past year. Exam shows decreased visual acuity and a relative afferent pupillary defect. MRI brain demonstrates multiple periventricular plaques, and MRI cervical spine shows a short-segment T2 hyperintense lesion. A lumbar puncture is obtained to strengthen diagnostic certainty. Which additional test would confirm the suspected condition based on the CSF profile?
- CSF oligoclonal bands by isoelectric focusing (correct answer)
- CSF Gram stain and bacterial culture
- CSF VDRL test
- CSF cryptococcal antigen
- CSF cytology for malignant cells
Explanation: This question tests USMLE Step 2 CK skills in neuroimaging and cerebrospinal fluid analysis, focusing on appropriate test selection and interpretation. Neuroimaging and CSF analysis are critical in diagnosing and managing neurologic conditions, requiring knowledge of when and how to apply these tests. In this vignette, the patient's presentation includes vision loss and MRI plaques, guiding the choice of additional CSF testing. The correct answer, A, is appropriate because it aligns with the clinical presentation and current guidelines, providing support for multiple sclerosis via oligoclonal bands. Choice B is incorrect due to targeting infection, which often results from misinterpreting demyelination. Teaching strategies include reinforcing the decision tree approach to imaging and CSF analysis, emphasizing guideline-based practice, and reviewing case studies that illustrate common pitfalls.