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USMLE Step 1 Practice Questions and answers 2024/25 RATED A+
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USMLE Step 1 Practice Questions and answers 2024/25 RATED A+
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USMLE Step 1 Practice Questions andanswers 2024/25 RATED A+
A 38-year-old man presents to the emergency department due to seizures that started
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earlier that day, as reported by his sister. He adds that his vision is also blurry. The patient
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says he has never traveled outside of the United States. Physical examination reveals
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several enlarged cervical lymph nodes as well as a right homonymous hemianopia.
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Laboratory studies show a CD4 count of 78 cells/μL. The patient is sent for an MRI with
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ring-enhancing lesion. - Toxoplasma Gondii
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Occurs in patients with HIV whose CD4 count is <100 cells/μL. It most commonly manifests
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with encephalitis characterized by seizures and/or focal neurologic deficits. The classic
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picture on a CT scan or an MRI of the head is a ring-enhancing lesion with surrounding
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edema and mass effect (as shown in this MRI). The specific visual field defect in this
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patient is due to the cerebral lesions causing a focal neurologic deficit.
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New-onset seizures in an HIV-positive patient with a CD4 count <100 cells/µL is highly ii ii ii ii ii ii ii ii ii ii ii ii ii
suggestive of toxoplasmosis. Other manifestations are chorioretinitis, which is
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characterized by eye pain and decreased visual acuity, as seen in this patient.
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A 34-year-old man presents to the emergency department with a dry cough, low-grade
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fevers, and difficulty breathing that becomes progressively worse with exertion. He says
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that he has had these symptoms for the past 2-3 weeks. He reports feeling increasingly
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fatigued and has had an unintentional weight loss of 10 pounds (4.5 kilograms) in the same
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time period. The patient denies any alcohol, tobacco, or illicit drug use but admits to having
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had multiple sexual partners without using protection. The patient's temperature is 38.1oC
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(100.6oF), blood pressure is 102/72 mm Hg, pulse is 96/min, respiratory rate is 22/min,
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and SpO2 is 86% on room air. Physical examination shows oral thrush, bilateral rales at
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the lung bases, and right axillary and left inguinal lymphadenopathy. - Inhibition of Folate
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Synthesis
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This patient presents with fever, dyspnea on exertion, and unintentional weight loss, which
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are suggestive of pneumonia. He also has a history of unprotected sex with multiple
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partners, and presents with oral thrush and inguinal lymphadenopathy, which are
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suggestive of HIV. Taken together, the patient's presentation and history raise suspicion of
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an opportunistic infection, such as Pneumocystis jirovecii (PCP) pneumonia. PCP
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pneumonia is an AIDS-defining illness and is typically seen in patients with CD4 counts
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<200 cells/mm. P. jirovecii is an ascomycetous fungi that also causes pneumonia in
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hematopoietic-cell and solid-organ transplant recipients, cancer patients, and patients
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receiving glucocorticoids, chemotherapeutic agents, and other immunosuppressive
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medications. The standard treatment for this illness is trimethoprim-sulfamethoxazole
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(TMP-SMX), a combination antibiotic that synergistically inhibits folate synthesis by
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inhibiting dihydrofolate reductase and dihydropteroate synthetase. If the patient has a
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sulfa-drug allergy, the treatment of choice would be pentamidine.
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A previously healthy 5-year-old boy is brought to the pediatrician with a 3-day history of
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sore throat, conjunctivitis, rhinitis, and cough. His mother explains that more than 10
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