USMLE Step 1 Practice Questions and answers (Complete Solution Graded A+)

A 38-year-old man presents to the emergency department due to seizures that started earlier that day, as reported by his sister. He adds that his vision is also blurry. The patient says he has never traveled outside of the United States. Physical examination reveals several enlarged cervical lymph nodes as well as a right homonymous hemianopia. Laboratory studies show a CD4 count of 78 cells/μL. The patient is sent for an MRI with ring-enhancing lesion. - Toxoplasma Gondii Occurs in patients with HIV whose CD4 count is <100 cells/μL. It most commonly manifests with encephalitis characterized by seizures and/or focal neurologic deficits. The classic picture on a CT scan or an MRI of the head is a ring-enhancing lesion with surrounding edema and mass effect (as shown in this MRI). The specific visual field defect in this patient is due to the cerebral lesions causing a focal neurologic deficit. New-onset seizures in an HIV-positive patient with a CD4 count <100 cells/µL is highly suggestive of toxoplasmosis. Other manifestations are chorioretinitis, which is characterized by eye pain and decreased visual acuity, as seen in this patient. A 34-year-old man presents to the emergency department with a dry cough, low-grade fevers, and difficulty breathing that becomes progressively worse with exertion. He says that he has had these symptoms for the past 2-3 weeks. He reports feeling increasingly fatigued and has had an unintentional weight loss of 10 pounds (4.5 kilograms) in the same time period. The patient denies any alcohol, tobacco, or illicit drug use but admits to having had multiple sexual partners without using protection. The patient's temperature is 38.1oC (100.6oF), blood pressure is 102/72 mm Hg, pulse is 96/min, respiratory rate is 22/min, and SpO2 is 86% on room air. Physical examination shows oral thrush, bilateral rales at the lung bases, and right axillary and left inguinal lymphadenopathy. - Inhibition of Folate Synthesis