USMLE STEP 1 2024/2025 QUESTIONS AND
ANSWERS SOLVED 100%
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. ...ANSWER...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. ...ANSWER...Inhibition of Folate Synthesis
This patient presents with fever, dyspnea on exertion, and unintentional weight loss,
which are suggestive of pneumonia. He also has a history of unprotected sex with
multiple partners, and presents with oral thrush and inguinal lymphadenopathy, which
are suggestive of HIV. Taken together, the patient's presentation and history raise
suspicion of an opportunistic infection, such as Pneumocystis jirovecii (PCP)
pneumonia. PCP pneumonia is an AIDS-defining illness and is typically seen in patients
with CD4 counts <200 cells/mm. P. jirovecii is an ascomycetous fungi that also causes
, pneumonia in hematopoietic-cell and solid-organ transplant recipients, cancer patients,
and patients receiving glucocorticoids, chemotherapeutic agents, and other
immunosuppressive medications. The standard treatment for this illness is trimethoprim-
sulfamethoxazole (TMP-SMX), a combination antibiotic that synergistically inhibits folate
synthesis by inhibiting dihydrofolate reductase and dihydropteroate synthetase. If the
patient has a sulfa-drug allergy, the treatment of choice would be pentamidine.
A previously healthy 5-year-old boy is brought to the pediatrician with a 3-day history of
sore throat, conjunctivitis, rhinitis, and cough. His mother explains that more than 10
children in his class at school have similar symptoms, particularly conjunctivitis. His
temperature is 100.4°F (38°C), pulse is 108/min, and blood pressure is 110/80 mm Hg.
Physical examination shows the finding in the image. No cultures are ordered, and the
mother is assured that her son's illness will go away on its own. One week later, the
mother reports that her son is healthy and back at school. ...ANSWER...This patient
presents with many symptoms of a viral upper respiratory infection (rhinitis, sore throat,
cough) and the finding of conjunctival infection or "pink eye." He is also one of many
children in his class to have such symptoms.
He likely has an adenovirus infection, which is a major cause of epidemic
keratoconjunctivitis (pink eye). It is the fourth most common cause of childhood
respiratory tract infections after respiratory syncytial virus, parainfluenza, and rhinovirus.
It is a naked, icosahedral, double-stranded linear DNA virus that results in a self-limited
illness that requires no treatment.
Although rhinovirus (a cause of the "common cold") would cause many of the symptoms
the child is experiencing, it is less likely to cause the pink eye seen in this patient.
A 40-year-old woman presents to the physician with a 10-month history of progressive
hearing loss, dizziness, and impaired balance. Past medical history is unremarkable.
Neurologic exam reveals decreased hearing bilaterally. Dix-Hallpike maneuver does not
reproduce symptoms of vertigo, and no nystagmus is noted. MRI of the brain shows
bilateral masses at the cerebellopontine angle. Biopsy of the mass is performed and the
cells stain positive for S100 protein. ...ANSWER...The patient's constellation of
symptoms of bilateral hearing loss and vertigo is characteristic of bilateral acoustic
neuroma. Acoustic or vestibular neuromas are schwannomas localized along the CN
VIII. These tumors are classically found at the cerebellopontine angle, and the cells
stain positive for S100 protein.
The presence of bilateral acoustic neuromas is virtually pathognomonic for
neurofibromatosis (NF)-2. NF-2 is an autosomal dominant disorder characterized by the
presence of various CNS tumors, including schwannomas (tumors of Schwann cell
origin), meningiomas, and ependymomas. Schwann cells are derived from the neural
crest cells and function to myelinate peripheral nervous system neurons.
A 59-year-old man presents to the emergency department after waking up in the middle
of the night with a very severe headache. When asked about the intensity of his pain,
the patient exclaims, "I feel like my head is going to explode." Emergent CT of the head
demonstrates blood tracking down the sulci and following the contours of the pia.
ANSWERS SOLVED 100%
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. ...ANSWER...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. ...ANSWER...Inhibition of Folate Synthesis
This patient presents with fever, dyspnea on exertion, and unintentional weight loss,
which are suggestive of pneumonia. He also has a history of unprotected sex with
multiple partners, and presents with oral thrush and inguinal lymphadenopathy, which
are suggestive of HIV. Taken together, the patient's presentation and history raise
suspicion of an opportunistic infection, such as Pneumocystis jirovecii (PCP)
pneumonia. PCP pneumonia is an AIDS-defining illness and is typically seen in patients
with CD4 counts <200 cells/mm. P. jirovecii is an ascomycetous fungi that also causes
, pneumonia in hematopoietic-cell and solid-organ transplant recipients, cancer patients,
and patients receiving glucocorticoids, chemotherapeutic agents, and other
immunosuppressive medications. The standard treatment for this illness is trimethoprim-
sulfamethoxazole (TMP-SMX), a combination antibiotic that synergistically inhibits folate
synthesis by inhibiting dihydrofolate reductase and dihydropteroate synthetase. If the
patient has a sulfa-drug allergy, the treatment of choice would be pentamidine.
A previously healthy 5-year-old boy is brought to the pediatrician with a 3-day history of
sore throat, conjunctivitis, rhinitis, and cough. His mother explains that more than 10
children in his class at school have similar symptoms, particularly conjunctivitis. His
temperature is 100.4°F (38°C), pulse is 108/min, and blood pressure is 110/80 mm Hg.
Physical examination shows the finding in the image. No cultures are ordered, and the
mother is assured that her son's illness will go away on its own. One week later, the
mother reports that her son is healthy and back at school. ...ANSWER...This patient
presents with many symptoms of a viral upper respiratory infection (rhinitis, sore throat,
cough) and the finding of conjunctival infection or "pink eye." He is also one of many
children in his class to have such symptoms.
He likely has an adenovirus infection, which is a major cause of epidemic
keratoconjunctivitis (pink eye). It is the fourth most common cause of childhood
respiratory tract infections after respiratory syncytial virus, parainfluenza, and rhinovirus.
It is a naked, icosahedral, double-stranded linear DNA virus that results in a self-limited
illness that requires no treatment.
Although rhinovirus (a cause of the "common cold") would cause many of the symptoms
the child is experiencing, it is less likely to cause the pink eye seen in this patient.
A 40-year-old woman presents to the physician with a 10-month history of progressive
hearing loss, dizziness, and impaired balance. Past medical history is unremarkable.
Neurologic exam reveals decreased hearing bilaterally. Dix-Hallpike maneuver does not
reproduce symptoms of vertigo, and no nystagmus is noted. MRI of the brain shows
bilateral masses at the cerebellopontine angle. Biopsy of the mass is performed and the
cells stain positive for S100 protein. ...ANSWER...The patient's constellation of
symptoms of bilateral hearing loss and vertigo is characteristic of bilateral acoustic
neuroma. Acoustic or vestibular neuromas are schwannomas localized along the CN
VIII. These tumors are classically found at the cerebellopontine angle, and the cells
stain positive for S100 protein.
The presence of bilateral acoustic neuromas is virtually pathognomonic for
neurofibromatosis (NF)-2. NF-2 is an autosomal dominant disorder characterized by the
presence of various CNS tumors, including schwannomas (tumors of Schwann cell
origin), meningiomas, and ependymomas. Schwann cells are derived from the neural
crest cells and function to myelinate peripheral nervous system neurons.
A 59-year-old man presents to the emergency department after waking up in the middle
of the night with a very severe headache. When asked about the intensity of his pain,
the patient exclaims, "I feel like my head is going to explode." Emergent CT of the head
demonstrates blood tracking down the sulci and following the contours of the pia.
