A 81-year-old man presents to his cardiologist for ongoing management of mild heart failure. He has not had any changes in his cardiac function status and says that he is tolerating lisinopril without any major side effects. During the course of the visit, the patient says that he is unhappy with his urologist because he has been experiencing episodes of dizziness after starting prazosin for benign prostatic hyperplasia. He says that he feels these episodes were caused by malpractice on his urologist's behalf and is considering a lawsuit against his urologist. Which of the following is the most appropriate course of action for the cardiologist?

Encourage the patient to speak with his urologist directly

Call the urologist and warn him of an impending lawsuit

Call the urologist to convey the patient's dissatisfaction

Contact his insurance agent to discuss possible risks

Sympathize with the patient's desire for a lawsuit

A drug research team has synthesized a novel oral drug that acts as an agonist at multiple adrenergic receptors. When administered in animals, it has been shown to produce urinary retention at therapeutic doses with the absence of other manifestations of adrenergic stimulation. The researchers are interested in understanding signal transduction and molecular mechanisms behind the action of the novel drug. Which of the following receptors would most likely transduce signals across the plasma membrane following the administration of this novel drug?

GqPCRs (Gq protein-coupled receptors)

GoPCRs (Go protein-coupled receptors)

GsPCRs (Gs protein-coupled receptors)

GtPCRs (Gt protein-coupled receptors)

GiPCRs (Gi protein-coupled receptors)

A 30-year-old obese female presents with new-onset headaches, ringing in her ears, and blurry vision. Ibuprofen and avoidance of light has not relieved her symptoms. She denies a history of recent trauma, fever, chills, and fatigue. Past medical history is significant for type 2 diabetes mellitus managed with metformin. She has had 20/20 vision her whole life and wonders if she might need to get eyeglasses. She has 2 healthy school-age children. Her temperature is 36.8°C (98.2°F), heart rate is 90/min, respiratory rate is 15/min, and blood pressure is 135/80 mm Hg. Physical exam is notable for decreased lateral eye movement, and the funduscopic findings are shown in the picture. Laboratory findings are within normal limits and brain imaging is normal. Lumbar puncture demonstrates an elevated opening pressure and normal CSF composition. Which of the following is a side effect of the medication used to treat this condition?

Decreased white blood cell count

A 37-year-old woman presents to the Emergency Department after 8 hours of left sided flank pain that radiates to her groin and pelvic pain while urinating. Her medical history is relevant for multiple episodes of urinary tract infections, some requiring hospitalization, and intravenous antibiotics. In the hospital, her blood pressure is 125/83 mm Hg, pulse of 88/min, a respiratory rate of 28/min, and a body temperature of 36.5°C (97.7°F). On physical examination, she has left costovertebral tenderness and lower abdominal pain. Laboratory studies include a negative pregnancy test, mild azotemia, and a urinary dipstick that is positive for blood. Which of the following initial tests would be most useful in the diagnosis of this case?

Fractional excretion of sodium (FeNa+)

Contrast abdominal computed tomography

Blood urea nitrogen (BUN): serum creatinine (SCr) ratio

A 23-year-old woman comes to the emergency department for the evaluation of mild retrosternal pain for the last 7 hours after several episodes of self-induced vomiting. The patient was diagnosed with bulimia nervosa 9 months ago. Her only medication is citalopram. She is 170 cm (5 ft 7 in) tall and weighs 62 kg (136.6 lb); BMI is 21.5 kg/m2. She appears pale. Her temperature is 37°C (98.6°F), pulse is 75/min, respirations are 21/min, and blood pressure is 110/75 mm Hg. The lungs are clear to auscultation. Cardiac examinations shows no murmurs, rubs, or gallops. The abdomen is soft and nontender with no organomegaly. The remainder of the physical examination shows swelling of the salivary glands, dry skin, and brittle nails. An ECG and an x-ray of the chest show no abnormalities. Contrast esophagram with gastrografin shows mild leakage of contrast from the lower esophagus into the mediastinum without contrast extravasation into the pleural and peritoneal cavities. Which of the following is the most appropriate next step in the management?

Intravenous ampicillin and sulbactam therapy

A 27-year-old woman comes to the emergency department because of progressive numbness and weakness in her left arm and left leg for 2 days. During this period, she has also had urinary urgency and incontinence. Three months ago, she had blurry vision, difficulty distinguishing colors, and headache for one week, all of which have resolved. The patient has smoked a half pack of cigarettes daily for 10 years and drinks four glasses of wine each week. Her temperature is 37°C (98.6°F), pulse is 78/min, respirations are 14/min, and blood pressure is 110/68 mm Hg. Examination shows 3/5 strength in the left arm and leg, and 5/5 strength on the right side. Upon flexion of the neck, the patient experiences a shooting electric sensation that travels down the spine. MRI of the brain shows gadolinium-enhancing lesions in the right central sulcus, cervical spinal cord, and optic nerve. Which of the following is the most appropriate next step in the management of this patient?

Administer IV methylprednisolone

Administer tissue plasminogen activator

A 74-year-old male is brought to the emergency department 1 hour after he fell from the top of the staircase at home. He reports pain in his neck as well as weakness of his upper extremities. He is alert and immobilized in a cervical collar. He has hypertension treated with hydrochlorothiazide. His pulse is 90/min and regular, respirations are 18/min, and blood pressure is 140/70 mmHg. Examination shows bruising and midline cervical tenderness. Neurologic examination shows diminished strength and sensation to pain and temperature in the upper extremities, particularly in the hands. Upper extremity deep tendon reflexes are absent. Strength, sensation, and reflexes in the lower extremities are intact. Anal sensation and tone are present. Babinski's sign is absent bilaterally. Which of the following is most likely to confirm the cause of this patient's neurologic examination findings?

MRI of the cervical spine without contrast

CT of the cervical spine with contrast

Contrast studies for USMLE Step 3: High-Yield Anatomy Lessons

Contrast Fundamentals - Making Tissues Talk

Principle: Agents that alter tissue X-ray attenuation or magnetic properties to increase conspicuity of structures or fluids.
Positive Contrast (Radiopaque):
- Appear white/bright (↑ attenuation).
- Examples: Iodinated compounds (IV, arterial), Barium Sulfate (GI tract).
Negative Contrast (Radiolucent):
- Appear black/dark (↓ attenuation).
- Examples: Air, CO₂.

⭐ Gadolinium, the primary MRI contrast agent, is linked to Nephrogenic Systemic Fibrosis (NSF) in patients with severe renal dysfunction (GFR < 30 mL/min).

Iodinated Contrast - CT's Shining Star

Mechanism: Iodine (high atomic number) attenuates X-rays → structures appear hyperdense (bright white). Crucial for visualizing vasculature, organs, and pathologies.
Formulations:
- Low-Osmolar (LOCM): The modern standard. Far lower risk of adverse reactions compared to older high-osmolar agents.
- Iso-Osmolar (IOCM): Osmolality same as blood; may be safer in high-risk patients (e.g., severe renal impairment).
Kinetics & Safety:
- Excreted by kidneys; always check baseline creatinine/eGFR.
- ⚠️ Contrast-Induced Nephropathy (CIN): AKI within 48-72 hrs. Prevent with IV hydration.
- ⚠️ Metformin: Hold if eGFR <30 or patient has AKI, to prevent lactic acidosis.

⭐ A prior "allergy" to shellfish is NOT a contraindication to iodinated contrast; the allergy is to proteins, not iodine.

Gadolinium Contrast - MRI's Magnetic Helper

Mechanism: Paramagnetic agent. Shortens the T1 relaxation time of nearby water protons, leading to a brighter signal (T1 hyperintensity) in tissues where it accumulates.
Primary Uses:
- Detecting and characterizing tumors, inflammation, and infections.
- Assessing blood-brain barrier integrity.
- Magnetic Resonance Angiography (MRA) for vessel imaging.

MRI Brain: Ring-enhancing lesion with gadolinium contrast

Major Adverse Effect:
- ⚠️ Nephrogenic Systemic Fibrosis (NSF): A rare, severe fibrosing disease affecting skin and internal organs.
- Strongly associated with patients having severe renal dysfunction (GFR < 30 mL/min/1.73m²).

⭐ High-Yield: Always screen for renal impairment before administering gadolinium. The risk of NSF is highest with older, linear chelating agents compared to newer macrocyclic agents.

Clinical Safety - The Contrast Checklist

Allergies: Prior reaction to contrast? Shellfish allergy is NOT a contraindication.
Bleeding: On anticoagulants? Check PT/INR/PTT.
Contrast Nephropathy Risk: Check eGFR. Hold NSAIDs.
Drugs: Metformin, beta-blockers, interleukins.

📌 Mnemonic: ABCD for pre-contrast safety.

⭐ Metformin & Contrast: Hold metformin on the day of and for 48 hours after IV contrast if eGFR is < 60 mL/min/1.73m² or in patients with known hepatic dysfunction or alcoholism. Resume only after re-checking renal function.

Iodinated contrast carries a risk of contrast-induced nephropathy (CIN), especially with pre-existing renal disease or diabetes.

Gadolinium is linked to nephrogenic systemic fibrosis (NSF) in patients with severe renal impairment (low GFR).

Barium sulfate is contraindicated in suspected bowel perforation; use water-soluble agents like gastrografin instead.

Withhold metformin for 48 hours after iodinated contrast to prevent lactic acidosis if CIN occurs.

Pre-medicate for prior anaphylactoid reactions with corticosteroids.

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