Foundational Science and Mechanisms of Disease

A 38-year-old man is evaluated in the hospital for a progressive rash and severe diarrhea. Five weeks ago, he underwent a matched-unrelated donor allogeneic hematopoietic stem cell transplantation for acute lymphoblastic leukemia. His conditioning regimen included total body irradiation and high-dose cyclophosphamide. Over the past four days, he has developed a diffuse, pruritic maculopapular rash that prominently involves his palms, soles, and posterior trunk. He also reports crampy abdominal pain and large-volume, watery diarrhea, with nursing staff measuring approximately 1.5 liters of stool output yesterday. Vital signs are temperature 38.1°C (100.6°F), blood pressure 110/70 mmHg, heart rate 98/min, and respiratory rate 16/min. Physical examination confirms the described rash and reveals mild scleral icterus. Laboratory studies show:

Total bilirubin: 4.8 mg/dL
Direct bilirubin: 3.5 mg/dL
Alkaline phosphatase: 420 U/L
Aspartate aminotransferase (AST): 85 U/L
Alanine aminotransferase (ALT): 92 U/L

Which of the following best describes the primary immunopathogenesis of this patient's current clinical syndrome?

Correlate the following specific cellular and molecular biopsy findings with the targeted pharmacologic agent most appropriate for exploiting that underlying neoplastic mechanism.

An obstetrician is asked to evaluate a patient in the emergency department. The patient, pregnant with twins at $10$ weeks gestation, has been experiencing intractable vomiting, leading to severe dehydration and a weight loss of $4\text{ kg}$ ($8.8\text{ lbs}$) over the last two weeks. During the evaluation, the physician notes a resting heart rate of $115/\text{min}$ and a fine resting tremor. The patient mentions she feels constantly hot despite the room being air-conditioned. Examination of the neck reveals no thyromegaly or cervical lymphadenopathy, and eye examination is unremarkable.

Initial laboratory investigations show a human chorionic gonadotropin (hCG) level of $245,000\text{ mIU/mL}$, a suppressed thyroid-stimulating hormone (TSH) level of $0.05\text{ \mu U/mL}$, and an elevated free thyroxine (free T4) level of $2.5\text{ ng/dL}$.

Which of the following best explains the cellular mechanism underlying this patient's abnormal thyroid laboratory profile?

A 29-year-old man is evaluated in the hypertension clinic for persistently elevated blood pressure. He was diagnosed with hypertension at age 21 and is currently taking maximally tolerated doses of amlodipine, lisinopril, and chlorthalidone with poor control. He reports occasional muscle cramps but no headaches, palpitations, or diaphoresis. Family history is notable for his father, who developed severe hypertension in his twenties and died of a hemorrhagic stroke at age 42.

Blood pressure is 168/104 mm Hg and heart rate is 76/min. BMI is 24 kg/m². Physical examination reveals no abdominal bruits, striae, or abnormal fat distribution.

Laboratory results are as follows:

An unenhanced CT scan of the abdomen demonstrates bilateral adrenal enlargement without discrete masses. Following a 4-week therapeutic trial with low-dose oral dexamethasone, the patient's blood pressure decreases to 126/82 mm Hg and serum potassium rises to 4.3 mEq/L.

Which of the following is the most likely molecular mechanism underlying this patient's condition?

A 64-year-old man presents to the emergency department with a 4-day history of severe, crampy abdominal pain and 8 to 10 watery, non-bloody bowel movements daily. He was diagnosed with metastatic non-small cell lung cancer 3 months ago. Genomic testing of his tumor revealed high expression of a ligand that binds to an inhibitory T-cell receptor. Based on these findings, he recently began targeted monoclonal antibody therapy, receiving his last infusion 10 days ago. His temperature is 37.9°C (100.2°F), blood pressure is 102/65 mm Hg, and pulse is 112/min. Physical examination reveals dry mucous membranes and diffuse abdominal tenderness without rigidity, rebound, or guarding. Laboratory studies show a serum creatinine of 1.4 mg/dL (baseline 0.9 mg/dL) and a white blood cell count of 11,500/mm³. Rapid stool testing for Clostridioides difficile toxin is negative. Which of the following is the most appropriate next step in management?

A 38-year-old patient is admitted to the diagnostic evaluation unit for recurrent episodes of diaphoresis, palpitations, and confusion that resolve rapidly with carbohydrate intake. A supervised 72-hour fasting test is initiated, and comprehensive laboratory studies are drawn when the patient develops symptomatic hypoglycemia (capillary blood glucose 42 mg/dL). Match each distinct laboratory profile below with its most likely underlying pathophysiologic mechanism.

A 42-year-old man presents to the hospital with a 2-day history of low-grade fever, malaise, decreased urine output, and allograft tenderness. He underwent a deceased-donor kidney transplantation 2 months ago. His current medications include tacrolimus, mycophenolate mofetil, and prednisone. His serum creatinine has abruptly increased from a baseline of $1.3 \text{ mg/dL}$ to $2.9 \text{ mg/dL}$. Initial laboratory studies show a subtherapeutic serum tacrolimus trough level. Urinalysis reveals mild proteinuria but is negative for infection.

Arrange the following steps in the most appropriate sequence for the continued evaluation and management of this patient's allograft dysfunction, from initial structural evaluation to the escalation of therapy for refractory immunologic disease.

A $66$-year-old man presents to the internal medicine clinic for a routine health maintenance visit. He reports a six-month history of mild urinary urgency, frequency, and nocturia, but denies any weight loss, bone pain, hematuria, or dysuria. He has no significant past medical history. Examination reveals a slightly enlarged, firm, and asymmetric prostate. As part of a comprehensive evaluation for a potential neoplastic process of the prostate, the physician considers the appropriate diagnostic and therapeutic algorithm.

Arrange the following diagnostic and management steps in the most appropriate chronological order according to current oncologic guidelines.

A 62-year-old man comes to the clinic for a routine follow-up. He has a 10-year history of type 2 diabetes mellitus and a history of heart failure with preserved ejection fraction (ejection fraction of $55\%$). His current medications include metformin, lisinopril, and amlodipine. He feels well and reports no shortness of breath, orthopnea, or lower extremity edema. His blood pressure is $128/78 \text{ mm Hg}$, and his pulse is $72/\text{min}$. Physical examination reveals clear lungs bilaterally and no jugular venous distention. Laboratory evaluation shows a hemoglobin A1c of $8.6\%$. The physician considers adding pioglitazone to the patient's regimen to improve glycemic control but decides against it due to the patient's cardiac history. Which of the following best describes the cellular mechanism by which the avoided medication promotes fluid retention?

An internist is evaluating a 48-year-old man who reports a 3-month history of persistent nasal crusting, recurrent epistaxis, and migratory arthralgias. Over the past two weeks, the patient has developed a cough that occasionally produces blood-tinged sputum. He has no prior medical history and takes no medications. Vital signs are within normal limits except for a blood pressure of 152/94 mm Hg. Physical examination reveals an ulcerated septal mucosa and a saddle-nose deformity. Laboratory testing shows a blood urea nitrogen of 38 mg/dL and a serum creatinine of 2.6 mg/dL. Urinalysis demonstrates 2+ protein, numerous dysmorphic red blood cells, and red blood cell casts. Which of the following immunopathologic mechanisms is most directly responsible for this patient's renal findings?

A physician is managing a 45-year-old female patient who presents with resistant hypertension and spontaneous hypokalemia. Diagnostic testing reveals an elevated plasma aldosterone concentration to plasma renin activity ratio, and abdominal imaging confirms a unilateral adrenal adenoma. The patient's condition results in excessive sodium reabsorption in the distal nephron. Arrange the following cellular events in the correct chronological sequence to describe the physiological mechanism of action for the hormone overproduced in this condition.

For each of the following clinical scenarios requiring targeted biologic therapy, select the precise immunopathologic mechanism of the most appropriate therapeutic agent.

A 47-year-old woman comes to the clinic reporting worsening fatigue, increased thirst, and frequent urination over the past three months. She has a history of chronic cough and was told she had "enlarged lymph nodes" in her chest a year ago, but she did not follow up. Her temperature is 37.0°C (98.6°F), blood pressure is 128/82 mmHg, and pulse is 78/min. Physical examination reveals a few erythematous nodules on her anterior lower legs. Laboratory studies show:

Which of the following cellular mechanisms best explains this patient's current laboratory abnormalities?

A 58-year-old man comes to the clinic reporting a two-month history of a persistent left-sided scrotal mass that feels like a 'bag of worms.' The mass does not decrease in size when he lies flat. He also reports intermittent episodes of pink-tinged urine over the past month. His past medical history is significant for a 30-pack-year smoking history, though he quit 5 years ago. His vital signs show a blood pressure of 150/95 mmHg, heart rate 82/min, and a BMI of 28 kg/m2. Physical examination confirms a left-sided varicocele that remains prominent in the supine position. Laboratory testing reveals a hemoglobin of 19.2 g/dL and a hematocrit of 58%. Which of the following best describes the molecular or pathophysiologic mechanism most directly responsible for the laboratory abnormality seen in this patient?

Various hereditary cancer syndromes are characterized by distinct clinical presentations and specific underlying molecular defects. Match each patient's clinical vignette with the fundamental genetic mechanism responsible for their disease pathogenesis.

A 24-year-old woman is brought to the emergency department by her husband due to a 12-hour history of severe, progressively worsening abdominal pain, nausea, and multiple episodes of nonbilious vomiting. She has not had any fever, diarrhea, or melena. Her medical history is significant for several episodes of sudden-onset, nonpruritic lip and facial swelling over the past five years that typically resolved spontaneously after 2 to 3 days. Her father had a history of similar recurrent episodes of facial swelling. On physical examination, her temperature is 37.1°C (98.8°F), blood pressure is 110/70 mm Hg, pulse is 105/min, and respiratory rate is 16/min. The abdomen is diffusely tender with guarding but no rebound tenderness. There is no cutaneous rash, urticaria, or wheezing. A CT scan of the abdomen with intravenous contrast demonstrates segmental small bowel wall thickening and free pelvic fluid, without evidence of bowel obstruction. Laboratory evaluation shows a normal complete blood count, a normal basic metabolic panel, and a significantly decreased serum C4 level.

Administration of an agent with which of the following mechanisms of action is most appropriate for the acute management of this patient's current symptoms?

A 58-year-old man presents to the emergency department with profound weakness and an inability to stand. He has a 40-pack-year smoking history. Over the past three months, he has experienced a $12\text{ kg}$ ($26\text{ lb}$) weight loss and noticed darkening of his skin creases. Two weeks ago, his primary care physician started him on lisinopril and hydrochlorothiazide for new-onset hypertension. His blood pressure is $165/95\text{ mm Hg}$. Physical examination reveals temporal wasting, proximal muscle weakness, and hyperpigmentation of the palmar creases.

Laboratory studies show:
Sodium: $144\text{ mEq/L}$
Potassium: $2.1\text{ mEq/L}$
Chloride: $98\text{ mEq/L}$
Bicarbonate: $35\text{ mEq/L}$
Morning serum cortisol: $92\text{ }\mu\text{g/dL}$ (Reference: $5-23\text{ }\mu\text{g/dL}$)
Plasma ACTH: $480\text{ pg/mL}$ (Reference: $10-60\text{ pg/mL}$)

Based on the clinical presentation and laboratory findings, which of the following is the primary cellular mechanism responsible for this patient's profound hypokalemia?

A $19$-year-old male of West African descent is admitted to the inpatient oncology unit for the initiation of induction chemotherapy after being diagnosed with bulky Burkitt lymphoma. His baseline renal function and electrolyte panels are within normal limits. Thirty-six hours after starting a cytotoxic regimen containing cyclophosphamide, doxorubicin, vincristine, and methotrexate, he reports severe nausea, muscle twitching, and significantly reduced urine output.

An electrocardiogram shows peaked T waves. Laboratory evaluation reveals the following:

The attending physician plans to prescribe a recombinant urate oxidase enzyme to rapidly lower the patient's uric acid levels. Which of the following patient factors represents an absolute contraindication to this specific pharmacologic intervention?

Emergency medical services transport a 22-year-old woman to the hospital after her roommate found her lethargic and confused. Over the past 12 hours, she has experienced a high fever, repeated vomiting, and profuse diarrhea. Her medical history is notable for severe epistaxis, for which an anterior nasal packing was placed at an urgent care clinic three days ago. Current vital signs are temperature 39.5°C (103.1°F), blood pressure 82/45 mmHg, pulse 135/min, and respiratory rate 24/min. Physical examination reveals a diffuse, erythematous, macular rash that resembles a severe sunburn covering her trunk and extremities. Her sclerae are markedly injected, and the oral mucosa is hyperemic. The nasal packing remains in place and appears saturated. Which of the following best describes the molecular mechanism responsible for this patient's rapid hemodynamic collapse?

An ambulance brings a 68-year-old male patient to the acute care unit due to altered mental status and hyperventilation that began earlier today. His wife reports that he had a severe gastrointestinal illness over the last three days with profound watery diarrhea, leading to significantly decreased oral fluid intake. His past medical history is significant for hypertension, stable angina, and type 2 diabetes mellitus. He has continued to take his prescribed daily medications despite his recent illness.

Physical examination reveals a lethargic, difficult-to-arouse patient with deep, rapid respirations. Vital signs include a blood pressure of 88/54 mm Hg, heart rate of 115/min, and respiratory rate of 28/min. The abdomen is diffusely tender but soft.

Initial laboratory evaluation shows:
- Sodium: 138 mEq/L
- Potassium: 5.2 mEq/L
- Chloride: 98 mEq/L
- Bicarbonate: 10 mEq/L
- Blood urea nitrogen: 54 mg/dL
- Creatinine: 3.2 mg/dL (baseline was 1.4 mg/dL one month ago)
- Glucose: 145 mg/dL
- Lactate: 9.5 mmol/L (Normal: 0.5 - 2.2 mmol/L)

An arterial blood gas drawn on room air demonstrates a pH of 7.22 and a pCO2 of 24 mm Hg.

The drug most likely responsible for this acute presentation lowers serum glucose primarily through which of the following cellular mechanisms?