Foundational Science and Mechanisms of Disease

A 45-year-old man comes to the clinic for a routine follow-up examination of type 2 diabetes mellitus. His current regimen includes metformin and a newly added oral antihyperglycemic medication, which was started four weeks ago. The patient reports that his home fasting blood glucose readings have improved significantly. However, he has noticed that his shoes feel tighter and he has gained 2.5 kg (5.5 lb) since his last visit. He has a history of mild heart failure with preserved ejection fraction. Physical examination reveals 2+ bilateral pitting edema of the lower extremities. Laboratory studies show a fasting plasma glucose of 112 mg/dL. The physician realizes the new medication is responsible for the patient's fluid retention, which is exacerbating his underlying cardiac condition, and plans to discontinue it immediately. The discontinued drug most likely exerts its primary therapeutic effect by initially binding to which of the following cellular targets?

Match each patient's clinical presentation of a suspected paraneoplastic syndrome with the most likely underlying neoplastic etiology and its associated pathophysiologic mechanism.

A 46-year-old man comes to the clinic for a follow-up visit regarding poorly controlled hypertension. Over the past 4 months, his blood pressure has consistently been in the 160s/100s mmHg despite adherence to maximum doses of amlodipine and lisinopril. He reports new-onset generalized muscle weakness, fatigue, and frequent urination. His medical history is significant for chronic dyspepsia, for which he recently began consuming large quantities of a European herbal black candy. He does not use tobacco or illicit drugs. Blood pressure is $168/98$ mmHg, and pulse is 78/min. Physical examination reveals no edema, normal secondary sexual characteristics, and no striae or easy bruising.

Laboratory studies show:
Serum sodium: 146 mEq/L
Serum potassium: 2.5 mEq/L
Serum chloride: 101 mEq/L
Serum bicarbonate: 32 mEq/L
Plasma renin activity: 0.1 ng/mL/hr (normal: 0.6-4.3 ng/mL/hr)
Plasma aldosterone: 1.2 ng/dL (normal: 3.0-30.0 ng/dL)
Morning serum cortisol: 16 $\mu$ g/dL (normal: 5-23 $\mu$ g/dL)

Which of the following best describes the specific molecular mechanism responsible for this patient's clinical and laboratory presentation?

A 22-year-old man presents to the gastroenterology clinic for evaluation of intermittent bright red blood per rectum over the past two months. He reports no abdominal pain, unexplained weight loss, or changes in stool caliber. His father died of metastatic colorectal cancer at age 38, and a paternal aunt underwent abdominal surgery for an unknown malignancy in her 30s. His temperature is 37.0°C (98.6°F), blood pressure is 118/76 mmHg, pulse is 72/min, and respirations are 14/min. Physical examination reveals a soft, non-tender abdomen without organomegaly. Digital rectal examination demonstrates normal sphincter tone with small amounts of bright red blood on the examining finger. Given his striking family history, a colonoscopy is performed and reveals over 150 small adenomatous polyps carpeting the entire colon and rectum. Biopsies of several polyps confirm tubular adenomas with low-grade dysplasia. Which of the following best describes the underlying foundational mechanism of this patient's condition and the most appropriate definitive management?

A hospital laboratory is reviewing several distinct metabolic profiles of patients with disorders of calcium homeostasis. Match each patient's serum and urine biochemical profile to the most likely underlying pathophysiological mechanism.

A 28-year-old woman is admitted to the medical ward with a 3-day history of high fever, marked facial swelling, and a widespread skin eruption. She reports that the rash began on her face and upper trunk before spreading to her extremities. Four weeks ago, she was prescribed sulfasalazine for newly diagnosed inflammatory bowel disease. Her temperature is 39.2°C (102.6°F), blood pressure is 110/70 mmHg, and pulse is 112/min. Physical examination reveals prominent periorbital edema, generalized cervical lymphadenopathy, and a diffuse, confluent, erythematous maculopapular rash covering 70% of her body surface area. There is no mucosal ulceration or epidermal detachment. Laboratory studies show:

Leukocyte count: $18,500/\text{mm}^3$
Eosinophils: $2,500/\text{mm}^3$ (normal: $15–500/\text{mm}^3$)
Alanine aminotransferase (ALT): 450 U/L
Aspartate aminotransferase (AST): 410 U/L
Serum creatinine: 1.1 mg/dL

Which of the following best describes the predominant immunopathologic mechanism driving this patient's clinical syndrome?

A $32$-year-old man comes to the clinic to establish care. He feels well and has no medical problems. He takes no medications. Vital signs are within normal limits. Routine laboratory testing reveals a serum calcium level of $11.2$ mg/dL (N: $8.4$-$10.2$ mg/dL) and a serum intact parathyroid hormone level of $55$ pg/mL (N: $15$-$65$ pg/mL). A $24$-hour urine collection shows a calcium excretion of $45$ mg/day (N: $100$-$300$ mg/day). The urine calcium-to-creatinine clearance ratio is calculated to be $0.005$ (normal $>0.02$). His mother also has a history of mild, asymptomatic hypercalcemia that was treated with a parathyroidectomy in her $30$ s without resolution of the hypercalcemia. Which of the following best describes the cellular mechanism underlying this patient's laboratory findings?

Match each patient's clinical presentation with the precise immunopathologic mechanism responsible for their condition.

A 44-year-old man presents to the oncology clinic for treatment planning of newly diagnosed metastatic colorectal cancer. He initially presented to his primary care physician with fatigue and was found to have iron deficiency anemia. A subsequent colonoscopy revealed a 3.5-cm ulcerated mass in the ascending colon, and a computed tomography scan of the abdomen and pelvis showed multiple hepatic metastases. His family history is notable for his father dying of colon cancer at age 48 and a paternal aunt who was treated for endometrial cancer at age 46.

Physical examination reveals pale conjunctivae and a palpable liver edge 3 cm below the right costal margin. Laboratory studies show a hemoglobin of 9.2 g/dL.

Biopsy of the hepatic lesion confirms metastatic adenocarcinoma. Immunohistochemical staining of the biopsy specimen demonstrates intact expression of MLH1 and PMS2 proteins, but absent expression of MSH2 and MSH6 proteins. The oncologist recommends initiating therapy with a programmed cell death protein 1 (PD-1) inhibitor.

Which of the following molecular characteristics best explains why this patient's neoplasm is highly susceptible to this specific pharmacologic therapy?

A 32-year-old woman with severe symptomatic iron deficiency anemia is admitted to the hospital and started on a transfusion of packed red blood cells. Fifteen minutes after the transfusion is initiated, she acutely develops chills, severe lower back pain, and a feeling of impending doom. Her temperature is 39.1°C (102.4°F), blood pressure is 88/54 mm Hg, heart rate is 124/min, and respiratory rate is 24/min. Physical examination reveals flushing and diaphoresis. An acute hemolytic transfusion reaction is suspected. Arrange the following steps in the most appropriate chronological sequence for the immediate management and diagnostic workup of this patient.

Match each patient's clinical presentation with the primary molecular mechanism of immune evasion or pathogenesis utilized by the causative organism.

Correlate each infectious disease scenario with the specific cellular mechanism of its causative bacterial toxin.

Match each clinical scenario describing a patient with an advanced malignancy who has developed acquired resistance to a targeted antineoplastic therapy with the most likely underlying molecular mechanism of resistance.

Match each patient's clinical presentation and advanced hemostatic laboratory findings with the correct underlying pathophysiological mechanism of their coagulation disorder.

A 28-year-old primigravida at 14 weeks gestation is brought to the emergency department by her husband due to progressive confusion, lethargy, and recurrent vomiting over the past 24 hours. The husband reports that her symptoms began shortly after they attended a celebratory dinner where she consumed a large portion of steak. The patient has a lifelong history of self-restricting meat and dairy from her diet, stating they make her feel "foggy and irritable." Family history is notable for a male sibling who died at 4 days of life from a "metabolic coma."

Physical examination reveals a somnolent woman who arouses to physical stimuli. She exhibits a flapping tremor of the hands when her wrists are extended.

Laboratory studies are as follows:

Urinalysis reveals markedly elevated orotic acid levels.

Which of the following genetic principles best explains why this patient survived to adulthood while her sibling experienced early neonatal mortality?

A medical geneticist is reviewing the charts of several adult and pediatric patients with complex genetic presentations. To finalize their diagnostic formulations and targeted management plans, match each patient's clinical presentation and preliminary genetic findings to the precise underlying molecular or targeted therapeutic mechanism.

Match each bacterial pathogen's primary virulence toxin with its precise molecular mechanism of action.

A 28-year-old aid worker presents to a field clinic with severe, voluminous watery diarrhea and leg cramps. The responsible pathogen produces an AB-type exotoxin that causes profound fluid loss. Arrange the following steps of this toxin's cellular mechanism of action in the correct pathophysiological sequence, from initial interaction with the host cell to the ultimate physiologic effect.

A 45-year-old man undergoes a right hemicolectomy for a colon adenocarcinoma. His family history is notable for a father who died of colorectal cancer at age 49 and a sister diagnosed with endometrial cancer at age 46. The physician suspects Lynch syndrome and plans a comprehensive molecular and genetic evaluation.

Assuming this patient's cancer is ultimately found to be caused by a germline mutation in the MLH1 gene, arrange the following diagnostic and management steps in the most appropriate chronological order.

A 24-year-old woman is brought to the emergency department 36 hours after intentionally ingesting a massive quantity of an unknown over-the-counter analgesic. She is visibly jaundiced and lethargic. Laboratory studies show an aspartate aminotransferase (AST) of 8,500 U/L, an alanine aminotransferase (ALT) of 9,200 U/L, and a significantly prolonged prothrombin time. A subsequent liver biopsy reveals massive centrilobular (Zone 3) parenchymal necrosis. Based on the patient's presentation, arrange the following subcellular biochemical events in the correct chronological sequence that culminated in this patient's hepatocyte injury.