Foundational Science and Mechanisms of Disease

A 54-year-old man with a body mass index of 34 kg/m² comes to the clinic for a follow-up visit regarding his newly diagnosed type 2 diabetes mellitus. He reports struggling to adhere to his prescribed diet and exercise regimen. Laboratory studies show a fasting plasma glucose of 145 mg/dL and a hemoglobin A1c of 7.6%. The physician initiates metformin therapy and explains that the patient's condition is primarily driven by peripheral insulin resistance, which is characterized by a blunted intracellular response to endogenous insulin in target tissues. Place the following molecular events in the correct chronological sequence representing the normal cellular mechanism of insulin-mediated glucose uptake in skeletal muscle, from initial hormone binding to the final physiological effect.

A 28-year-old female patient is evaluated at an outpatient clinic to establish primary care. She has no specific complaints, exercises regularly, and reports feeling well. She does not take any medications, over-the-counter supplements, or illicit substances. Her family history is notable for a father who was told he had "high blood calcium" years ago but never required surgery. Vital signs are within normal limits. Physical examination reveals a non-palpable thyroid gland and normal deep tendon reflexes.

Laboratory evaluation shows:
Serum calcium: $11.3$ mg/dL (Normal: $8.4-10.2$ mg/dL)
Serum albumin: $4.1$ g/dL (Normal: $3.5-5.0$ g/dL)
Serum phosphorus: $3.0$ mg/dL (Normal: $2.5-4.5$ mg/dL)
Intact parathyroid hormone: $58$ pg/mL (Normal: $15-65$ pg/mL)
24-hour urinary calcium: $42$ mg/24 hr (Normal: $100-300$ mg/24 hr)

Which of the following best describes the underlying molecular mechanism responsible for this patient's laboratory findings?

A 35-year-old man is hospitalized for the treatment of infective endocarditis and is currently receiving his first dose of intravenous penicillin G. Ten minutes into the infusion, he develops severe pruritus, a sensation of throat tightness, and sudden shortness of breath. His temperature is 37.1°C (98.8°F), blood pressure is 82/50 mm Hg, pulse is 122/min, and respirations are 26/min. Physical examination reveals diffuse urticaria across his torso and audible expiratory wheezing.

Arrange the following management and diagnostic steps in the most appropriate chronological order for this patient's acute condition.

A 45-year-old woman presents to the dermatology clinic for evaluation of a suspicious skin lesion on her left posterior thigh. She states that a 'mole' she has had for over a decade has recently grown larger, developed irregular borders, and acquired varied shades of brown, black, and blue. Excisional biopsy confirms malignant melanoma with a Breslow depth of 1.8 mm. The foundational pathogenesis of this disease typically follows a well-described, stepwise evolution of cellular and structural changes. Arrange the following histopathologic and cellular phases of this patient's neoplastic process in the correct chronological sequence of classical development, from the earliest initial lesion to the most advanced stage.

A physician evaluates multiple patients presenting with clinical signs of thyrotoxicosis (e.g., tachycardia, weight loss, tremor). Match the following thyroid diagnostic profiles (comprising Free T4, TSH, Radioactive Iodine Uptake [RAIU], and Thyroglobulin) with their corresponding primary pathophysiologic mechanism.

A 62-year-old man presents to the clinic with a 1-month history of progressive proximal muscle weakness, primarily affecting his thighs and hips. He reports significant difficulty climbing stairs and rising from a seated position, but notes that his strength temporarily improves after a few minutes of continuous walking. He has a 45-pack-year smoking history. Physical examination reveals decreased deep tendon reflexes in the lower extremities and proximal muscle weakness that transiently improves following repetitive muscle contraction. A basic metabolic panel, including serum calcium, is within normal limits. A chest radiograph demonstrates a $4.5$-cm, centrally located left lung mass with associated hilar adenopathy. Which of the following best describes the underlying pathogenesis of this patient's neurologic symptoms and the most appropriate next step in his care?

A physician evaluates an ambulatory patient who recently developed a progressively worsening rash on both lower extremities. The patient also reports significant new-onset fatigue and bilateral pain in the metacarpophalangeal and knee joints over the past $14$ days. Medical history is significant for a diagnosis of chronic hepatitis C virus (HCV) infection confirmed several years ago, though the patient has not undergone any targeted antiviral treatment. On physical examination, the physician notes multiple non-blanching, raised, red-purple lesions distributed over the shins and calves. Joint examination shows mild, symmetric swelling without warmth. Laboratory analysis demonstrates the following:

Serum aspartate aminotransferase: $85$ U/L
Serum alanine aminotransferase: $92$ U/L
Rheumatoid factor: Positive
Complement C3: Normal
Complement C4: Markedly decreased
Urinalysis: $2+$ protein, $15$-$20$ red blood cells/hpf, occasional dysmorphic red blood cells

Which of the following immunopathologic mechanisms is most likely responsible for this patient's current clinical presentation?

Match each pediatric patient's clinical presentation with the underlying primary immunologic defect.

Match each clinical and pathologic description of a hematologic malignancy with its defining molecular or cytogenetic mechanism.

Emergency medical services bring a 23-year-old male to the emergency department after his roommate found him diaphoretic, lethargic, and disoriented. The patient has a history of type 1 diabetes mellitus and recently increased his running mileage. Capillary blood glucose on arrival is 34 mg/dL. The physician promptly administers an intramuscular injection of a counter-regulatory peptide hormone, resulting in a rapid improvement of the patient's mental status and a steady rise in blood glucose over the next 15 minutes. Arrange the following intracellular and enzymatic steps in the correct chronological sequence detailing the hepatic mechanism by which this treatment reversed the patient's hypoglycemia.

A 45-year-old man is evaluated in the hospital due to a new-onset diffuse rash and severe diarrhea. He underwent an allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia four weeks ago. His current medications include tacrolimus, acyclovir, and fluconazole. His temperature is 38.2°C (100.8°F), blood pressure is 110/70 mm Hg, and pulse is 98/min. Physical examination reveals a generalized maculopapular rash that prominently involves the palms and soles. His abdomen is mildly tender to palpation, and he reports having 6 to 8 large-volume watery stools daily over the past three days. Laboratory studies show markedly elevated alkaline phosphatase and total bilirubin levels. Which of the following best describes the primary immunopathologic mechanism responsible for this patient's current clinical presentation?

A 62-year-old woman is evaluated in the intensive care unit for sudden-onset high fever, rigors, and altered mental status. Five days ago, she received chimeric antigen receptor (CAR) T-cell therapy for relapsed diffuse large B-cell lymphoma. Her temperature is 39.8°C (103.6°F), blood pressure is 82/45 mm Hg, pulse is 134/min, and respirations are 28/min. Oxygen saturation is 88% on room air. Physical examination reveals a lethargic patient with warm, flushed extremities. Cytokine release syndrome (CRS) is suspected, though concurrent sepsis cannot be excluded. Arrange the following management steps in the most appropriate chronological sequence for this patient's acute immunologic complication.

A 58-year-old man with a 10-year history of type 2 diabetes mellitus is brought to the emergency department by his wife due to severe nausea, vomiting, and generalized weakness for the past 48 hours. He recently had a viral upper respiratory infection and has had poor oral intake. His medications include metformin, empagliflozin, and lisinopril. Vital signs show a blood pressure of $98/62$ mmHg, heart rate of $115$/min, and respiratory rate of $24$/min. Physical examination reveals dry mucous membranes.

Laboratory studies show:

Arterial blood gas analysis reveals a pH of $7.24$.

Which of the following is the most direct underlying metabolic mechanism precipitating this patient's primary acid-base disturbance?

A 61-year-old man is diagnosed with advanced non-small cell lung cancer. Immunohistochemical analysis of his biopsy specimen reveals a high tumor mutational burden and robust expression of programmed death-ligand 1 (PD-L1). He is initiated on pembrolizumab, an immune checkpoint inhibitor. The pathogenesis of this patient's pre-treatment immune evasion relies on a specific sequence of cellular interactions collectively known as adaptive immune resistance. Arrange the following pathophysiological events in the chronological order that leads to tumor-induced T-cell anergy.

Match each patient's clinical presentation with the autoantibody most specifically associated with their underlying immunologic pathology.

A $58$-year-old man is evaluated in the emergency department for severe, acute-onset pain, swelling, and redness of his right knee. He is a renal transplant recipient and his current immunosuppressive regimen includes azathioprine, tacrolimus, and low-dose prednisone. He also has a history of peptic ulcer disease with a recent gastrointestinal hemorrhage. His temperature is $37.8^\circ\text{C}$ ($100.0^\circ\text{F}$). Serum laboratory studies show a creatinine level of $2.9\text{ mg/dL}$ and a uric acid level of $5.8\text{ mg/dL}$ (normal: $4.0-8.5\text{ mg/dL}$). Joint aspiration yields cloudy synovial fluid with a leukocyte count of $55,000/\mu\text{L}$ ($85\%$ neutrophils) and negatively birefringent, needle-shaped crystals. Due to the patient's medical history, several standard therapies are deemed high-risk. The physician decides to administer a targeted biologic agent appropriate for the acute management of this condition. Inhibition or neutralization of which of the following is the primary mechanism of action of the most appropriate therapy for this patient's current symptoms?

Match each clinical presentation of a paraneoplastic syndrome with its specific underlying pathophysiologic mechanism.

A 28-year-old woman presents for follow-up after a recent hospital admission for an unprovoked deep vein thrombosis in her right lower extremity. She has no significant past medical history, does not smoke, and does not take oral contraceptives. Her mother had a pulmonary embolism at age 42. Laboratory evaluation demonstrates that the addition of activated protein C (APC) to the patient's plasma fails to appropriately prolong the activated partial thromboplastin time (aPTT). Which of the following is the most likely molecular mechanism underlying this patient's condition?

A 32-year-old man is diagnosed with human immunodeficiency virus (HIV) infection. His CD4 T-lymphocyte count is 450 cells/mm $^3$ and his HIV RNA viral load is 45,000 copies/mL. The physician plans to initiate an antiretroviral therapy regimen that includes abacavir. Before prescribing this medication, the physician orders a genetic test to prevent a potentially fatal, immune-mediated hypersensitivity reaction. The specific host allele being tested for encodes a protein that is normally involved in which of the following cellular processes?

A 35-year-old woman presents to the clinic to discuss her risk for breast cancer. Her mother and maternal aunt were both diagnosed with breast cancer in their early 40s. The patient's mother recently underwent genetic testing and was told she has a pathogenic BRCA1 mutation. The patient is currently asymptomatic but is requesting genetic testing for herself to understand her risk. Arrange the following steps in the most appropriate standard sequence for the clinical genetic evaluation and management of this patient.