Internal Medicine

Match the following laboratory profiles of calcium, phosphorus, and parathyroid hormone (PTH) to the most likely underlying pathophysiologic diagnosis.

A 24-year-old man is brought to the emergency department by his roommate due to increasing lethargy and confusion over the past 12 hours. The patient has a history of type 1 diabetes mellitus and has not taken his insulin for the past week due to financial constraints. Vital signs show a temperature of $37.1^\circ$ C ($98.8^\circ$ F), heart rate of 115/min, blood pressure of 105/68 mm Hg, and a respiratory rate of 28/min with deep, rapid breaths.

Laboratory studies reveal:

Which of the following arterial $pCO_2$ values would best indicate an appropriate, isolated respiratory compensation for this patient's acid-base disturbance?

A 64-year-old man is evaluated in the intensive care unit for abnormal laboratory findings. He was admitted 2 days ago for severe community-acquired pneumonia complicated by septic shock. He was intubated yesterday for worsening hypoxia and is currently mechanically ventilated. The patient is sedated and receiving a continuous intravenous infusion of norepinephrine. Vital signs show a temperature of $38.4^\circ\text{C}$ ($101.1^\circ\text{F}$), blood pressure of $92/58 \text{ mm Hg}$, heart rate of $118/\text{min}$, and oxygen saturation of $95\%$ on the current ventilator settings.

Laboratory studies:
Serum sodium: $140 \text{ mEq/L}$
Serum potassium: $4.1 \text{ mEq/L}$
Serum chloride: $100 \text{ mEq/L}$
Serum bicarbonate: $16 \text{ mEq/L}$
Blood urea nitrogen: $32 \text{ mg/dL}$
Serum creatinine: $1.9 \text{ mg/dL}$
Serum lactate: $5.2 \text{ mmol/L}$ (Normal: $0.5-1.5 \text{ mmol/L}$)

Arterial blood gas (on mechanical ventilation):
pH: $7.52$
$\text{PaCO}_2$: $20 \text{ mm Hg}$
$\text{PaO}_2$: $78 \text{ mm Hg}$

Which of the following is the most accurate interpretation of this patient's current acid-base status?

A 54-year-old woman comes to the clinic reporting a 2-month history of progressive weakness, particularly when climbing stairs and brushing her hair. She also notes a new rash on her face and hands. Her medical history is unremarkable, and she takes no medications. Physical examination reveals an erythematous, violaceous rash on her upper eyelids and scaling, erythematous plaques over her metacarpophalangeal and proximal interphalangeal joints. Muscle strength is 3/5 in the proximal upper and lower extremities bilaterally, and 5/5 in the distal extremities. Sensation is intact, and deep tendon reflexes are 2+ bilaterally.

The physician diagnoses the patient with dermatomyositis and plans to initiate high-dose oral prednisone. Which of the following is the most appropriate additional step in the management of this patient?

A 65-year-old man is admitted to the hospital for acute decompensated heart failure and is treated with aggressive intravenous furosemide. On hospital day 3, his blood pressure is 105/65 mm Hg and heart rate is 92/min. Over the past 24 hours, his urine output has decreased to 400 mL. His serum creatinine rises from a baseline of 1.1 mg/dL to 2.8 mg/dL.

Laboratory studies are obtained to evaluate his acute kidney injury:

Serum chemistry:
Sodium: 136 mEq/L
Potassium: 3.8 mEq/L
Chloride: 98 mEq/L
Bicarbonate: 28 mEq/L
Blood urea nitrogen (BUN): 84 mg/dL
Creatinine: 2.8 mg/dL

Urine chemistry:
Sodium: 70 mEq/L
Urea nitrogen: 420 mg/dL
Creatinine: 56 mg/dL

Because recent loop diuretic administration impairs tubular sodium reabsorption, the fractional excretion of sodium ($FE_{Na}$) can be misleadingly elevated. Instead, the fractional excretion of urea ($FE_{Urea}$) is preferred to differentiate between prerenal azotemia and intrinsic acute tubular necrosis in this clinical scenario.

Calculate the patient's $FE_{Urea}$. Express your answer as a percentage.

A 36-year-old man with a history of advanced, untreated HIV infection (CD4 count $28 \text{ cells/mm}^3$) is brought to the emergency department due to progressive confusion, severe headaches, and left-sided weakness over the past week. His temperature is $38.1^\circ\text{C}$ ($100.6^\circ\text{F}$). Neurologic examination reveals a dense left hemiparesis. MRI of the brain reveals multiple 1- to 2-cm ring-enhancing lesions in the right basal ganglia and frontal lobe with marked surrounding vasogenic edema causing a 4-mm midline shift. Serum *Toxoplasma gondii* IgG antibodies are positive.

Arrange the following clinical actions in the correct chronological sequence according to the standard management algorithm for this patient, assuming a complete lack of clinical or radiographic response to the first-line medical intervention.

Match each of the following patient presentations, which are characterized by specific acid-base and electrolyte derangements (Left), with the precise underlying cellular or transporter defect (Right).

A $32$-year-old woman comes to the clinic due to progressive fatigue, weight loss, lightheadedness, and failure to resume her menses. Ten months ago, she delivered a healthy full-term infant. The delivery was complicated by severe postpartum hemorrhage requiring an emergency blood transfusion and a brief admission to the intensive care unit. Following discharge, she was unable to produce breast milk. Her blood pressure is $88/54$ mmHg, and her pulse is $92$/min. Physical examination shows pale skin without hyperpigmentation and delayed relaxation of deep tendon reflexes. Laboratory studies show:

Which of the following is the most appropriate next step in the management of this patient?

A hospital's antimicrobial stewardship and infectious diseases teams are reviewing several complex cases involving severe adverse drug events. Match each patient's clinical presentation of an antimicrobial-induced complication to the specific pharmacologic agent most likely responsible.

A 45-year-old man with a history of poorly controlled type 2 diabetes mellitus is brought to the emergency department due to confusion, nausea, and abdominal pain for the past 2 days. He has missed his last several doses of insulin. His temperature is 37.1°C (98.8°F), blood pressure is 100/65 mm Hg, pulse is 112/min, and respirations are 24/min. Physical examination shows dry mucous membranes and a fruity breath odor.

Laboratory studies show:

What is this patient's serum anion gap (in mEq/L)?

Match each classic urinalysis sediment finding with its most likely associated renal pathology.

A $54$-year-old woman is evaluated in the ambulatory care clinic for progressive lethargy and generalized weakness over the past six months. She states she feels persistently cold even during warm weather and has been struggling with constipation. Over the same period, she has been involved in several minor motor vehicle collisions, which she attributes to "not seeing cars coming from the side." Physical examination reveals pale, dry skin, puffiness around the eyes, and a delayed relaxation phase of the deep tendon reflexes. Confrontational visual field testing demonstrates decreased peripheral vision bilaterally.

Laboratory studies reveal:
Hemoglobin: $11.2$ g/dL
Thyroid-stimulating hormone (TSH): $1.8$ $\mu$ U/mL (Normal: $0.4$-$4.0$ $\mu$ U/mL)
Free thyroxine (T4): $0.5$ ng/dL (Normal: $0.9$-$1.7$ ng/dL)

Which of the following is the most likely underlying mechanism for this patient's laboratory findings?

A 28-year-old resident physician sustains a deep percutaneous needlestick injury to her thumb while drawing arterial blood from a patient. The patient has a known history of untreated HIV with a viral load of 250,000 copies/mL. The needle is visibly contaminated with the patient's blood. Arrange the following steps in the most appropriate chronological order for the management of this occupational exposure.

A 62-year-old woman with a history of advanced non-small cell lung cancer presents to the emergency department with a three-day history of progressively worsening mid-back pain. Today, she developed bilateral leg weakness and urinary retention. Her vital signs are within normal limits. Physical examination reveals a motor strength of 3 out of 5 in the bilateral lower extremities, symmetric hyperreflexia at the patellae, and absent rectal sphincter tone. Sensory examination reveals decreased sensation to pinprick below the umbilicus. Arrange the following steps in the most appropriate chronological sequence for the management of this patient's current condition.

A $24$-year-old man schedules an appointment at an outpatient rheumatology clinic due to progressive, dull lower back pain over the past eight months. He describes the discomfort as insidious in onset, peaking during the early morning hours, and accompanied by severe stiffness that lasts approximately two hours. His symptoms are noticeably alleviated by engaging in physical exercise but worsen with prolonged rest. He denies any recent trauma, urethritis, psoriasis, or vision changes. Physical examination demonstrates limited lumbar flexion (positive Schober test) and bilateral tenderness upon palpation of the sacroiliac joints. Laboratory studies reveal an erythrocyte sedimentation rate (ESR) of $45 \text{ mm/h}$ and a C-reactive protein (CRP) level of $22 \text{ mg/L}$. Rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies are negative. The physician suspects a seronegative spondyloarthropathy and begins formulating a clinical pathway to confirm the diagnosis and establish long-term management.

Arrange the following diagnostic and therapeutic interventions in the most appropriate chronological sequence based on standard medical guidelines for this suspected condition.

A 36-year-old woman comes to the office due to severe fatigue, cold intolerance, and constipation that have progressively worsened over the past 5 months. She also reports secondary amenorrhea for the last 6 months. She takes no daily medications. Her blood pressure is 96/60 mm Hg and her pulse is 54/min. Physical examination reveals dry skin, thinning of the lateral eyebrows, and a delayed relaxation phase of the deep tendon reflexes.

Laboratory studies:
- Hemoglobin: $11.0$ g/dL
- Thyroid-stimulating hormone (TSH): $1.2 \ \mu\text{U/mL}$ (Normal: $0.5$–$5.0 \ \mu\text{U/mL}$)
- Free thyroxine (T4): $0.4$ ng/dL (Normal: $0.9$–$1.7$ ng/dL)
- Urine pregnancy test: Negative

Which of the following is the most appropriate next step in management?

Match each set of arterial blood gas (ABG) and basic metabolic panel (BMP) results with the most likely clinical scenario. Assume all values were obtained simultaneously on room air. Reference ranges: $Na^+$ 135-145 mEq/L, $Cl^-$ 98-106 mEq/L, $HCO_3^-$ 22-28 mEq/L, $pCO_2$ 35-45 mmHg, pH 7.35-7.45.

A 68-year-old woman is evaluated in the intensive care unit on hospital day 5. She was initially admitted for severe community-acquired pneumonia complicated by acute respiratory distress syndrome. She is currently intubated and receiving mechanical ventilation. Her condition is stable, and her oxygen requirements have been steadily decreasing. Her temperature is 37.2°C (99.0°F), blood pressure is 112/74 mm Hg, and pulse is 86/min. Physical examination shows crackles at the right lung base but is otherwise unremarkable. The thyroid gland is not palpable. Routine laboratory studies are obtained, and a thyroid panel shows the following results:

Which of the following is the most appropriate next step in management regarding this patient's thyroid laboratory findings?

A medical student is reviewing laboratory data for five different patients evaluated in the endocrinology clinic for suspected calcium and bone metabolism disorders. Based on the diagnostic algorithm for calcium homeostasis, match each of the following complex laboratory profiles to its most likely underlying pathophysiologic diagnosis.

Match each laboratory profile with its most likely underlying pathophysiologic diagnosis. Assume normal reference ranges for the following: Serum calcium 8.4-10.2 mg/dL, Phosphorus 2.5-4.5 mg/dL, Intact PTH 15-65 pg/mL.