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Difficulty: HardGeneral Internal Medicine

Match each patient's clinical presentation with the most accurate underlying pathophysiologic description.

  • A 68-year-old man with a history of severe chronic obstructive pulmonary disease is evaluated in the acute care clinic for worsening somnolence and a productive cough. Arterial blood gas on room air shows a pH of 7.247.24, pCO 2_2 of 7272 mm Hg, and calculated HCO 3−_3^- of 3030 mEq/L.Alveolar hypoventilation causing acute-on-chronic respiratory acidosis
  • A 55-year-old man with progressive fatigue and deep, rapid breathing (Kussmaul respirations) has laboratory testing showing Na +^+ 140140 mEq/L, Cl −^- 104104 mEq/L, and HCO 3−_3^- 1212 mEq/L, alongside markedly elevated blood urea nitrogen and creatinine levels.Retention of unmeasured organic acids causing a high anion gap metabolic acidosis
  • A 72-year-old woman who recently completed a 10-day course of oral levofloxacin for a respiratory tract infection now presents with profuse, foul-smelling, watery diarrhea. Her laboratory results show a leukocyte count of 22,000/mm322,000 / \text{mm}^3.Microbial dysbiosis leading to proliferation of a spore-forming obligate anaerobe
  • A 32-year-old woman recently started on oral methimazole for hyperthyroidism reports to the clinic with a sudden onset of rigors and severe odynophagia. A complete blood count reveals an absolute neutrophil count of 200/mm3200 / \text{mm}^3.Idiosyncratic immune-mediated arrest of myelopoiesis

Answer

The clinical vignettes correctly match to: COPD exacerbation with acute-on-chronic respiratory acidosis, uremic high anion gap metabolic acidosis, antibiotic-associated Clostridioides difficile colitis, and methimazole-induced agranulocytosis.
Each matching pair requires identifying the primary diagnosis from the vignette and mapping it to its formal pathophysiologic description. The first patient has alveolar hypoventilation (COPD exacerbation). The second has uremic acidosis (high anion gap). The third has C. difficile colitis (microbial dysbiosis). The fourth has methimazole-induced agranulocytosis (immune-mediated myelopoiesis arrest).

Step-by-Step Solution

1
Evaluate the arterial blood gas for the first patient to determine the primary disturbance.
Identified primary respiratory acidosis with partial metabolic compensation.
Allows accurate classification of the acid-base derangement caused by the acute COPD exacerbation.
2
Calculate the anion gap using the formula: Na +^+ - (Cl −^- + HCO 3−_3^-) for the second patient.
The calculated anion gap is 2424 mEq/L, confirming a high anion gap metabolic acidosis.
Differentiates between normal and high anion gap metabolic acidosis in a patient with renal failure.
3
Assess the temporal relationship between levofloxacin use and the onset of profound leukocytosis and diarrhea in the third patient.
Identifies a high clinical suspicion for Clostridioides difficile colitis.
Broad-spectrum antibiotics disrupt normal flora, leading to opportunistic toxigenic infections.
4
Correlate the initiation of methimazole with the profound neutropenia (ANC 200/mm3200 / \text{mm}^3) in the fourth patient.
Identifies drug-induced agranulocytosis.
Prompt recognition of this idiosyncratic drug toxicity is critical to stop the offending agent and prevent fatal sepsis.

Key Concept

Integration of diverse clinical presentations in general internal medicine, requiring multi-step diagnosis of acid-base disturbances, nosocomial infections, and severe adverse drug reactions based on physical findings and laboratory data.
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General Internal Medicine

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