APRENDIZAJE BASADO EN UN CASO

75-year-old man presents to the emergency department (ED) with a 6-week history of worsening lower abdominal pain. He describes the pain as sharp, constant, and associated with a weight loss of approximately 20 lb over the past month. The patient states that for the past few weeks he has also noticed bilateral lower-extremity swelling and abdominal distention. The abdominal distention has been severe enough to prevent him from bending over. He experienced an increased frequency of urination until 3 days ago; he has been anuric since then. For the past week he has not been able to tolerate solid foods, resulting in an entirely liquid diet. As of the day of presentation even liquids have become intolerable. There is also a history of numbness and tingling in both legs and an unsteady gait during the last week. He reports a feeling of confusion but is fully oriented to person, place, and time. His medical history is significant for hypertension under treatment and mitral valve insufficiency. He denies any surgical history. His current medications include daily aspirin and nifedipine. The patient has an age-appropriate level of physical activity and lives alone. He does not smoke or drink.

On physical examination, the patient is a well-oriented elderly man in no acute distress. His vital signs include an oral temperature of 97.4°F (36.3°C), a blood pressure of 211/92 mm Hg, a pulse of 104 beats/min, an unlabored respiratory rate of 20 breaths/min, and an oxygen saturation of 97% on room air. Head and neck examination reveals dry oral mucous membranes with a supple neck and no jugular venous distention. The chest examination is clear to auscultation bilaterally, with normal breath sounds and normal S1 and S2 heart sounds without murmurs, rubs, or gallops. The abdominal examination is significant for distention, mostly in the hypogastric and umbilical regions, and for the presence of a reducible umbilical hernia. Normal bowel sounds are appreciated in all quadrants. The patient's lower abdomen is diffusely tender, with slight tenderness noted in the upper abdomen as well. There is no rebound tenderness or guarding and Lloyd's sign is negative. Extremity examination is significant for bilateral pitting edema of the lower extremities. The patient has no focal neurologic abnormalities (although gait testing is deferred).

Initial laboratory investigations include a complete blood count (CBC) and basic metabolic panel. There are no significant findings on the CBC. The metabolic panel reveals a serum sodium level of 130 mEq/L (normal range, 136-145 mEq/L), potassium of 4.2 mEq/L (normal range, 3.5-5.0 mEq/L), chloride of 83 mEq/L (normal range, 95-105 mEq/L), bicarbonate of 16 mEq/L (normal range, 22-28 mEq/L), and glucose of 92 mg/dL (normal range, 70-125 mg/dL). Serum creatinine is 21.2 mg/dL (normal range, 0.6-1.2 mg/dL) and blood urea nitrogen is 120 mg/dL (normal range, 7-18 mg/dL). The calculated glomerular filtration rate (GFR) is 3 mL/min/1.73 m² (normal, ≥ 90 mL/min/1.73 m²). A CT scan of the abdomen and pelvis is obtained (Figures 1 and 2).

What is the most likely diagnosis?