A 40-year-old man comes to the emergency department due to acute flank pain and dysuria. He has no associated fever, joint pain, or suprapubic pain. The patient was discharged 5 days ago following hospitalization for central nervous system toxoplasmosis. He has long-standing AIDS (most recent CD4 count: 150/mm³) and had not been compliant with either antiretroviral treatment or trimethoprim-sulfamethoxazole prophylaxis therapy for several months prior to admission. While in the hospital, the patient was started on sulfadiazine and pyrimethamine, and antiretroviral treatment was reinstituted.
Temperature is 37 C (98.6 F) , blood pressure is 122/78 mm Hg, and pulse is 98/min. Mucous membranes are dry. The abdomen is soft, and bilateral costovertebral angle tenderness is present. No rash is present.
Laboratory studies are as follows:
A urinary catheter is placed and produces 10 mL of urine during 6 hours of observation in the emergency department.
Which of the following is most likely to confirm the diagnosis in this patient?

Question

A 40-year-old man comes to the emergency department due to acute flank pain and dysuria. He has no associated fever, joint pain, or suprapubic pain. The patient was discharged 5 days ago following hospitalization for central nervous system toxoplasmosis. He has long-standing AIDS (most recent CD4 count: 150/mm³) and had not been compliant with either antiretroviral treatment or trimethoprim-sulfamethoxazole prophylaxis therapy for several months prior to admission. While in the hospital, the patient was started on sulfadiazine and pyrimethamine, and antiretroviral treatment was reinstituted.
Temperature is 37 C (98.6 F) , blood pressure is 122/78 mm Hg, and pulse is 98/min. Mucous membranes are dry. The abdomen is soft, and bilateral costovertebral angle tenderness is present. No rash is present.
Laboratory studies are as follows:

A urinary catheter is placed and produces 10 mL of urine during 6 hours of observation in the emergency department.
Which of the following is most likely to confirm the diagnosis in this patient?

Quizplus · Accepted Answer

11ec193a_98fb_0dac_853d_8d0f0848fb9d_MD0002_00 This patient has acute kidney injury (AKI) with hematuria, pyuria, and bilateral costovertebral angle tenderness. The recent initiation of sulfadiazine should raise suspicion for crystal-induced AKI, which occurs when poorly soluble drugs precipitate within the renal tubules. Factors favoring crystal formation include exposure to high doses of the drug, dehydration (increases intratubular concentration), and acidic urinary pH (occurs with uric acid, sulfonamides, and methotrexate). Patients are often asymptomatic, but can have flank pain; symptoms typically occur within a week of drug initiation. Diagnosis is confirmed by observation of characteristic crystals on urinalysis when the patient is taking a known inciting drug. Hematuria and pyuria are also commonly noted. Nearly 30% of patients on sulfadiazine develop AKI, primarily due to the drug's insolubility at a urinary pH of ≤5.5. Sulfonamides can form needle-shaped, rosette, or clumped ("stacks of wheat") crystals that can be identified on urinalysis. Prevention and treatment of sulfadiazine-induced AKI include adequate hydration (3 L/day) and alkalinization of the urine to a pH of >7.15 to increase solubility. In patients with suspected sulfadiazine-induced AKI, renal ultrasound can be obtained to complete the evaluation but is unlikely to confirm the diagnosis. Ultrasonography can be normal, show sludge or small calyceal stones (due to sulfonamide precipitation), or reveal hydronephrosis (in rare cases where urolithiasis develops and causes obstructive uropathy). However, these findings are nonspecific and are unlikely to change initial management with fluids and urine alkalinization to solubilize the crystals. If urolithiasis is suspected in a nonpregnant patient, noncontrast CT scan is preferred to ultrasound as it is more sensitive and accurate (Choice B). (Choice A) Cystoscopy can detect bladder cancer or stones, which usually present with painless hematuria or irritative voiding symptoms. This patient's flank pain and costovertebral tenderness are more consistent with an upper urinary tract etiology. (Choice C) Pyelonephritis causes flank pain and costovertebral angle tenderness, although it is typically unilateral. However, patients who develop AKI from pyelonephritis are typically quite ill; fever, chills, and hypotension would be expected. (Choice E) Acute interstitial nephritis commonly presents with fever, rash, and eosinophilia. Urinalysis classically shows urine eosinophils and white blood cell casts (not seen in this patient). In addition, pain is uncommon. Educational objective: Crystal-induced acute kidney injury occurs when poorly soluble drugs precipitate in the renal tubules. Sulfadiazine is insoluble at a pH of ≤5.5; prevention and treatment include hydration and alkalinization of the urine to a pH of >7.15 to increase solubility. __________

A 40-Year-Old Man Comes to the Emergency Department Due to Acute