An 18-year-old man comes to the emergency department with flank pain and red urine for the past day. Approximately 3 days ago, he experienced flu-like symptoms with rhinorrhea and throat pain that improved with over-the-counter acetaminophen. The patient has no chronic medical conditions and takes no daily medications. He does not use tobacco, alcohol, or illicit drugs. Family history is unremarkable. Temperature is 37.2 C (99 F), blood pressure is 126/76 mm Hg, pulse is 88/min, and respirations are 18/min. The patient has mild costovertebral tenderness. The remainder of the physical examination is normal. Laboratory results are as follows: Serum complement levels are normal. Spiral CT scan of the abdomen is normal. Which of the following is the most likely diagnosis in this patient?

Question

An 18-year-old man comes to the emergency department with flank pain and red urine for the past day.  Approximately 3 days ago, he experienced flu-like symptoms with rhinorrhea and throat pain that improved with over-the-counter acetaminophen.  The patient has no chronic medical conditions and takes no daily medications.  He does not use tobacco, alcohol, or illicit drugs.  Family history is unremarkable.  Temperature is 37.2 C (99 F), blood pressure is 126/76 mm Hg, pulse is 88/min, and respirations are 18/min.  The patient has mild costovertebral tenderness.  The remainder of the physical examination is normal.  Laboratory results are as follows:  Serum complement levels are normal.  Spiral CT scan of the abdomen is normal.  Which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c1c1_64b5_8f63_17db54449fd1_MD0005_00 This patient's gross hematuria and elevated creatinine with a recent upper respiratory tract infection (URI) raise concern for IgA nephropathy or acute poststreptococcal glomerulonephritis (APSGN). Unlike IgA nephropathy, APSGN classically presents weeks after group A Streptococcus infection (eg, pharyngitis, impetigo), and complement levels are low (Choice A). This patient's normal serum complement levels and onset of symptoms days after a URI (synpharyngitic) are suggestive of IgA nephropathy. The production of pathogenic IgA is triggered by a mucosal infection, or less commonly, it occurs spontaneously. IgA is deposited in the mesangium, leading to a spectrum of disease ranging from asymptomatic, microscopic hematuria to gross hematuria with nephritic syndrome (eg, hypertension, elevated creatinine). Flank pain (eg, costovertebral angle tenderness) is common and thought to be caused by stretching of the renal capsule. Urinalysis demonstrates proteinuria, hematuria, and red blood cell (RBC) casts. Serum complement levels are normal because of the weak complement-fixing activity of IgA. The diagnosis is typically clinical but can be confirmed with kidney biopsy. Recurrent episodes of hematuria are common, but IgA nephropathy is usually a benign disease with no chronic kidney injury. Clinical predictors of progressive disease include hypertension, elevated creatinine, and persistent proteinuria. (Choice B) Hereditary nephritis (Alport syndrome) can cause gross hematuria and progressive renal insufficiency. However, most male patients have hematuria beginning in early childhood and develop hearing loss in adolescence. This patient's unremarkable medical and family history make this diagnosis less likely. (Choice D) Nephrolithiasis causes flank pain and hematuria. However, this patient's urinary RBC casts suggest a glomerular etiology of hematuria. In addition, the spiral CT scan would be expected to demonstrate stones. (Choice E) Thin basement membrane disease is a benign familial condition that presents with episodic hematuria, which can develop after a URI; flank pain and urinary RBC casts are uncommon but can occur. However, elevated creatinine is not seen, and there is usually a family history of hematuria. Educational objective: The classic presentation of IgA nephropathy is hematuria within days of an upper respiratory infection; renal insufficiency and hypertension may be present. Laboratory evaluation shows hematuria with red blood cell casts on urinalysis and, unlike in acute poststreptococcal glomerulonephritis, normal complement levels. References: Immunoglobulin A nephropathy: a review of current literature on emerging pathophysiology. (http://www.ncbi.nlm.nih.gov/pubmed/23719511)

An 18-Year-Old Man Comes to the Emergency Department with Flank