Question

A 35-year-old man with known autosomal dominant polycystic kidney disease (ADPKD) presents with sudden-onset right flank pain and mild hematuria. He denies fever, dysuria, or recent trauma. Ultrasound shows enlarged cystic kidneys with no evidence of renal mass. Which of the following is least likely to be the cause of flank pain in this condition?

• A. Cyst hemorrhage
• B. Urinary tract infection
• C. Nephrolithiasis
• D. Renal cell carcinoma

Hint:

In ADPKD patients presenting with acute pain + fever, suspect an infected cyst. The diagnostic challenge is that infected cysts often do not show up well on standard CT or ultrasound. An FDG-PET scan or MRI is sometimes required to definitively localize an infected cyst.

Answer 1

The Correct Option is D

Concept:
Autosomal Dominant Polycystic Kidney Disease (ADPKD) is characterized by the progressive development of innumerable cysts in both kidneys.
Acute flank pain in an ADPKD patient is a very common presentation and necessitates differentiating among several frequent complications.
The question asks to identify the least likely etiology for his sudden flank pain.
Explanation:
• The most common causes of acute flank or abdominal pain in a patient with ADPKD include cyst hemorrhage, cyst infection (or generalized UTI/pyelonephritis), and nephrolithiasis.

• Cyst hemorrhage (Option A) occurs due to the rupture of stretched, fragile blood vessels in the cyst wall. It presents exactly as described: sudden-onset, severe localized pain, often accompanied by gross or microscopic hematuria.

• Nephrolithiasis (Option C) is highly prevalent in ADPKD (up to 20-30% of patients), largely due to urinary stasis from distorted anatomy and metabolic factors like hypocitraturia. It typically presents with acute colicky flank pain and hematuria.

• Urinary tract infection/cyst infection (Option B) is another major complication. While this patient denies fever, atypical or early infections can still cause localized flank pain.

• Renal Cell Carcinoma (RCC) (Option D) is a malignant tumor. While ADPKD patients can develop RCC, the incidence is not definitively higher than in the general population. More importantly, an RCC typically presents as a slowly growing solid mass, causing insidious, dull pain over a long period, rather than "sudden-onset" acute pain. Furthermore, the ultrasound showed no evidence of a solid renal mass, effectively ruling it out as the immediate cause of the sudden pain.

• Therefore, RCC is the least likely cause of this acute presentation.
Final answer:
Renal cell carcinoma is the least likely cause of sudden-onset flank pain in this scenario, as ADPKD primarily features hemorrhage, stones, or infection.