A 51-year-old man comes to the office due to nausea and fatigue for the past several weeks. The patient has had occasional episodes of bilateral flank pain over the past several years and nocturia 2 or 3 times per night for the past 10 years. He has had no change in appetite or weight. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 36.9 C (98.4 F), blood pressure is 164/100 mm Hg, pulse is 80/min, and respirations are 16/min. BMI is 24 kg/m². Cardiopulmonary examination shows no abnormalities. The liver is enlarged, and a mass is felt at the right flank on deep palpation. The prostate is mildly enlarged and nontender. There is no extremity edema. Laboratory results are as follows: Which of the following best explains this patient's findings?

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Explanation: 11ec25c8_d4f1_19ba_bc81_c3e0178b8923_MD0003_00 This patient likely has chronic kidney disease (CKD) (elevated creatinine, nausea, fatigue) due to autosomal dominant polycystic kidney disease (ADPKD). In patients with ADPKD, the onset and worsening of clinical manifestations generally correlate with the progression of cystic structural degeneration of the kidneys: Flank pain, with or without hematuria, can frequently occur and may represent cyst rupture or nephrolithiasis. A flank mass can be palpable (as in this patient). Hypertension is an early disease manifestation that results from cyst enlargement leading to localized renal ischemia and increased secretion of renin with activation of the renin-angiotensin-aldosterone system. Polyuria and nocturia (as seen in this patient) with accompanying polydipsia result from a urinary concentrating defect, likely caused by cystic damage to nephron distal tubules with impaired receipt of vasopressin signals. In effect, a mild, nephrogenic diabetes insipidus is created. Progressive renal dysfunction eventually occurs due to cystic progression. Based on laboratory results, this patient likely has advanced CKD with associated anemia. Patients with ADPKD are generally asymptomatic until their 30s (or later) and develop end-stage renal disease by age 55-60. Features of ADPKD that occur outside the kidneys include liver cysts (evidenced in this patient by an enlarged liver) and cerebral aneurysms. (Choice A) Bladder outlet obstruction can occur due to benign prostate hyperplasia (BPH) and can lead to obstructive nephropathy and CKD. However, BPH would not explain an enlarged liver and right flank mass and is less likely in this patient with only a mildly enlarged prostate. (Choice B) Horseshoe kidney is a congenital abnormality associated with increased rates of ureteropelvic junction obstruction, nephrolithiasis, vesicoureteric reflux, and chronic urinary tract infection. It would not explain this patient's bilateral flank pain and enlarged liver. (Choice C) Patients with ADPKD are at increased risk of nephrolithiasis. Although nephrolithiasis can cause recurrent flank pain, it would not explain liver enlargement and would likely be diagnosed before causing advanced CKD. (Choice E) Renal cell carcinoma (RCC) can present with a unilateral flank mass but would not explain this patient's advanced CKD and is less likely in the absence of hematuria, fever, and weight loss. The incidence of RCC may be slightly increased in ADPKD, if at all. Educational objective: The clinical manifestations of autosomal dominant polycystic kidney disease generally correlate with the progression of cystic structural degeneration of the kidneys and include hypertension, polyuria, flank pain, and renal dysfunction. Extrarenal manifestations include liver cysts and cerebral aneurysms. References: Polycystic kidney disease: inheritance, pathophysiology, prognosis, and treatment. (http://www.ncbi.nlm.nih.gov/pubmed/21694932)

A 51-Year-Old Man Comes to the Office Due to Nausea