Approach to cystic kidney disease: Clinical sciences

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Introduction 0:00–0:45

Kidney cysts are fluid-filled sacs lined by a thin wall of cells that can be located either in the cortex, the medulla, or both.
Kidney cysts can be associated with acquired or inherited renal conditions and might cause no symptoms or lead to progressive loss of renal function and end-stage renal disease.
There are several different renal conditions associated with kidney cysts, including simple renal cysts, medullary sponge kidney disease, and acquired renal cystic disease, as well as autosomal dominant polycystic kidney disease and autosomal dominant tubulointerstitial kidney disease.
If your patient presents with a chief concern suggesting cystic kidney disease, start by obtaining a focused history and physical exam.

H&P 0:45–1:36

Your patient might report symptoms specific to kidney conditions, like flank pain and hematuria. Additionally, there might be a history of kidney stones or a family history of kidney disease.
Next, the physical exam may reveal elevated blood pressure and palpable kidneys with costovertebral angle tenderness. With these findings, consider a kidney disorder.
Your next step is to order labs, including BMP, serum uric acid, and urinalysis. Also, don’t forget a renal ultrasound.
If the renal ultrasound reveals a single or multiple kidney cysts, diagnose cystic kidney disease and assess for a family history of kidney disease.
Now, if there’s no family history of kidney disease, consider simple renal cysts, medullary sponge kidney disease, or acquired renal cystic disease.

Simple Renal Cysts 1:36–2:30

When it comes to simple renal cysts, they are typically incidentally found, as they are asymptomatic with no abnormalities on the physical exam and labs.
The renal ultrasound reveals normal-sized kidneys with sharply demarcated cysts with smooth walls without septa, calcifications, or solid components.
With these findings, diagnose simple renal cysts, which typically do not require treatment or follow-ups. Here’s a clinical pearl to keep in mind!
Unlike simple cysts, complex cysts have thicker walls and may contain solid material. They are a sign of an underlying cystic kidney condition, so be sure to monitor these patients over time, as some cysts could progress to renal cell carcinoma.
Medullary Sponge Kidney Disease Next up is medullary sponge kidney disease, which is caused by a developmental malformation of the renal collecting ducts in the medulla resulting in ductal dilatation and cyst formation.

Medullary Sponge Kidney Disease2:30–3:54

This collecting duct dilatation, or ectasia, is associated with the formation of both small, meaning microscopic, and large medullary so-called "cysts" that are often diffuse but do not involve the cortex.
Due to poor reabsorption of calcium, oxalate, and uric acid, as well as stagnation of the urine, these patients often report a history of kidney stones, hematuria, and recurrent urinary tract infections.
On the flip side, their physical exam is typically normal, with normal serum creatinine levels and urinalysis revealing hematuria.
In these individuals, the ultrasound shows normal-sized kidneys with small and large cysts in the renal medulla where in the majority of cases there is associated nephrocalcinosis and kidney stones.
If you see this, consider medullary sponge kidney disease and order additional imaging methods, such as intravenous pyelogram or CT urogram.
If the imaging confirms the presence of kidney stones and nephrocalcinosis; and reveals pooling of contrast at the junction of the papilla and calyces producing a feathered- or brushlike appearance, diagnose medullary sponge kidney disease.
Moving on to acquired renal cystic disease. These patients are usually asymptomatic with a history of chronic kidney disease, particularly end-stage renal disease requiring dialysis.

Acquired renal cystic disease 3:54–4:33

The physical exam is typically normal, but their labs are significant for elevated creatinine before the renal cyst development.
Finally, the renal ultrasound shows small- to normal-sized kidneys with a smooth contour and multiple bilateral cysts. With these findings, diagnose acquired cystic disease of the kidney.
Keep in mind that these individuals are also at risk for developing renal cell carcinoma, so don’t forget to regularly monitor them.
Okay, let’s go back a step and talk about individuals with a positive family history of kidney disease. In this case, you should consider autosomal dominant polycystic kidney disease or autosomal dominant tubulointerstitial kidney disease.

Autosomal Dominant Polycystic Kidney Disease 4:33–4:47

Now, autosomal dominant polycystic kidney disease, or ADPKD, is caused by a mutation of the PKD1 or PKD2 genes, resulting in dysfunctional cilia and subsequent cyst development.

ADPKD 4:47–6:56

These patients typically report flank pain with or without hematuria, while the physical exam reveals elevated blood pressure, possibly with palpable kidneys.
Their labs will show elevated serum creatinine levels, as well as proteinuria and hematuria. Lastly, on ultrasound, you’ll see large kidneys with multiple cysts in the cortex and medulla.
With these findings, think of autosomal dominant polycystic kidney disease. Here’s a clinical pearl to keep in mind!
ADPKD commonly leads to end-stage renal disease requiring dialysis or kidney transplantation, as well as anemia, elevated blood pressure, and electrolyte imbalances.
Some patients are treated with a vasopressin receptor antagonist like tolvaptan, which slows the growth of kidney cysts when taken early in the course of the disease, reducing complications such as urinary tract infections, nephrolithiasis, and chronic flank pain.
If complications persist despite treatment, consider a nephrectomy. Extrarenal manifestations of ADPKD include liver and pancreatic cysts, diverticulosis, valvular heart disease, and cerebral berry aneurysms, which increase the risk of subarachnoid hemorrhage.
Here’s another important clinical pearl! Be sure not to mix up ADPKD with Autosomal recessive polycystic kidney disease, or ARPKD.
ARPKD is caused by a mutation in the PKHD1 gene and leads to renal failure in utero or in early childhood. Other common manifestations include oligohydramnios, pulmonary hypoplasia, growth impairment, recurrent cholangitis, and liver fibrosis leading to portal hypertension.
Finally, let’s discuss autosomal dominant tubulointerstitial kidney disease, or ADTKD, previously called medullary cystic kidney disease.

Autosomal Dominant Tubulointerstitial Kidney Disease 6:56–9:08

ADTKD is a genetic disorder characterized by renal tubular damage, interstitial fibrosis, and eventual glomerular sclerosis and renal failure.
Now, the tubular damage leads to sodium wasting and subsequent water loss, so these patients will typically report polyuria and polydipsia.
Additionally, there is reduced urate excretion, which can eventually result in urate crystal deposition in joints and gout.
Sometimes, your patient might even report a family history of gout. When it comes to the physical exam, it might reveal enlarged, painful joints.
Since there’s renal tubular damage, labs will show elevated serum creatinine and serum uric acid levels with normal urinalysis findings.
Finally, if the renal ultrasound shows small or normal-sized kidneys, sometimes with small cysts in the medulla, consider ADTKD.
Next, order genetic testing, and if it reveals a mutation in UMOD or MUC1 genes, that’s ADTKD. Here’s a high-yield fact!
Two autosomal dominant conditions that are often associated with the presence of renal cysts include Von Hippel-Lindau disease and tuberous sclerosis complex.
Von Hippel-Lindau disease is caused by a mutation in the VHL tumor suppressor gene, leading to widespread benign and malignant tumor formation.
Kidney cysts are usually premalignant, but over time they can progress into renal clear cell carcinoma. Other common sites of tumor formation include the central nervous system, blood vessels, adrenal glands, and pancreas.
On the other hand, tuberous sclerosis complex is associated with mutations in TSC1 or TSC2 tumor suppressor genes that result in the widespread development of hamartomas that can affect the kidneys, liver, heart, and even brain.
Additionally, these patients might develop benign renal cysts as well as renal cell carcinoma. Alright as a quick recap… Diagnosing cystic kidney disease requires a renal ultrasound, which typically reveals the presence of a single cyst or multiple cysts Patients without a family history of kidney disease might have either simple renal cysts, medullary sponge kidney disease, or acquired renal cystic disease.

Review 9:08–9:34

On the other hand, individuals with a positive family history of kidney disease might have autosomal dominant polycystic kidney disease or autosomal dominant tubulointerstitial kidney disease.