nephrolithiasis

Question 1

What are the clinical signs and symptoms of nephrolithiasis?

Answer 1

Flank pain: Severe, colicky pain that radiates to the groin or lower abdomen.
Hematuria: Microscopic or gross hematuria.
Nausea and vomiting: Often associated with the pain.
Urinary urgency/frequency: If the stone is located in the lower urinary tract.
Fever/chills: Suggests concurrent infection (e.g., pyelonephritis).
CVA tenderness: Pain upon percussion of the costovertebral angle (CVA).
Absent peritoneal signs: Unlike gastrointestinal pathology, there is no guarding or rebound tenderness.

Question 2

What are the common medications that can cause kidney stones?

Answer 2

Loop Diuretics (e.g., furosemide): Promotes hypercalciuria, increasing the risk of calcium oxalate and calcium phosphate stones.

Acetazolamide: Causes alkaline urine, which can predispose to calcium phosphate stones.

Topiramate: Increases urinary pH and promotes calcium phosphate stone formation.

Protease Inhibitors (e.g., indinavir, atazanavir): Lead to formations poor solubility in urine.

Sulfa Drugs (e.g., sulfadiazine): Can precipitate as sulfa crystals in the urine, causing stones.

Uric Acid Increasing Agents: Medications that promote hyperuricemia (e.g., chemotherapy agents, thiazides) can cause uric acid stones.

Vitamin C (high doses): Metabolized to oxalate, contributing to calcium oxalate stone formation.

Vitamin D (excessive supplementation): Increases intestinal calcium absorption, leading to hypercalciuria.

Question 3

What is the most common type of kidney stone and its associated risk factors?

Answer 3

Calcium oxalate stones are the most common, associated with hypercalciuria, hyperoxaluria, low citrate levels, vitamin C toxicity, ethylene glycol, and disorders like inflammatory bowel disease (fat malabsorption).

Acidic pH (<5.5)

Question 4

How does Crohn’s disease increase the risk of nephrolithiasis?

Answer 4

Fat malabsorption in Crohn’s binds calcium, freeing oxalate for absorption, leading to hyperoxaluria and increased risk of calcium oxalate stones.

Question 5

What dietary modifications are recommended for preventing calcium oxalate stones?

Answer 5

Increase fluid intake (>2 L/day), maintain moderate calcium intake, reduce sodium and oxalate-rich foods (e.g., spinach, nuts), and consider citrate supplementation.

Question 6

What are the characteristic crystals seen in cystinuria?

Answer 6

Hexagonal crystals, which are indicative of cystine stones, commonly associated with an autosomal recessive genetic defect in amino acid reabsorption.

Highly acidic.

Treatment is surgical removal (staghorn calculi often require percutaneous nephrolithotomy).

Question 7

What is classically used to diagnose cystine stones?

Answer 7

Due to lucent (weakly opaque), requires a non contrast CT for diagnosis.
U/S can be used in pregnant women and children.

Nitroprusside Test: A qualitative test for cystinuria.
Positive Test: Turns purple when excess cystine is present in the urine.

Question 8

How are cystine stones managed?

Answer 8

Hydration: Increase fluid intake to at least 2.5-3 liters per day to reduce cystine concentration and promote stone prevention.

Urinary Alkalinization: Increase urine pH to >7.0 to improve cystine solubility
(medications: potassium citrate or sodium bicarbonate)

Cystine-Binding Thiol Drugs (for recurrent or refractory cases): Penicillamine or Tiopronin.

Dietary Modifications: Reduce methionine intake. Limit high-protein foods.

Regular urinalysis and 24-hour urine testing to monitor cystine levels and assess treatment efficacy.

Question 9

How are struvite stones formed, and what organisms are commonly implicated?

Answer 9

Struvite stones (magnesium ammonium phosphate) form in alkaline urine and are caused by urease-positive organisms, such as Proteus, Klebsiella, Serratia, Enterobacter, and Staphylococcus species.

Can develop into staghorn calculi.

Basic pH (>5.5)

Question 10

What is the hallmark finding of struvite stones on imaging?

Answer 10

Staghorn calculi, which fill the renal pelvis and calyces.

Question 11

What is the treatment approach for staghorn stones?

Answer 11

Staghorn stones: Managed with percutaneous nephrolithotomy.

Question 12

What are the risk factors for calcium phosphate stones?

Answer 12

Alkaline urine, hyperparathyroidism, and distal renal tubular acidosis (RTA 1).

Question 13

What are the risk factors for developing uric acid stones?

Answer 13

Hyperuricemia from gout, luquid tumors (leukemia), chemotherapy, low urine volume, acidic urine pH, dehydration (hot/arid climates).

Question 14

What are the features of nephrolithiasis due to uric acid stones, and how are they treated?

Answer 14

Features: Radiolucent stones on X-ray; detected on ultrasound or CT.

Treatment: Urine alkalinization with potassium citrate or sodium bicarbonate and allopurinol for hyperuricemia.

Question 15

What is the role of thiazide diuretics in preventing nephrolithiasis?

Answer 15

Thiazides reduce calcium excretion in the urine, helping prevent calcium-containing stones.

Question 16

What is the mechanism of action of potassium citrate in nephrolithiasis prevention?

Answer 16

Citrate binds calcium, reducing stone formation by preventing crystallization.

Question 17

What are the dietary recommendations for preventing calcium oxalate stones?

Answer 17

Increase fluid intake: >2 liters/day.

Moderate calcium intake (not low).

Reduce sodium and oxalate-rich foods (e.g., spinach, nuts).

Consider citrate supplementation.

Question 18

What is the initial imaging study for suspected nephrolithiasis?

Answer 18

Non-contrast CT scan of the abdomen and pelvis, as it has the highest sensitivity and specificity for detecting stones.

Question 19

What is the preferred initial imaging modality for diagnosing nephrolithiasis in children or pregnant patients?

Answer 19

Ultrasound, as it avoids radiation exposure, making it safer for children and during pregnancy.

Question 20

What is the first-line treatment for kidney stones ?

Answer 20

IV fluids.

Pain control: NSAIDs or opioids.

Question 21

Why are IV fluids critical in acute nephrolithiasis with AKI?

Answer 21

They help restore renal perfusion, promote diuresis, and prevent progression of acute kidney injury.

Question 22

What is the next step in management for nephrolithiasis with fever, leukocytosis, and AKI?

Answer 22

Aggressive IV hydration with isotonic solutions (e.g., lactated Ringer’s) and initiate antibiotics if infection is suspected.

Question 23

What size of kidney stones generally passes spontaneously, and what is the medical management?

Answer 23

<5 mm stones: Likely to pass on their own.

Medical management includes hydration, NSAIDs, and alpha-blockers (e.g., tamsulosin) or CCBs (nifedipine).

Between 5 and 10 mm monitor for spontaneous passage.

Question 24

What is the first-line pharmacologic treatment for facilitating passage of kidney stones <10 mm?

Answer 24

Alpha-blockers such as tamsulosin, which relax smooth muscle in the distal ureter.

Alternative medication is a CCB (nifedipine).

Question 25

In what instances would you use invasive interventions for a kidney stone?

Answer 25

AKI (elevated creatinine).

Infections.

Stones > 10 mm.

Question 26

What are the hallmark lab findings in acute nephrolithiasis complicated by infection?

Answer 26

Elevated WBC count (leukocytosis), fever, and possible AKI (elevated creatinine).

Urinalysis may show pyuria, hematuria, or bacteria.

Question 27

What are the invasive interventions for stones ?

Answer 27

Shockwave lithotripsy: Effective for stones in the renal pelvis or upper ureter but less effective for large or dense stones.

Ureteroscopy with holmium laser lithotripsy: Used for stones in the distal ureter or when other techniques are contraindicated.

Percutaneous nephrolithotomy: Preferred for very large stones, staghorn calculi, or septic patients with obstruction (plus antibiotics).

Question 28

What is the management of urinary stones >10 mm?

Answer 28

Stones >10 mm are unlikely to pass spontaneously, and early urological intervention is typically required. Alpha-blockers (e.g., tamsulosin) may be used to improve stone passage in selected cases before intervention but are mainly used as and adjunct. The patient will also obtain appropriate IV fluid and pain control, but the definitive treatment will be with an invasive intervention.

Question 29

What are the contraindications for shock wave lithotripsy (SWL)?

Answer 29

Pregnancy.

Stones in certain locations (e.g., distal ureter).

Question 30

What is the management for obstructive nephrolithiasis in a septic patient?

Answer 30

Emergency decompression with percutaneous nephrostomy or ureteral stent placement, along with IV antibiotics.