Kidney stones Flashcards
(3) Types of stones in urinary system
- nephrolithiasis (the formation of kidney stones)
- ureterolithiasis (the formation of stones in the ureters)
- cystolithiasis (the formation of bladder stones)
Who gets kidney stones?
- 10% of population (twice as common in males)
- recurrence rate: 10% at one yr, 50% at 5 yr, 60-80% lifetime
- peak incidence 30-50 yr of age
- 75% of stones
What are the risk factors for kidney stones?
- dehydration
- high dietary intake of animal protein, sodium, refined sugars, fructose
- underlying metabolic conditions
- Crohn’s disease
- Hypercalciuria
- low Mg2+ & citrate
• hereditary: RTA, G6PD, cystinuria, xanthinuria, oxaluria, etc.
• lifestyle: minimal fluid intake; excess vitamin C, oxalate, purines, calcium
• medications: loop diuretics (furosemide, bumetanide), acetazolamide, topiramate, and zonisamide
• medical conditions: UTI (with urea-splitting organisms), myeloproliferative disorders, IBD,
gout, DM, hypercalcemia disorders (hyperparathyroidism, tumour lysis syndrome, sarcoidosis,
histoplasmosis), obesity (BMI >30)
(5) Types of kidney stones
- calcium stones (most common)
- struvite stones
- uric acid stones
- cystine stones
- drug-induced stone disease
Causes of calcium stones
- 75% of renal calculi
- Low protein, low salt diet may prevent (c.f. low-calcium)
Etiology & Rx:
- Hyperparathyroidism - Treated surgically or with orthophosphates if the patient is not a surgical candidate
- Increased gut absorption of calcium - The most common identifiable cause of hypercalciuria, treated with calcium binders or thiazides plus potassium citrate
- Renal calcium leak - Treated with thiazide diuretics
- Renal phosphate leak - Treated with oral phosphate supplements
- Hyperuricosuria - Treated with allopurinol, low purine diet, or alkalinizing agents such as potassium citrate
- Hyperoxaluria - Treated with dietary oxalate restriction, oxalate binders, vitamin B-6, or orthophosphates
- Hypocitraturia - Treated with potassium citrate
- Hypomagnesuria - Treated with magnesium supplements
Which type of kidney stone is associated with chronic UTI?
Struvite stones
- Magnesium ammonium phosphate stones
15% of renal calculi
- Usual organisms include Proteus, Pseudomonas, and Klebsiella species. C.f. Escherichia coli is not capable of splitting urea and, therefore, is not associated with struvite stones.
- Urine pH is typically >7.
- Underlying anatomical abnormalities that predispose patients to recurrent kidney infections should be sought and corrected.
UTI does not resolve until stone is removed entirely.
Which type of kidney stone is associated with high purine intake or malignancy (due to rapid cell turnover)?
Uric acid stones
- 6% of renal calculi
- urine pH
What type of kidney stone is associated with intrinsic metabolic defect?
Cystine stones
- 2% of renal calculi
- an intrinsic metabolic defect resulting in failure of renal tubular reabsorption of cystine, ornithine, lysine, and arginine.
Rx: low methionine diet, binders such as penicillamine or a-mercaptopropionylglycine, large urinary volumes, or alkalinizing agents.
Which drugs may cause drug-induced kidney stone diseases?
Indinavir (antiretroviral/anti-HIV); atazanavir; guaifenesin; triamterene; silicate (overuse of antacids containing magnesium silicate); and sulfa drugs including sulfasalazine (for bowel inflammation, diarrhoea, rectal bleeding, abdo pain)
Px of kidney stones
severe waxing and waning pain radiating from flank to groin, testis, or tip of penis
writhing, never comfortable, nausea, vomiting, hematuria (90% microscopic), diaphoresis, tachycardia, tachypnea
if fever, r/o concurrent pyelonephritis and/or obstruction
What are indications for admission to hospital for kidney stones?
- Intractable pain
- Fever (suggests infection) or other evidence of pyelonephritis
- Single kidney with ureteral obstruction
- Bilateral obstructing stones
- Intractable vomiting
• Compromised renal function
Ix for kidney stones
• screening
- CBC -> elevated WBC in presence of fever suggests infection
- electrolytes, Cr, BUN -> to assess renal function
- urinalysis: R&M (WBCs, RBCs, crystals), C&S
• imaging
- non-contrast spiral CT (contrast will mask the stone due to both being white) is the study of choice
- abdominal ultrasound may demonstrate stone or hydronephrosis (consider in females of child bearing age)
- abdominal x-ray will identify large radiopaque stones (calcium, struvite, and cystine stones) but may miss smaller stones, uric acid stones or stones overlying bony structures. Consider as an initial investigation in patients who have a history of radiopaque stones and similar episodes of acute flank pain (CT necessary if film is negative)
• strain all urine -> stone analysis
DDx of kidney stones
- acute ureteric obstruction
- acute abdomen: biliary, bowel, pancreas, AAA
- gynecological: ectopic pregnancy, torsion/rupture of ovarian cyst
- pyelonephritis (fever, chills, pyuria, vomiting)
- radiculitis (L1): herpes zoster, nerve root compression
Acute Rx for kidney stones
• medical
- analgesic ± antiemetic
- NSAIDs help lower intra-ureteral pressure
- medical expulsion therapy (MET)
○ α-blockers: increase rate of spontaneous passage in distal ureteral stones
○ calcium channel blockers
- ± Abx for bacteriuria
- IV fluids if vomiting (note: IV fluids do NOT promote stone passage)
• interventional:
- required if obstruction endangers patient, e.g. sepsis, renal failure
- first line: ureteric stent (via cystoscopy)
- second line: image-guided percutaneous nephrostomy
Elective (not acute) Rx for kidney stones
○ may stent prior to ESWL if stone is 1.5-2.5 cm
○ ESWL (extracorporeal sound wave lithotripsy) if stone 2 cm (see sidebar)
conservative if ureteral stone
