TOPIC 13: Nephrolithiasis

Question 1

what is nephrolithiasis? what are the different types of stones? (4)

Answer 1

calculus formation at any level in the urinary collecting system, most often then arise in the kidney.

types:

1) calcium oxalate or CO mixed with calcium phosphate -radiopaque (80%)
2) magnesium ammonium phosphate- radiopaque (10%)
3) uric acid-radiolucent (7%)
4) cystine stones-radiopaque (1-2%)

Question 2

Etiology of kidney stones (3)

Answer 2

requires a confluence of predisposing factors:

1) concentration of the solute-the most important cause is increased conc of the stone’s constituents so that it extends their solubility in urine (supersaturation)
2) urine pH
3) bacterial infections

Question 3

calcium stones (6 causes)

Answer 3

pts who develop calcium stones have hypercaluria that may or may not be associated with hypercalcemia

1) idiopathic
2) hyperaldosteronism
3) hypercalcemia
4) Renal tubular acidosis
5) drugs (VITD)
6) diet

Question 4

struvite stones (cause)

Answer 4

magnesium ammonium phosphate

• occur in pts with persistently alkaline urine resulting from UTIs
• particularly urea splitting bacteria : proteus vulgaris, staphylococci

Question 5

uric acid stones (2 causes)

Answer 5

1) diseases that involve rapid cell turnover: gout, leukemias
2) purine rich diets

Question 6

cystine stones (cause)

Answer 6

associated with a genetically determined defect in the renal transport of certain amino acids including cysteine.

Question 7

prevention of kidney stones

Answer 7

1) increase urine output to >2000ml/day
2) diet (avoid purine rich food)
3) thiazide diuretics
4) allopurinol (inhibits uric acid formation because it blocks xanthine oxidase, used to treat gout)
5) pyridoxine -vit B6- (for primary hyperoxaluria)
6) urinary alkalization( uric acid or cysteine stones)
7) antibiotics (stuvite stones)
8) acetohydroxamic acids( inhibits urease)
9) captopril, penicillamine, thioproline( cysteine stones)