Nephrolithiasis

Question 1

SS - what is it and how to improve?

Answer 1

supersaturation: ratio of salt conc in urine to solubilities
SS>1 crystals can form and grow
can lower SS by increasing urine volume

Question 2

randall’s plaque hypothesis

Answer 2

a model for stone formation: crystals in urine become attached to a site of crystalline deposits of interstitial calcium phosphate after loss of normal urothelium –> fixed stone that grows over time

Question 3

geographical trends in stone

Answer 3

stone belt in US = southeast

- warmer temps + sunlight (increases urinary Ca++)

Question 4

most common type of stone

Answer 4

calcium oxalate = 80%

Question 5

causes of calcium oxalate stones

Answer 5

hypercalciuria - most common
hyperoxaluria: from increased production or absorption
hyperuricosuria: uric acid crystals
fam hx
dehydration
diet or meds: high protein, vit C and D, antacid abuse

Question 6

cause, pathophys, tx of enteric hyperoxaluria

Answer 6

cause: malabsorption syndromes (crohn’s disease, bypass)
pathophys: soaps bind ca in gut, more free oxalate to be absorbed
tx: PARADOXICAL Ca or Mg supplementation, tx underlying condition

Question 7

how does high protein diet lead to calcium oxalate stones

Answer 7

acid generation from AA metabolism –> bone buffering of acid –> hypercalciuria + acidic urine

Question 8

risk factors for calcium phosphate stones

Answer 8

hypercalciuria

alkaline urine: ex. distal RTA

Question 9

uric acid calculi pathogenesis

Answer 9

hyperuricosuria

persistently acidic, concentrated urine (decreases uric acid solubility)

Question 10

tx for uric acid stones

Answer 10

alkalinization of urine
fluid
tx underlying condition

Question 11

struvite stones - what are they and how do they form

Answer 11

supersaturation w/ magnesium-ammonium phosphate
form in presence of urinary tract infection w/ urea-splitting organism (proteus, klebsiella, serratia, enterobacter)
alkaline urine! - suspect strive if urine pH >8

Question 12

what type of stone is most common in women and paraplegics

Answer 12

struvite

Question 13

cystine calculi - cause and clinical features

Answer 13

cystinuria - genetic defect

clinical features: early onset in childhold or early adolescence, fam hx, progression to renal failure

Question 14

inhibitors of stone formation

Answer 14

deficiency can cause stones

• citrate: complexes w/ Ca++ to become soluble
• magnesium: complexes w/ oxalate to become soluble
• oral orthophosphate: decreases calcium absorption and excretion
• inorganic pyrophosphate

Question 15

tx of stones

Answer 15

80% symptomatic stones are ureteral and most of these will pass
10-15% req intervention
- shock wave tx
- percutaneous surgery
- endoscopic procedure

Question 16

tx of renal tubular acidosis

Answer 16

hydration
tx metabolic acidosis
increase citrate and K+: K-citrate

Question 17

tx struvite stones

Answer 17

antibiotics
urease inhibitors
percutaneous surgery
fluids, tx underlying disease

Question 18

cystine stone tx

Answer 18

high fluid intake
urine alkalinization
meds: d-penicillamine, alpha-MPG - disrupt disulfide bones in cysteine to increase solubility, but comes w/ SEs

Question 19

tx hypercalciuria

Answer 19

thiazide diuretic: blocks Na-Cl transporter in DCT –> increases Ca+ reabsorption

Question 20

pure Calcium phosphate stones - etiology

Answer 20

RTA

primary hyperparthyroidism