Posted by Crohn on September 01, 2009 at 18:31:39:
(71.93.223.242) on September 01, 2009 at 18:31:39:
why oxalate stones in Crohn's?
okt3 - 09/01/09 12:27
step1 and step2 UW but I got the expl. from step2 UW
A 32-year-old male presents with recurrent abdominal pain. A small bowel study
reveals several strictures in the small bowel. He was diagnosed with Crohn's
disease. He underwent a small bowel resection. Two months later, he presents
with colicky left flank pain with mild hematuria. He was admitted and IV hydration
was given. An IVP shows a kidney stone. The type of kidney stone that occurs
after resection of small bowel is:
A. Calcium phosphate
B. Oxalate
C. Struvite
D. Urate
E. Cystine
Explanation:
Oxalate stones are due to excessive GI absorption of oxalate. Hyperoxaluria
occurs in patients with small bowel resection, inflammatory bowel disease and
other malabsorptive states. The increased intestinal fat binds dietary calcium,
which is then unavailable to bind oxalate as usual. Therefore, increased oxalate
absorption in large bowel (unabsorbed bile salts may aid this) occurs and
precipitates in the kidney. Increased oxalate can also occur in people who drink
large amounts of tea, coffee, beer, chocolate and ethylene glycol overdose.
Choice A: Calcium phosphate stones are associated with hypercalciuria.
Conditions that may cause hypercalcemia are sarcoidosis, immobilization,
Cushing syndrome, and renal tubular acidosis. Standard treatment of calcium
stone is to increase fluid intake and use of thiazide diuretics. Note that Lasix
(Furosemide) should not be administered as it may precipitate calcium stones.
Choice C: Struvite stones form in the collecting system and become infected with
urea splitting organisms. Conditions required for formation of struvite stones are
presence of high urine pH, magnesium, ammonium and carbonate levels.
Choice D: Uric acid stones occur when urine is saturated with uric acid in the
presence of an acidic urine and dehydration. Urate stones occur in patients with
gout, myeloproliferative disorders and diarrhea. Treatment is with fluids,
alkalinization of urine and allopurinol.
Choice E: Cystine stones are rare and occur as part of a rare inherited disorder of
defective renal transport resulting in over-excretion of cystine. Stone formation
begins in childhood and are a rare cause of staghorn calculi.
Educational objective:
In a patient who undergoes bowel resection and then develops kidney stones, one
should always suspect oxalate as the culprit.