Urolithiasis Part 3

Question 1

describe calcium oxalate urolithiasis

Answer 1

signalment:
-middle-aged to older
-long haired cats
-small dogs
-outliers: form stones at very young age (bichons), siamese and ragdolls also at young age
-dogs: males > females
-cats: males = females

blood work: usually normal, or hypercalcemia (causes them to pee calcium out into urine and form stones)

urinalysis:
-acidic
-crystals in less than 50%

radiography:
-multiple
-dense, round, irregular

Question 2

describe hypercalcemia causes (HOGS IN YARD)

Answer 2

Hyperparathyroidism (primary or nutritional), hyperadrenocorticism
Osteolysis
Granulomatous disease
Spurious

Idiopathic
Neoplasia

Youth
Addison’s, vitamin A
Renal
D vitamin toxicosis

Question 3

what is the ONE most common cause of hypercalcemia in cats associated with calcium oxalate urolith formation? what about dogs?

Answer 3

cats: idiopathic

dogs: neoplasia (lymphoma) is hypercalcemia alone, but hyperparathyroidism and hyperadrenocorticism are associated with stones!!!

takes MONTHS for CaOx stones to form
-why neoplastic dogs die before get stones

Question 4

describe urine calcium/urine creatinine

Answer 4

shows that stone formers (in vet med) tend to have higher levels of calcium in urine (so treat CaOx stones by trying to lower calcium concentration in urine)

Question 5

how do we handle CaOx stones?

Answer 5

CANNOT dissolve them!! (which sucks because they’re so common)- require physical, more invasive, removal

Question 6

describe nephroureteroliths

Answer 6

1. not associated with progression of CKD
2. intervene IF:
   -obstruction to urine flow
   -grow in face of appropriate therapy
   -associated with infections, pain, or serious hematuria
3. clinical signs:
   -usually incidental finding during CKD screening
   -don’t show big signs like humans!
   -may cause urine color change (if see in absence of LUT signs, go looking for kidney stones)
   -suspicious if stable CKD cat suddenly becomes UNSTABLE
4. big kidney, little kidney:
   -bigger kidney more functional (still in hypertrophy stage) so is more prone to stone formation
5. clinicopathlogic findings:
   -associated with CKD, but not its progression
   -+/- UTIs: 33% cats, 77% dogs (Bartges doesn’t see)
   -hypercalcemia
6. diagnosis:
   -radiography: big kidney, little kidney, stones; but if colon full of mienral-dense poop may not be able to see
   -ultrasound: look for dilated ureter, stone in ureter, acoustic shadow/comet tail from stone, twinkle artifact on color flow doppler
   -excretory urography (contrast study):
   -CT is great! don’t even need contrast, stones are very dense

Question 7

describe medical management of nephroureteroliths

Answer 7

1. NOT if oliguria, hyperkalemia, or progression over/within 24-72 hours
   -need surgical management
2. treatment: goal is to fill kidneys with so much fluid that can push out stones (medical expulsion therapy)
   -NOTE: usually CKD cats prone to hypertension so be careful of that! and also of fluid overload!! (see other for more info)
3. surgical management:
   -nephrectomy (a shame, per Dr. Bartges) unless ALL nephrons gone

-nephrotomy: cut into kidney down to pelvis and scoop stone out (cutting through arcuate artery so if do with cat in CKD, WILL affect function; avoid if possible)

-pyelolithotomy/proximal ureterotomy: not cutting through vessels and tissue

-lithotripsy: try to use shockwaves to break up, works well in dogs, not so much in cats bc tiny tiny ureters (works great in people bc larger ureters)

-ureterotomy, neoureterocystotomy, nephrocystopexy

5. if very very sick, try hemodialysis

Question 8

when should a ureteral obstruction be monitored rather than decompressed?

Answer 8

if renal pelvis is >5mm dilated decompress

if no evidence of dilation, take a less invasive approach

Question 9

describe medical expulsion therapy

Answer 9

1. IV fluids
2. mannitol 20%
3. amitriptyline:
   -facilitates passage of urethral plugs
4. alpha blockers: ureteral contraction
   -prazosin, tamsulosin
5. +/- anti-inflammatories?
   -prednisone, dexamethasone, NSAIDs? (could make kidneys worse)

Question 10

describe interventional options for kidney stones

Answer 10

1. stents!
   -double pigtail stent (place scope or surgically)
2. place a SUB (alternate route around ureter, urine takes path of least resistance)

Question 11

describe post-obstruction relief/care

Answer 11

1. fluid therapy is VITAL: post-obstructive diuresis
   -will pee a lot
2. electrolytes: to avoid hypokalemia
3. acid-base care/monitoring: avoid metabolic acidosis
4. clinical signs of uremia: anemia, analgesia, nutrition

Question 12

describe prognosis of kidney stones

Answer 12

1. surgically managed cases: if survive 1st month, great survival rate
2. medically managed cases: if survive 1st month, lower survival rate than surgical

Question 13

describe pseudorecurrence

Answer 13

accidentally leaving a stone in

Question 14

describe stone prevention in cats

Answer 14

1. many are hypercalcemic, so monitor and control calcium
   -if identifiable disease: treat if can
   -if not: high fiber diet, potassium citrate
2. normocalcemic:
   -dietary modification: oxalate preventative diet: moderate protein, moderate to low calcium, neutral to alkalinizing, diuresis, +/- higher fiber

Question 15

describe canine calcium oxalate diet

Answer 15

moderate protein, moderate to low calcium, neutral to alkaline pH, diuresing, +/- fiber

Question 16

describe thiazide diuretics for calcium oxalate

Answer 16

1. act on distal convoluted tubule
2. promotes Na+ excretion and diuresis BUT also reduces the amount of calcium in the urine by increasing reabsorption in serum
3. so DONT use with hypercalcemic cats!!!
4. decreases calcium in urine which is helpful if not a hypercalcemic cat

can also use potassium citrate, bisphosphonates, bitamin B6, and glucocorticoids for calcium oxalate