Canine urolithiasis Flashcards
Predisposing and risk factors
- small breeds > large breeds
- gender
- diet and water consumption
- increased Ca excretion (drugs, systemic disorders)
- defects in purine metabolism
Diet and water consumption that predisposes to struvite formation
increased Mg, P
decreased water consumption
Diet and water consumption that predisposes to calcium oxalate formation
dry acidifying diet
increased Ca, oxalate, vit C
decreased water consumption
Diet consumption that predisposes to ammonium urate formation
increased purines (endogenous or exogenous)
Drugs that predispose to stone formation (increase Ca excretion)
urinary acidifiers
furosemide
glucocorticoids
Systemic disorders that predispose to stone formation (increase Ca excretion)
- hypercalcemia: primary hyperparathyroidism (dogs), idiopathic hypercalcemia (cats)
- Cushing’s disease (hyperadrenocorticism): glucocorticosteroids (increase mobilization of Ca from bone, decrease tubular re-absorption of Ca)
Predisposing and risk factors of Ammonium urate uroliths
- portal vascular abnormalities
- hepatic dysfunction
- being a dalmation
Predisposing and risk factors of Xanthine uroliths
long term treatment with allopurinol
Diagnosis criteria
- incontinence, dysuria, pollakiuria, anuria, hematuria
- secondary microbial UTI (defective local host defense, foreign bodies in urinary tract)
- palpation
- rads or u/s
- urinalysis: sediment (pyuria, hematuria, bacteria, crystals), pH, specific gravity
- quantitative analysis
Crystalluria
- it likely proceeds urolith formation, BUT not all animals with crystalluria form uroliths
- uroliths can be present without crystalluria
- type of crystal does not always relate to type of urolith
Oversaturation
- unstable soln
- crystals spontaneously precipitate (homogenous nucleation)
- crystals aggregate and grow
- crystals do not dissolve
Supersaturation
- metastable soln
- crystals do not spontaneously precipitate; precipitate on templates (heterogenous nucleation)
- crystals may aggregate
- inhibitors will impede or prevent crystallization
- crystals do not dissolve
Undersaturation
- stable soln
- crystals do not precipitate
- crystals do not aggregate or grow
- crystals dissolve
Urolith formation
- urinary retention
- decreased concentration of crystallization inhibitors (for Ca oxalate inhibitors include: Mg, citrate, nephrocalcin, glycosaminoglycans)
- once nucleation has occurred, crystal growth may occur at lesser degrees of supersaturation (metastable soln)
- temperature change after urine collection induces crystal precipitation (so need to check for crystals in house)
A single diet can be formulated to be
undersaturated for struvite (treatment and prevention) and metastable for Ca oxalate (prevention)
Composition of struvites
Mg, NH4, PO4, occasionally Ca
Gross appearance of struvites
white to yellow, soft or hard, smooth or rough
Type specific characteristics of struvites
radiodense and form in alkaline urine
Gender, Age, concurrent disease, breed prevalence for struvites
- female, 85-95% prevalence
- 1-8 yrs (young adults)
- UTI in 2/3 cases (infection induced struvite vs sterile struvite[sometimes in dogs but more often in cats])
- mini schnauzer, bichon, shih tzu, mini poodle, lhasa apso (small breeds are commonly affected)
Struvite formation
- low water consumption, low urine volume
- alkline pH
- diet (directly relates to urine conc of Mg, PO4, [Ca])
- urea (NH4 conc related to dietary protein)
- disease (UTI- urease producing bacteria, staph, proteus)
Dietary management of struvites (dissolution)
- promote diuresis (urine SG <20%)
- add dietary Na
- acidify urine (pH 5.5-6.) with calculolytic diet (feed for 1 m after negative rads), supplemental acidifiers (dl-methionine or NH4Chloride)
- control UTI (give abx as long as uroliths can be seen by rads, do not give abx if sterile struvites)
Time for dissolution of urocystoliths (struvites)
- literature says mean of 3.5 months (8-20 wks), but may see dissolution in 3-4 wks
Time for dissolution of nephroliths (struvite)
- 67-300 days, mean 184 days
use pH to help make educated guess, recheck in 2-3 wks to see if any changes in site in rads
Precautions with calculolytic foods
- increased NaCl concentration (caution with patients with CHF, CRF, hypertension)
- patients at risk for pancreatitis (low protein/high fat diet)
- protein levels too low for immature dogs, gestation, lactation (feed no longer than 2 wks)
Prevention of struvites
- prevent UTI! The diet will not prevent struvite urolithiasis if infection with a urease producing microbe is present
- promote diuresis
- ensure appropriate energy level
- for sterile struvite: change diet composition and feeding patterns, +/- acidifiers to maintain urine pH 6.2-6.4
Does the size of stones affect the length of time for dissolution
NO
Composition of ammonium urate
NH4 and uric acid
Gross appearance of ammonium urate
small, brittle, brown to green, concentric laminar rings on cross section
Type specific characteristics of ammonium urate
radiolucent (will “hide” in rads)
form in acidic urine
Gender, age, concurrent disease of ammonium urate
- male (>85%)
- <1 yr with portosystemic shunts (PSS), mean 3.5 yrs without PSS
- PSS, liver disease, +/- UTI
Breed predisposition for ammonium urate
- dalmatian: only 30-40% of uric acid becomes allantoin, increased serum and urine levels of uric acid, autosomal recessive inherited possibly
- english bulldog
- mini schnauzers and yorkies b/c of PSS
Ammonium urate formation
- high urinary conc of urate (urate comes from monobasic ammonium salt of uric acid)
- excess purines: oxypurines- hypoxanthine, xanthine, uric acid; aminopurines- (endogenous) adenine, guanine; methylpurines- caffeine, theophylline, theobromine
- high urinary ammonium
Dissolution of ammonium urate uroliths
- promote diuresis
- control UTI (when present)
- restrict dietary protein (10-18%), purine
- maintain a neutral - alkaline urine (pH 7.1-7.7), can give potassium citrate with meals if urine isn’t consistently alkaline
- treat with xanthine oxidase inhibitor if urate excretion is >10 mg/kg/day
- allopurinal (10-15 mg/kg) + purine restricted diet to minimize risk of xanthine stone formation
Time for dissolution of ammonium urate
4-40 wks (mean 14.2 wks)
success rate 40%
Prevention of ammonium urate
- PSS surgery
- feed low purine diet that promotes the formation of dilute alkaline urine (these diets are not appropriate for growth, lactation, gestation; high fat)
- avoid acidifying high protein diets (these lead to excretion of amonium ions)
- monitor daily urate excretion (goal is to have it reduced by 1/2 of pretreatment values)
Composition of calcium oxalate stones
Ca and oxalic acid
Gross appearance of calcium oxalates
small, hard, brittle, cream to tan to brown-green, smooth or sharp edged
Type specific characteristics of calcium oxalates
radiodense (more than struvites, almost same as bone)
can form in slightly acidic to neutral urine
Gender, age, breed predisposition for calcium oxaltes
- males (>70%)
- 6-12 yrs
- mini schnauzer, lhasa apso, shih tzu, yorkies, mini poodle
Calcium oxalate formation
- calculogenic minerals do not = crystallization inhibitors
- hypercalciuria: intestinal Ca hyperabsorption (believed to be cause in mini schnauzers), renal leak, excessive skeletal mobilization of Ca (resorptive)
- hyperoxaluria: diet oxalates (veggie or grain sources), ascorbic acid, amino acids (glycine, serine), restriction of dietary Ca (increased GI oxalate absorption, so need to control levels of Ca and oxalate)
- crystallization inhibitors: from soluble salts with Ca and oxalic acid (citrate, Mg, pyrophosphate), interfere with binding of Ca and oxalic acid (tamm-horsfall glycoprotein, nephrocalcin)
Calcium oxalate prevention
- cannot be dissolved!
- reduce urine Ca and oxalate conc
- avoid excessive dietary oxalates, vit C and D
- restrict dietary protein (10-18%)
- maintain adequate (moderate) dietary Ca (restriction increases intestinal absorption and urinary excretion of oxalate)
- do NOT restrict P, this would increase Ca absorption
Potassium citrate for prevention of calcium oxalates
- through diet
- urocit-K or polycitra-k at 50-150 mg/kg q 12 hrs
- acts to sequester Ca from oxalate (Ca binds to citrate, Ca citrate is more soluble)
- alkanalizes urine pH
Thiazide diuretic for prevention of calcium oxalates
- increases Ca resorption in proximal tubules
- hydrochlorthiazide at 2-4 mg/kg q 12 hrs for 2 wks
Things that dietary management of calcium oxalate promotes
- high concentration and activity of urolith inhibitors (avoid significant aciduria)
- dilute urine: maintain SG<1.020, canned diet, add water to dry food, adding NaCl to food (not indicated in patients with CRF, cardiovascular dz)
Cystine urolithiasis
- cystinuria is an inborn error of metabolism
- breeds: english bulldog, dachshund, basset hound, newfoundland
- age: 2-5 yrs
- radiodense
- forms in acidic urine and becomes relatively soluble in alkaline urine
Cystine urolithiasis dietary management and therapy
- reduce dietary protein
- promote diuresis (urine SG<1.020)
- feed alkanalizing diet (potassium citrate, sustain pH ~7.5)
- start with foods before adding drugs
- thiol-containing drugs: d-penicillamine, N-(2-mercaptopropionyl)-glycine
