SA Clinical Nutrition 2

Question 1

1. Crystals vs uroliths.
2. Define crystalluria.

Answer 1

1. Urolith = urinary stone = macroscopic.
   - organised crystal aggregates of minerals in small amounts of organic matrix.
   Crystal = microscopic mineral precipitate.
   Crystalluria and uroliths may happen separately or together.
   - NOT necessarily the same constituents.
2. Crystals in the urine.

Question 2

Urolith formation process.

Answer 2

Urine subsaturated - no crystals.
Solubility product (Ksp) - urine saturated with a compound.
Urine supersaturated.
- inhibitors of crystal formation in urine enables holding compound in solution.
Formation product (Kf) - crystals form as compound precipitates out.
Urolith formation can occur.

Question 3

1. Promotors of crystal formation.
2. Types of urolith formation.

Answer 3

1. Compound concentration increase in the urine.
   Increased USG.
   Urine pH.
   Urine stasis - low frequency of voiding.
2. Homogenous (pure).
   Heterogenous.
   - crystal starts to form a stone, or aggregates of crystals form a stone on a central nidus of material e.g. inflammatory material, a different crystal.
   - requires less saturation.

Question 4

General rules for urolith management.

Answer 4

Crystalluria frequently normal, asymptomatic and does not need treatment.
- some crystal types abnormal and require investigation / management.
Uroliths frequently symptomatic need treatment:
- local inflammation.
- secondary infections.
- obstructions.
Uroliths MAY be asymptomatic
- may not need treatment.
– e.g. asymptomatic non-dissolvable uroliths without obstruction risk.

Question 5

Symptomatic lower urinary uroliths.

Answer 5

Urethroliths lead to obstruction.
- unproductive urination.
Cystoliths lead to cystitis signs.
- +/- bacterial cystitis.
- may also be asymptomatic.

Question 6

Symptomatic upper urinary uroliths.

Answer 6

Nephroliths:
- abdominal pain, anorexia / inappetence, lethargy.
- +/- pyelonephritis.
- may also be symptomatic.
Ureteroliths:
- cats.
- may present like AKI.
- may present like CKD.
- image every patient with renal/post-renal azotaemia.
- may also be asymptomatic.

Question 7

Ureteroliths clinical presentation.

Answer 7

Unilateral obstructions may not be azotemic.
- depends on reserve in non-obstructed kidney.
‘Big kidney, little kidney’.
- little = CKD on non-blocked side.
- big = renal swelling / renomegaly on blocked side.
Consider possibility in ANY abdominal pain or inappetent cat.
- much less common in dogs.

Question 8

Addressing symptomatic uroliths.

Answer 8

Stabilise patient and any hyperkalaemia medically beforehand.
If obstructed, identify site of obstruction.
- Urethra:
– retropulsion of stone into the bladder and remove via cystotomy.
– urethrotomy rarely needed.
–> seek referral if needed.
- Ureter:
– intervention/bypass (referral).
If non-obstructive, in either:
- bladder (cystoliths):
– amenable to dissolution.
–> medical.
– not amenable to dissolution.
–> cystotomy vs minimally invasive techniques e.g. voiding urohydropropulsion / laser therapy w/ cystoscopy.
- kidneys (nephroliths):
– dissolution of nephroliths possible.
– if symptomatic and dissolution not possible –> seek referral advice re. management options.
–> surgical removal.
–> extracorporeal shockwave lithotripsy.

Question 9

Longer term urolith management.

Answer 9

Patients are stone formers.
- need longer term management.
– some type have predisposing cause, which can be addressed and the patient should not form stones longer term.
Classify stone composition.
- different stones need different management.
Ideally submit for analysis.
- otherwise best guess = signalment, radiopacity, urine pH, underlying disease/predispositions.
Always elucidate pathogenesis where possible.
- underlying disease?
- a concurrent UTI?

Question 10

1. Moderate-markedly radiopaque stones on radiograph.
2. Moderately radiolucent stones on radiograph.
3. What size do uroliths need to be to visualise on radiograph?
4. Uroliths on radiographs.

Answer 10

1. Calcium oxalate (more common), struvite (more common), calcium phosphate, silica.
2. Urate (more common), cystine, xanthine.
   *N.B. stones may become more opaque as they get larger.
3. > 2-3mm big.
4. Plain:
   - radiopaque ‘liths.
   Contrast/double contrast:
   - radiolucent ‘lith.

Question 11

Ultrasonography.

Answer 11

Operator dependent.
Can visualise radio-opaque and radiolucent ‘liths.
Useful for evaluating renal pelvic dilation due to fluid accumulation.
- used as an indicator of ureteric obstruction.

Question 12

Urinalysis.

Answer 12

USG - concentrated urine : risk of supersaturation.
pH - may guide likely stone type.
Protein - often increased
– urothelial inflammation.
Blood? Inflammatory cells?
- direct urothelial inflammation from urolith.
- +/- concurrent UTI.
Sediment exam - crystalluria?
– analyse fresh.
– may NOT be concordant with the urolith.
Culture.

Question 13

How can urine pH help to identify what crystals are present?

Answer 13

Acidic pH = urate (most common), cystine, xanthine, calcium phosphate (brushite).
Acidic to neutral = calcium oxalate (most common), silica.
Alkaline to neutral = calcium phosphate (hydroxyapatite).
Alkaline pH = struvite.

Question 14

General principles of urolith management.

Answer 14

Dilute urine = supersaturation not possible.
- increase water intake.
– multiple/variable water sources.
– wet diet +/- added water.
- Target USG:
– cats <1.030.
– dogs <1.020.
Encourage voiding.
Avoid obesity.
SPECIFIC management will depend upon stone type.

Question 15

Uroliths in dogs.

Answer 15

Struvite most common.
- infection associated.
Calcium oxalate.
Urate.
Other types.
Cystoliths (bladder) and urethroliths (urethra) most common sites.

Question 16

Uroliths in cats.

Answer 16

Struvite most common (from analysis of stones removed from the LUT).
- calcium oxalate most common in upper UT.
Other types too.
Increased incidence of ureteroliths and nephroliths so represent as AKI +/or CKD.