Equine Urinary Medicine

Question 1

What are haemodynamic causes of acute renal failure?

Answer 1

– Hypovolaemia e.g. colitis, sweat, blood loss
– Volume redistribution e.g. effusions
– Decreased cardiac output
– Altered vascular resistance e.g. sepsis and endotoxaemia

Question 2

What are renal causes of acute renal failure?

Answer 2

• Primarily acute tubular necrosis secondary to ischaemia or nephrotoxin exposure
• Less commonly glomerulonephritis
  -e.g. immune mediated (EIA) or post-infection e.g. Strep. Equi
• or interstitial nephritis e.g. pyelonephritis

Question 3

How can ischaemia cause ARF?

Answer 3

• prolonged haemodynamic changes, renal infarction, NSAID administration
• large blood flow (20% cardiac output)
• Only 10 to 20% of blood flow to the kidneys reaches the medulla - more susceptible to ischaemic injury

Question 4

What are examples of nephrotoxins?

Answer 4

• antibiotics e.g. aminoglycosides (gentimicin), polymixin B,
  tetracyclines
• Endogenous substances e.g. haemoglobin and myoglobin
• Others e.g. NSAIDs, heavy metals

Question 5

What should be monitored on potentially nephrotoxic drugs?

Answer 5

• Serum Creatinine
  -treat aggressively if rises significantly

Question 6

How does aminoglycoside nephrotoxicity occur?

Answer 6

• Neomycin is the most nephrotoxic
  –gentamicin & amikacin similar
• Filtered by the glomerulus (no metabolism - all excreted by the kidneys)
• Reabsorbed by proximal tubular epithelial cells
• Accumulation in proximal tubular cells interferes with cells function
• Pre-treatment with calcium may reduce nephrotoxicity

Question 7

How does NSAID toxicity occur?

Answer 7

• Toxicity due to renal medullary crest and papillary necrosis and sloughing of the tubular epithelial cells in the kidneys
• Dose dependant effects
• Secondary to ischaemia 2ary to prostaglandin (PGE2 & PGI2 or COX 1) inhibition

Question 8

What are CS of nephrotoxicity?

Answer 8

• Usually referable to the primary problem
  –e.g. acute colic or colitis
• Anorexia and depression
  –Uraemia, fluid, electrolyte & acid-base disturbances
• May be just a worsening of the primary problem, or an apparent lack of response to therapy

Question 9

How is nephrotoxicity diagnosed?

Answer 9

• Hx, CS
• Urinalysis
• Serum Biochemistry - increased BUN + creatinine

Question 10

How do you treat nephrotoxicity?

Answer 10

• IV fluids to improve renal perfusion, correct metabolic disturbances + induce diuresis
  -replace loss + 2x maintenace if polyuric
• Discontinue nephrotoxic drugs
• Monitor BW, PCV, serum protein + biochem
• Poor prognosis if poor initial response to fluid therapy

Question 11

How do you treat nephrotoxic horse if oliguric?

Answer 11

• Furosemide (4x a day)
• Dopamine - renal vasodilator
  (synergistic)

Question 12

What are examples of chronic renal failure in horses?

Answer 12

• Glomerular disease is seen more as chronic vs. acute renal failure
• Acute tubular necrosis may progress to chronic interstitial nephritis
• Other acquired include renal neoplasia (e.g. adenocarcinoma, lymphoma), amyloidosis

Question 13

What are CS of chronic renal failure?

Answer 13

• Chronic weight loss
• Lethargy, poor hair coat, PU/PD, poor performance (mild anaemia)
• May see oral ulceration, gastroenteritis, excessive tartar and halitosis
• Ventral oedema inconsistent
  –hypoalbuminaemia relatively mild and offset by increase in globulins, except for glomerulonephritis

Question 14

How is Chronic renal failure diagnosed?

Answer 14

• Persistent isothenuria (1.008-1.014), with azotaemia + CS
• Mild anaemia + hypoalbuminaemia
• Electrolyte abnormalities =
  -hyperalcaemia
  -hypophosphataemia
  -hyponatremia
  -hypochloride
  -low bicarbonate

Question 15

What is treatment of chronic renal failure?

Answer 15

• Palliative
  -improve nutrition + lower protein
  -Decrease calcium (avoid alfalfa)
  -ensure water + salts always available
• if creatinine >800U/L = grave prognosis

Question 16

What is classed as PU/PD?

Answer 16

• PU = urine output >50ml/Kg/day
• PD = intake of more than 100ml/Kg/day
• Urine production + water consumption vary with = age, diet, workload, environmental temp

Question 17

What is Dysuria?

Answer 17

• Abnormal urination =
  -pollakiuria - more frequent
  -stranguria - difficulty urinating
  -haematuira
  -pyuria

Question 18

What are causes of PUPD?

Answer 18

• Renal failure
• PPID (Cushing’s disease)
• Primary or psychogenic polydipsia - most common
• Excessive salt consumption
• Diabetes insipidus
• Diabetes mellitus
• Sepsis and endotoxaemia
• Iatrogenic - fluid therapy

Question 19

What would you do to approach PUPD?

Answer 19

• CONFIRM!! =
  -complete blood count
  -serum biochem
  -Urinalysis = SG, glucose, protein
• Azotaemia + isosthenuria = chronic renal failure
• Azotaemia + hyposthenuria = recovery from acute renal failure
• Hyposthenuria without azotaemia = psychogenic polydipsia / Diabetes insipidus
• PPID = specific endocrine testing (ACTH)

Question 20

How can you distinguish between psychogenic polydipsia + Diabetes insipidus?

Answer 20

• Water deprivation test
  -do not perform in dehydrated horse
  -empty bladder + get baseline body weight
  -deprive from access to water
  -measure USG, BW + urea
• If USG increases = psychogenic polydipsia
  -If USG = hyposthenuric = diabetes insipidus

Question 21

How can you distinguish neurogenic + nephrogenic diabetes insipidus?

Answer 21

• Neurogenic = USG increases to >1.020 following ADH / vasopressin administration
• Nephrogenic = no change in USG after administration of ADH , vasopressin

Question 22

What is treatment of PUPD?

Answer 22

• Depends on primary cause =
• Psychogenic salt ingestion =
  -Prevent access to mineral salt
• Psychogenic polydipsia =
  -Environmental changes to relieve boredom
• Renal failure =
  -Allow constant access to water
  -Good diet
  -Avoid feeds rich in Ca (alfalfa)
• PPID =
  -Specific treatment: dopamine agonists (pergolide)
• Diabetes insipidus =
• Allow constant access to water
• Neurogenic = Vasopressin (short half life → impractical), Chlorpropamide, clofibrate → potentiate vasopressin action
  -Nephrogenic = Restrict Na intake, Thiazide

Question 23

What are 3 main causes of pigmenturia?

Answer 23

• Blood (haematuria)
• Haemoglobin
• Myoglobin

Question 24

How do you differentiate different causes of pigmenturia?

Answer 24

• Spin it down - if still red = haemoglobin / myoglobin
  -if not red = haematuria
• Blondheim Test (ammonium sulphate precipitation test)
• haemoglobin = haemolysed serum, haemolytic anaemia
• Myoglobin = serum biochem = increase CK + AST

Question 25

What are causes of myoglobinuira?

Answer 25

* Muscle cells rupture = * Rhabdomyolysis = –Sporadic/recurrent exertional rhabdomyolysis –Polysaccharide storage myopathy –Atypical myopathy –Post-anaesthetic myositis

Question 26

What causes haemoglobinuria?

Answer 26

* Haemolysis = –Immune mediated haemolytic anaemia –Neonatal isoerythrolysis –Infectious causes (Babesia, EIA...)

Question 27

How is haemoglobinuria diagnosed?

Answer 27

– Haemolysed serum – Anaemia (regenerative) – ↑ bilirubin – Assessment of blood film – Agglutination tests = Coombs test

Question 28

What are common causes of haematuria?

Answer 28

– Urinary tract infection - pyelonephritis / cystitis – Urolithiasis – Neoplasia

Question 29

What does timing of haematuria tell us?

Answer 29

* Throughout urination = -Kidneys -Ureters -Bladder * Start of urination = -Distal urethra * End of urination = -Proximal urethra and bladder neck

Question 30

What is seen with pyelonephritis? Dx? Tx?

Answer 30

* Ascending infections or consequence of septicaemia * Signs = haematuria or pyuria without stranguria or pollakiuria * Fever, weight loss, depression * Diagnosis = urinalysis (uretheral catheterization) + bacterial culture * Treatment = Prolonged antimicrobial course

Question 31

What is seen with cystitis? Dx? Tx?

Answer 31

* CS = haematuria or pyuria with stranguria or pollakiuria * Dx = urinalysis, cystoscopy, bacterial culture * Tx = Address primary cause + Antimicrobials

Question 32

What animals get urolithiasis? What are contributing factors? CS? Dx? Tx? Px?

Answer 32

* Males predisposed * >10years old * Lower urinary tract more common (60% bladder) * Contributing factors = Urine retention, UTI, genetic * CS = Haematuria, stanguria, pollakiuria, pyuira, incontinence, recurrent colic + loss of condition * Dx = Rectal palp bladder, US bladder, cystoscopy * Tx = Mares = manual removal -Stallions = laparocystotomy, lithotripsy * Px = decrease Ca in diet, urine acidifiers

Question 33

What is Sabulous cystitis? What causes it? Tx?

Answer 33

* Accumulation of crystalloid sediment in ventral bladder * Secondary to bladder paralysis / problems with bladder emptying = EHV-1, polyneuritis equi, sacral fractures * Tx = regular emptying + bladder lavage + control of 2ary UTI

Question 34

What are other causes of haematuria?

Answer 34

* Idiopathic renal haematuria = -Arab horse, Uni- or bilateral (unilateral more common) -Often severe enough to require blood transfusions -Tx = supportive; nephrectomy in severe cases * Exercise associated haematuria = -Typically microscopic, Due to bladder trauma against pelvis * Urethral defects = -Urethral rents or tears = Stallions and geldings -Haematuria at the end of urination -Dx = endoscopy → lesion on dorsal area of urethra at the level of the ischial arch -Tx = most resolve spontaneously; if persistent then perform temporary urethrostomy