10. large animal med- equine urinary diseases

where/what is the anatomy of the left kidney in horses?

size: 18 x 10x 5 cm (H-W-D)

-17th rib space into paralumbar fossa

-medial to spleen

-palpable per rectum

where/what is the anatomy of the right kidney in horses?

size: 15 x 5 x 5cm (H-W-D)

-14th-17th rib space

-embedded in the lvier

-heart shape

-rarely palpable per rectum

what is the anatomy of the ureters in horses?

ureters are 6-8mm in diameter and embed in the bladder neck

can palpate if enlarged

how much urine can the adult equine bladder hold?

can hold 3-4L of urine before micturition prompted

how long is the urethra in mares vs in males?

mares: only 2-3cm long

male: 75-90cm long (no urethral diverticulum)

what sedation can you give male horses for penile relaxation in order to catheterize?

acepromazine +/- xylazine/detomidine

what are the regulatory functions of the kidney?

-water and electrolyte balance

-acid-base balance

-arterial pressure (renin production)

-red cell genesis (EPO production)

-active vitamin D production

what metabolic waste products/foreign chemicals are eliminated by the kidney?

-75-100% of urea excretion (produced by the liver)

-creatinine (from muscle)

-drugs or metabolites

-not bilirubin (if bilirubin is seen in the urine, it is conjugated, and likely due to cholestasis)

what are the signs of upper urinary disease in horses?

-polyuria

-discolored urine (can be upper or lower)

-weight loss

-colic (upper or obstruction)

-ventral edema (upper or lower)

-fever

-somnolence

-oral ulcerations

-dental tartar

what are the signs of lower urinary disease in horses?

-discolored urine (upper or lower)

-unusual micturition (frequency, posture, duration, vocalization, stream character)

-scalding or staining of hindlimbs and perineum

-ventral edema (upper or lower)

what history questions should be asked if suspicious of urinary disease?

-pollakiuria vs polyuria?

-urine color?

-record of water intake?

-other general findings: weight loss, lethargy, fever

what should be included in your physical exam if suspicious of urinary disease?

include palpation of bladder and left kidney

consider catheterizing if bladder is full

how can urine be collected for a urinalysis?

-catheterize urethra or specific ureter (for sterile collection)

-cystocentesis in foals only

-midstream free-catch

what is the normal USG of equine urine?

USG: 1.008-1.050 , >1.025 dehydrated

--> often <1.010 in foals

what are causes of red blood cells in the urine?

bladder stones

urethral rent (geldings/stallions)

idiopathic hematuria

neoplasia

pyelonephritis/cystitis

what are causes of hemoglobin in the urine?

intravascular hemolysis

what are causes of myoglobin in the urine?

rhabdomyolysis

how is hematuria differentiated from myoglobinuria and hemoglobinuria?

hematuria:

-urine centrifuges to a clear color with a pellet/clump of RBCs

-clear plasma

-low PCV/TP

how is myoglobinuria differentiated from hematuria and hemoglobinuria?

myoglobinuria:

-brown or red urine

-no change with centrifuging (bc myoglobin is a pigment)

-clear plasma

-high CK (>25kU/L)

-high TCO2 (chem)

how is hemaglobinuria differentiated from myoglobinuria and hematuria?

hemaglobinuria:

-urine doesnt clear with centrifuge

-pink plasma (bc intravascular hemolysis)

-dropping PCV

what CBC changes may be seen with urinary diseases in horses?

-increased neutrophils and fibrinogen, suggesting infection/inflammation

-mild anemia in chronic failure, if severe-suggests blood loss

-increased SAA (indicates inflammation)

what serum chemistry changes may be seen with urinary diseases in horses?

-azotemia (increased BUN and creatinine)

-hyponatremia (renal sodium/chloride) loss

-hyperkalemia (variable in horses)

-hypercalcemia (chronic renal failure, diet dependent)

how is renal azotemia differentiated from post-renal and pre-renal azotemia?

renal: >75% nephron loss, urine SG <1.020, and will have a poor response to treatment

what are signs of post-renal azotemia?

signs of urinary tract obstruction/disruption

how is pre-renal azotemia differentiated from renal azotemia?

evidence of fluid loss, USG> 1.020 pre-fluids

pre-renal azotemia improves rapidly, 30-50% decrease in 24 hours

how can ultrasound help diagnose urinary diseases in horses?

transabdominal (L and R) and per rectum (L)

U/S can determine size, architecture and can facilitate biopsy

how is the left kidney best imaged with ultrasound?

best imaged around 3.5MHz, with a macroconvex probe

medial to and less echogenic than spleen

how is the right kidney imaged with ultrasound?

in 14th-17th rib spaces

-more superficial than left kidney, in dorsal abdomen

what are benefits of transabdominal ultrasound when viewing the kidneys?

greater detail of the right vs left kidney

distinct cortex and medulla

what is the echogenicity of the kidneys?

medulla (darkest)--> cortex--> liver--> spleen (lightest)

what can be seen with per rectum ultrasound when viewing the urinary system?

gives good examination of left kidney and bladder

-the bladder has swirling echogenic sediment (normal)

-stones cast a round acoustic shadow, often seen in bladder neck at wrist depth

when is urinary endoscopy indicated?

-presence of dysuria/stranguria or pollakiuria

-abnormal bladder palpation/ultrasound

-hematuria

what is evaluated with urinary endoscopy?

evaluate for masses, stones, bleeding, and inflammation

-watch urine flow from each ureter

-small amounts every 20-30seconds, clear or yellow

-catheterize one or both ureters if needed

when is urine culture indicated?

when infection is possible

catheterized samples (sterile) preferable

when are renal biopsies indicated?

most useful for neoplasia and congenital disease (histopath); should be done via U/S guidance

limited information gain, cost and risk (hemorrhage)

when are bladder biopsies indicated?

for suspected neoplasia, intractable chronic cystitis

performed thru endoscope (mucosal pinch samples)

when is contrast radiography/CT indicated for urinary disease?

to identify ectopic or torn ureters in foals or minis

renal hypoplasia

what is acute renal insufficiency?

clinical syndrome of sudden decline in GFR, onset of azotemia and disturbed fluid, electrolyte and acid-base balances

what are causes of acute renal insufficiency?

usually from pre-renal or renal causes:

-toxic tubular nephrosis

-decreased renal perfusion (vasomotor nephropathy)

-obstruction or disruption of the urinary tract

-acute inflammation (interstitial nephritis)

-glomerulonephritis

-congenital dz (hypoplasia, dysplasia)

what are the most common causes of acute renal insufficiency?

toxic nephropathy and ischemic events

what renal toxins can cause acute renal insufficiency?

-aminogylcosides (gentamicin)

-hemoglobin, myoglobin

-NSAIDS (flunixin, bute/phenylbutazone, foricoxib)

-other drugs (oxytet, polymixin B, bisphos)

what are causes of renal ischemia, causing acute renal insufficiency?

-reduced cardiac output

-hemorrhage

-diarrhea

-sepsis

-endotoxemia

-long exercise

-complicated by NSAID effects on renal blood flow

how do aminoglycosides cause acute renal insufficiency?

affect proximal tubular epithelial cells

repeated administration more risk than dose (toxicity is cumulative- can occur after tx stops)

-concurrent risk factors (dehydration, diuretics, NSAIDs) also increase risk

what are clinical signs of acute renal insufficiency caused by aminoglycosides?

tubular casts (dead epithelial cells) in urine

increase in creatinine by 0.3mg/dL during treatment

how is renal aminoglycoside toxicity prevented?

-provide fluids during treatment

-prolong dosing interval until hydration is restored

-monitor serum creatinine +/- urinalysis

-judicious use of drugs that increase risk

-calcium supplementation (oral or IV)

what are causes of pigment nephropathy?

rhabdomyolysis or IV hemolysis

usually a concurrent exacerbating factor such as dehydration and/or nephrotoxic drugs

what are signs of pigment nephropathy?

may see abnormal colored urine, or

may not see discolored urine; intermittent color or pigment concentration too low to appreciate

how is pigment nephropathy treated?

involves identifying underlying cause and addressing it if feasible

-fluids until pigmentation ceases

-alkalinize urine (myoglobin)

-judicious use of NSAIDs

what drugs cause renal NSAID toxicity in horses?

-phenylbutazone “bute”

-flunixin

-ketoprofen

-aspirin

-firocoxib

toxicity is unusual in appropriatley dosed, hydrated horse**

--> NSAIDs increase risk of acute nephrosis in vasomotor cases

what pathologic changes to the kidney occur as a result of NSAID toxicity?

medullary crest necrosis (no azotemia)

-lower blood supply to this region exacerbated by NSAIDs

-subclinical, microscopic, or gross hematuria, normal function

-interstitial nephritis/nephrolithiasis with long term NSAID use

how is NSAID toxicity prevented?

-use appropriate dose and duration

-supplemental pain management

-monitoring hydration, chemistry, UA

what are the clinical signs of severe renal NSAID toxicity?

-anorexia/depression

-oliguria

-azotemia

-proteinemia (protein loss due to right dorsal colitis)

-azotemia

selective CO2 may reduce GI but not renal toxicity

horses with what condition commonly get vasomotor nephropathy?

with severe shock or endotoxemia

(from colic, diarrhea, acute blood loss, anesthesia)

what causes vasomotor nephropathy?

marked hypotension and vasoconstriction causing decreased renal perfusion and acute renal ischemia

-the renal medulla normally has low blood flow so is susceptible to ischemia and hypoxia

-cortex has high blood flow, so more susceptible to toxins

-disturbed auto-regulation is a prominent feature

what is the predominant lesion in vasomotor nephropathy?

tubular necrosis

can be exacerbated by nephrotoxic drugs (NSAIDs)

what are clinical signs of acute renal insufficiency?

-can be masked by primary disease

-dullness

-reduced feed/water intake

-dehydration

-inappropriately low urine volume after 6-12hr bolus

-changes in urine color depending on cause (pigmenturia, hematuria)

what chem panel changes are seen with acute renal insufficiency?

-azotemia

-hyponatremia/hypochloremia from renal loss

-+/- hyperkalemia (from anorexia, aldosterone release)

-azotemia that respond poorly to fluid therapy (bc is a renal azotemia)

what urinalysis changes are seen with acute renal insufficiency?

protein, casts, red cells, or other findings

USG <1.020

fraction sodium excretion >1% on pre-tx sample

what is seen on ultrasound with acute renal insufficiency?

-often unremarkable

-sometimes increased size or cortical echogenicity and enhanced corticomedullary distinction

what is the treatment for acute renal insufficiency?

-neutralize underlying cause

-correct fluid deficits in 6-12 hours (normal saline if low NaCL or LRS)--> 10-15% BW/day until azotemia improves

-correct electrolyte imbalances

-monitor azotemia, body weight, and urine output

-avoid nephrotoxic drugs

if a horse is oliguric after 10-12 hours or azotemia persists after treatment from acute renal insufficiency, what treatments could be considered?

-consider furosemide CRI (avoid in gentamicin toxicity)

-mannitol infusion (improves blood flow, GFR)

-dialysis (crude abdominal dialysis)

-dopamine

what is chronic renal insufficiency?

chronic insidious disease with gradual progressive loss of nephron function and/or population

over clinical signs once 75% of nephron mass lost

what are causes of glomerular disease leading to chronic renal insufficiency?

glomerulonephritis or amyloidosis

what are causes of tubulointerstitial disease leading to chronic renal insufficiency?

sequelae to acute tubular necrosis, pyelonephritis, nephrolithiasis, hydronephrosis, etc.

chronic interstitial nephritis with fibrosis most common

what congenital diseases may lead to chronic renal insufficiency?

renal dysplasia, hypoplasia

what is glomerulonephritis?

usually refers to immune-mediated injury:

-antigen-antibody complexes deposited along glomerular basement membrane

-thickens filtration barrier, decreases GFR

-might be a common cause of acquired CRF in horses

what urine protein: creatinine ratio is seen with glomerulonephritis?

>2:1

urine protein can falsely increase USG

what is tubulointerstitial disease?

'chronic interstitial nephritis'

-catch-all phrase for all non-glomerular causes of CRF

-about 40% of equine CRF cases

what is the cause of tubulointerstitial disease in horses?

usually a sequel to acute tubular nephritis following hemodynamic or toxic event

sometimes from chronic urinary obstruction or pyelonephritis

what is seen on histology with tubulointerstitial disease?

tubular damage + interstitial inflammatory cell infiltrate plus fibrosis if chronic

what are the different forms of congenital defects?

-renal agenesis

-hypoplasia/dysplasia

-polycystic kidney disease

when do urinary congenital defects become clinically apparent?

may not be apparent until later in life but be suspicious in horses <5 years old with renal dz of unknown cause

what are the clinical signs of chronic renal insufficiency?

-weight loss (most common)

-lethargy

-inappetence

-PU/PD

-mild ventral edema

-stunted growth (severe congenital defects)

-cardiac wall thickening due to chronic hypertension

how is chronic renal insufficiency diagnosed?

based on persistent isosthenuria with azotemia and clinical signs

other lab findings:

-high creat

-mild anemia/hypoalbuminemia

-hypercalcemia (unique to horses)

-glucosuria + proteinuria usually absent until P is terminal

what may be found on rectal examination of the urinary system with chronic renal insufficiency?

left kidney may be small and firm

obstruction or masses may be evident

what may be found on ultrasound of the urinary system with chronic renal insufficiency?

-loss of corticomedullary definition

-increased echogenicity

-decreased size

-may have nephroliths and hydronephrosis

what may be found with renal biopsy in cases of chronic renal insufficiency?

expect fibrosis and end-stage kidney disease

occasionally identify congenital dysplasia

what is the treatment for chronic renal insuffiency?

disease is usually advanced at diagnosis, so mostly managing symptoms:

-treat acute exacerbations with fluids

-access to free choice water and salt

-limit calcium intake

-adequate crude nutrition

-omega-3 fatty acid supplementation

-avoid nephrotoxic drugs

-monitor chemistry periodically

what is the prognosis for chronic renal insufficiency?

-longevity usually considerably decreased (light exercise to avoid fluid losses)

-supportive therapy may prolong life

-euth. based on weight loss, lethargy, and anorexia

is cystitis/pyelonephritis common in horses?

no, both dz's are rare in horses

can be primary or secondary but are most often secondary to stones, neoplasia, bladder paralysis, congenital defects, inflammation, or iatrogenic

what are the causative agents of cystitis/pyelonephritis in horses?

often gram-negative bacteria:

-e. coli, proteus, klebsiella, pseudomonas, enterobacter

-streptococcus, staphylococcus, coyrnebacterium (gram +)

foals: septic embolic nephritis (actinobacillus equuli)

what are the clinical signs of cystitis in horses?

pollakiuria

dribbling urine

painful urination

perineal scaling

-per rectum: thickened bladder

what are clinical signs of stones in the urinary tract?

-hematuria, especially after exercise

-pollakiuria

-dysuria, palpable stones

what are the clinical signs of pyelonephritis in horses?

all signs of cystitis plus:

-discolored urine (hematuria/pyuria)

-weight loss

-anorexia

-depression

-fever

-anemia

-per rectum: may feel large or painful kidneys, enlarged ureters

how is cystitis/pyelonephritis diagnosed?

-per rectum palpation and ultrasound findings

-urinalysis

-CBC

-endoscopy

what changes are seen on urinalysis with cystitis/pyelonephritis?

-increased WBCs, RBCs, protein

-bacteria in sediment

-positive urine culture

what CBC changes are seen with pyelonephritis?

increased WBC and fibrinogen

how can endoscopy be used to diagnose cystitis/pyelonephritis?

-identifies cystoliths, or anomalies of bladder mucosa

-evaluates urine flow from each ureter

-can catheterize each ureter thru scope for urine sample

what is the treatment for cystitis/pyelonephritis?

-eliminate cause if feasible

-abx based on culture and sensitivity and which achieve high urine concentrations

-severe pyelonephritis may require nephrectomy

which antibiotics and for what duration should cystitis/pyelonephritis be treated?

7-10 days for cystitis, 2-6 weeks for pyelonephritis

abx: TMS, ceftiofur, penicillin +/- aminoglycosides

what does urinary incontinence in adult horses usually reflect?

incontinence/sabulous urolithiasis usually reflects a primary neurologic disorder

what are neurologic causes of urinary incontinence in adult horses?

-equine herpes-1 virus myelitis

-EPM

-polyneuritis equi (cauda equina)

-illicit tail block

-sacral fracture, spinal neoplasia, osteomyelitis

-toxins: sorghum, sudan grass

what are non-neurologic causes of urinary incontinence in adult horses?

-bladder/urethral tumor

-calculi

-estrogen responsive (old mares)

-ectopic ureter (foals)

-dystocia/breeding injury

how is urinary incontinence diagnosed?

-PE and complete neuro exam

-bladder palpation: size, tone, ease of expression

-vaginal examination

-endoscopic examination

-spinal tap (for neuro dz)

-ultrasound

-urinalysis/culture

-CT/radiographic contrast

what therapy is used to manage urinary incontinence in adult horses?

-treat specific conditions (EPM, EHV-1)

-prevent urine retention and bladder distension

-prevent urine scald

-phenoxybenzamine reduces urethral resistance

-can try estradiol in older mares

-regular high-volume lavage if sabulous urolithiasis

what are the presenting complaints of urethral hemorrhage?

history of hematuria, especially end urination after clear stream. sometimes blood on back legs

typically stallions or geldings, quarter horses

what is urethral hemorrhage associated with in horses?

rents or tears in dorsal proximal urethra

how is urethral hemorrhage diagnosed?

via urethral endscopy

-rent or fistula in dorsocaudal urethra at ischial arch

-rule out hemorrhage from bladder and kidneys

what is the treatment for urethral hemorrhage?

medical: sexual rest, abx, NSAIDs/corticosteroids

surgical: incision of corpus spongiosum, laser rent, temporary urethrotomy

what is idiopathic renal hematuria?

sudden onset of gross hematuria arising from one or both kidneys with no identifiable cause

-arabians overrepresented

-usually no other clinical signs (unless severe blood loss causes signs of severe anemia)

-bleeding can be intermittent