Download bacterial pyelonephritis

BACTERIAL PYELONEPHRITIS
Jennifer Good, DVM
Resident, Emergency and Critical Care
Mark P. Rondeau, DVM, DACVIM (SAIM)
Staff Veterinarian
Department of Clinical Studies
Matthew J. Ryan Veterinary Hospital of the University of Pennsylvania
Douglass K. Macintire, DVM, MS, DACVIM, DACVECC
Professor
Department of Clinical Sciences
Auburn University
P
yelonephritis is an inflammation of the renal
parenchyma and renal pelvis that may be acute
or chronic. The terms acute and chronic refer to
the nature of the host response rather than the duration
of inflammation. Most cases of pyelonephritis in dogs
and cats are caused by bacterial infection. Bacterial
pyelonephritis is most often caused by ascending urinary tract infection (UTI); however, hematogenous
spread is also possible. Disruption of local mechanical
or immunologic defense mechanisms in the urinary
tract is fundamental to the development of most cases
of canine and feline bacterial pyelonephritis.
Disruption of local mechanical defense mechanisms
may lead to ascending UTI. For example, vesicoureteral
reflux may result in bacterial cystitis, leading to bacterial
pyelonephritis. During normal micturition, the detrusor
muscle contracts and occludes the ureter so that vesicoureteral reflux cannot occur. This preventive mechanism has been shown to be much weaker in animals
with preexisting UTIs or obstructive urinary disorders.
Congenital ureteral defects (e.g., ectopic ureter) are other
common predisposing causes of bacterial pyelonephritis.
Other local mechanisms against infection are normal uroepithelium and well-concentrated urine. Therefore, epithelial disruption and diseases that lead to
chronically dilute urine may predispose dogs or cats to
UTIs. It has been shown that up to 30% of cats with
chronic renal failure develop bacterial UTIs. Frequent
voiding of urine also helps prevent bacteria from colonizing the lower urinary tract.
Disruption of local immunologic defenses can
allow bacterial colonization of the urinary tract. Diseases that alter the function of the immune system may
lead to decreased neutrophil chemotaxis and a hampered ability to fight off infection. Use of immunosuppressive medications may also decrease immune
function. Either endogenous or exogenous insults to
the normal competency of the immune system may
predispose dogs and cats to bacterial pyelonephritis.
Bacteria implicated in the development of pyelonephritis in dogs and cats are usually normal inhabitants of
the gastrointestinal tract or skin that have managed to colSTANDARDS
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onize the urinary tract. The most common causative
pathogen identified in dogs and cats is Escherichia coli
derived from the normal flora of the gastrointestinal tract.
Certain strains of E. coli appear to have particular virulence
characteristics that allow them to avoid being flushed out
by normal micturition. These bacteria may also survive in
acidic urine and actively ascend up the ureters and into the
kidneys. Other common pathogens reported to cause bacterial pyelonephritis in dogs and cats include Staphylococcus, Streptococcus, and Enterococcus spp. Proteus,
Klebsiella, Pasteurella, Pseudomonas, Corynebacterium,
and Mycoplasma spp are less commonly reported.
Pyelonephritis may be unilateral (ascending UTI) or
bilateral (ascending UTI, hematogenous infection).
Clinical signs of pyelonephritis are varied or may be
absent altogether, making diagnosis a challenge.
DIAGNOSTIC CRITERIA
Historical Information
Gender Predisposition
• Females are more often affected (dogs and cats).
Age Predisposition
• Dogs: None.
• Cats: Older cats with preexisting renal insufficiency
may be more predisposed.
Breed Predisposition
• None recorded.
Owner Observations
• Polyuria and polydipsia.
• Lethargy.
• Vomiting (with acute pyelonephritis).
• Stranguria and/or hematuria.
• Anorexia.
• Weight loss (with chronic pyelonephritis).
Other Historical Considerations/Predispositions
• History of infection:
— Bacterial cystitis, especially if recurrent.
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— Sepsis.
— Bacterial endocarditis.
— Diskospondylitis.
— Septic arthritis.
• Presence of a local condition predisposing to infection:
— Urolithiasis.
— Urinary tract neoplasia.
— Urine retention: Urethral obstruction or neurologic disease (upper motor neuron bladder with
spinal cord lesions above the sacral spinal cord
or lower motor neuron bladder with S1–S3
spinal cord lesions).
— Congenital ureteral defect.
— Juvenile vulvar conformation.
— Chronically dilute urine.
• Presence of a systemic condition predisposing to
infection:
— Diabetes mellitus.
— Hyperadrenocorticism.
— Chronic renal failure.
• Use of immunosuppressive medication.
Physical Examination Findings
• Large, painful kidneys.
• Small, irregular kidneys.
• Fever.
Laboratory Findings
Serum Biochemistry Panel $
• Increased blood urea nitrogen, creatinine, and phosphorus.
Complete Blood Count $
• Increased white blood cell count.
• Immature leukocytosis.
Urinalysis $
• Urine sample collection should be done using a
sterile technique.
• Pyuria, bacteriuria, or proteinuria.
• Inappropriately concentrated urine (often isosthenuric).
• Leukocyte and/or granular casts.
Urine Culture $
• Sampling via cystocentesis or pyelocentesis before
initiation of antibiotic therapy is ideal. In patients
with bleeding tendencies, uncooperative patients
that are not stable enough for sedation, or patients
in which repeated attempts at cystocentesis have
been unsuccessful, it may be prudent to obtain the
sample using a sterile urinary catheter.
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• Documentation of infection.
• Antimicrobial susceptibility testing.
Other Diagnostic Findings
Radiography $
• Bilateral or unilateral renomegaly (acute pyelonephritis).
• Small, irregular kidneys (chronic pyelonephritis).
• Perinephric gas or loss of detail.
• Evidence of nephroliths, ureteroliths, cystic calculi,
or urethral calculi.
• Proximal ureteral dilation or complete dilation if the
patient has a concurrent ectopic ureter.
• Radiography results may be normal.
Ultrasonography $$
• Renal pelvic dilation: Pyelectasis (usually >2 mm).
• Renomegaly (acute pyelonephritis).
• Perirenal gas or fluid.
• Hyperechoic renal cortices (more likely in patients
with chronic pyelonephritis).
• Decreased corticomedullary distinction (more
likely in patients with chronic pyelonephritis).
Contrast-Enhanced Computed Tomography
$$$–$$$$
• Unilateral or bilateral renomegaly (acute pyelonephritis).
• Poor definition of calyceal architecture.
• Blunting of diverticuli.
• Patchy nephrographic appearance on angiography
caused by an atrophied or asymmetric renal cortex.
• Poorly demarcated ischemic areas secondary to
infarction.
• Homogeneous or heterogeneous enhancement of
renal parenchyma.
Excretory Urography (Intravenous Urography
or Pyelography) $$
• Excretory urography helps to rule out ureteral
obstruction as a cause of pyelectasis.
• Dilation of the renal pelvis and/or ureter.
• Blunting of diverticuli.
• Filling defects or fragmentation of contrast within the
collecting system because of accumulation of exudate.
Histopathology $$
• Samples for histopathology may be obtained via
exploratory laparotomy or laparoscopy or using an
ultrasound-guided Tru-Cut biopsy needle.
• Scarring of capsular surface.
• Interstitial mononuclear inflammation.
TA B L E 1
A n t i b i o t i c s f o r I n i t i a l Tr e a t m e n t
Spectrum
and Efficacy
Route of
Elimination
Route of
Administration
Canine
Dosage
Feline
Dosage
Rational
Empiric Use
Ampicillin
Gram +:
Excellent
Gram –: Fair
Anaerobes:
Excellent
Other:
Leptospirosis
Renal filtration
into urine
IV, SC, or IM
22 mg/kg
q8h
22 mg/kg
q8h
Good first choice for
hospitalized patient
with suspected grampositive infection or
suspected
leptospirosis
Amoxicillin
Gram +:
Excellent
Gram –: Fair
Anaerobes:
Excellent
Other:
Leptospirosis
Renal filtration
into urine
PO, IM, or SC
20 mg/kg
q12h
20 mg/kg
q12h
Good first choice for
suspected grampositive infection or
suspected
leptospirosis
Amoxicillin–
clavulanic
acid
Gram +:
Excellent
Gram -: Good
Anaerobes:
Excellent
Renal filtration
into urine
PO
13.75
mg/kg
q12h
62.5 mg
q12h
Good broad
spectrum for possible
mixed infection
while awaiting
culture results
Cefoxitin
Gram +: Good
Gram -: Good
Anaerobes:
Excellent
Renal filtration
into urine
SC, IM, or IV
20 mg/kg
q8h
20 mg/kg
q8h
Good broadspectrum choice for
hospitalized patient
Cefotaxime
Gram +: Fair
Gram -:
Excellent
Anaerobes:
Excellent
Renal filtration
into urine
IV, IM, or SC
30 mg/kg
q8h
30 mg/kg
q8h
Excellent choice for
suspected resistant
infection in
hospitalized patients
Cephalexin
Gram +:
Excellent
Gram -: Good
Anaerobes:
Good
Renal filtration
into urine
Some secretion
into bile
PO
30 mg/kg
q8h
30 mg/kg
q8h
Good first choice
with suspected grampositive infection
Doxycycline
Gram +: Fair
Gram -: Good
Anaerobes: Fair
Other:
Leptospirosis
~75% eliminated
in feces
~20% eliminated
in urine
<5% excreted in
bile
PO or IV
5–10
mg/kg
q12h
5 mg/kg
q12h
Good choice if
underlying
leptospirosis is
suspected
Enrofloxacin
Gram +: Good Renal filtration
Gram -:
into urine
Excellent
Anaerobes: Fair
PO, IM, or IV
10 mg/kg
q24h
5 mg/kg
q24h
Excellent first choice
for suspected gramnegative infection
Ticarcillin–
clavulanic
acid
Gram +:
Excellent
Gram -: Good
Anaerobes:
Excellent
IV or IM
50 mg/kg
q6–8h
50 mg/kg
q6–8h
Excellent broad
spectrum for
suspected resistant
organisms
Drug
Renal filtration
into urine
• Increased interstitial fibrous tissue.
• Leukocyte casts in collecting tubules.
• Pelvis and calyx involvement (infiltration of subenSTANDARDS
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dothelial connective tissue with inflammatory cells).
• Interstitial deposits of Tamm-Horsfall protein precipitates with chronic pyelonephritis.
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Summary of Diagnostic Criteria
• Positive urine culture (ideally from the renal pelvis
but may also be from the lower urinary tract) with
appropriate antimicrobial susceptibility testing.
• Dilated renal pelvis.
• Painful, large kidneys or small, irregular kidneys.
• Immature leukocytosis.
• Azotemia.
• History of polyuria and polydipsia.
• Hyperechoic renal cortices.
Diagnostic Differentials
• Other causes of lower urinary tract signs (hematuria, stranguria): Bacterial cystitis, urolithiasis, sterile cystitis (feline urinary tract disease), urinary tract
neoplasia, hemorrhagic cystitis from cyclophosphamide therapy, disorders of primary hemostasis.
• Other causes of renal failure: Leptospirosis, nephrotoxins, bilateral ureteral obstruction, hypoperfusion,
renal lymphoma, renal dysplasia, chronic interstitial
nephritis.
• Other causes of renomegaly: Hydronephrosis (as
with ureteral obstruction), feline infectious peritonitis, neoplasia.
• Other causes of polyuria and polydipsia: Diabetes
mellitus, hyperadrenocorticism, hypoadrenocorticism, diabetes insipidus, psychogenic water drinking, hypercalcemia, liver disease, hyperthyroidism,
pyometra.
TREATMENT
RECOMMENDATIONS
Initial Treatment
• Antibiotic treatment should be based on culture and
sensitivity. Gram stain may help guide initial antibiotic choices. Reasonable initial choices are listed in
Table 1. $
• Ideally, all antibiotics should initially be given intravenously, especially in cases of acute pyelonephritis.
• Scientific evidence for the appropriate duration of
antibiotic treatment for dogs and cats is lacking.
Current recommendations are to treat initial
episodes for a total of 4 to 6 weeks. Recurrent
episodes may warrant longer treatment times.
Alternative/Optional
Treatments/Therapy
Surgery $$$–$$$$
• Renal or perirenal abscess formation may warrant
surgical intervention.
• Cystic, ureteral, renal, or urethral calculi may need
to be surgically removed if they are serving as a
nidus for recurrent infection, obstructing urine flow,
or causing patient discomfort.
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Lithotripsy $$$–$$$$
• Cystoscopic laser lithotripsy may be used to remove
cystic calculi in patients that are large enough to
accept the instruments (excluding small male dogs
and cats).
• Extracorporeal shock-wave lithotripsy may be used
to fragment uroliths in any site.
Minimally Invasive Procedures $$–$$$$
• Ureteral or urethral stents may be placed with fluoroscopic guidance to facilitate passage of calculi.
• Voiding urohydropulsion may be performed to
remove small cystic and urethral calculi.
• Furosemide, mannitol, amitriptyline, or glucagon
may be used to facilitate passage of ureteral calculi.
• Percutaneous nephrolithotomy may be used when
indicated.
• Cystoscopic laser surgery may be performed for correction of ureteral ectopy.
Supportive Treatment
Fluid Diuresis $
• If renal failure is present, the animal should be hospitalized and given IV fluids until the renal values
have normalized or stabilized.
Pain Medication $
• Tramadol: 2 mg/kg PO bid.
• Buprenorphine: 0.01 mg/kg IV or PO q6–8h.
• Butorphanol: 0.1–0.3 mg/kg IV q6h.
Gastric Antacids $
• Famotidine: 0.5 mg/kg PO or IV sid.
• Ranitidine: 2 mg/kg PO or IV bid.
• Omeprazole: 0.5–1.0 mg/kg PO sid.
• Esomeprazole: 0.5–1.0 mg/kg PO or IV sid.
Phosphate Binders $
• Phosphate binders should be used in patients with
hyperphosphatemia.
• Aluminum hydroxide: 10–30 mg/kg PO with each
meal.
• Aluminum carbonate: 10–30 mg/kg PO with each
meal.
Antihypertensive Agents (If Indicated) $
• Antihypertensive therapy should not be instituted
until the animal is stable and any dehydration has
been resolved with fluid therapy.
• Amlodipine:
— Dogs: 0.1–0.5 mg PO sid or bid.
— Cats: 0.625–2.5 mg PO sid or bid. Cats weighing more than 4 kg may require a higher dosage.
• Enalapril or benazepril:
— Dogs: 0.25–0.5 mg/kg PO sid or bid.
— Cats: 0.25–1 mg/kg PO sid or bid.
Dietary Modifications $
• If renal failure is present, protein- and phosphorusrestricted diets may be useful for long-term management.
• If urolithiasis is present, dietary manipulation may
be indicated depending on the type of stone.
Patient Monitoring
• For patients without a history of UTIs, urine culture
and urinalysis should be performed 3 to 5 days into
therapy (or sooner if desired) and repeated 1 and 4
weeks after cessation of antibiotic therapy.
• For patients with a history of recurrent UTIs, urine
culture should be repeated approximately 1 week
before cessation of antibiotic therapy. A follow-up
urine culture at 8, 12, and 24 weeks after cessation
of therapy is also appropriate.
• For patients with renal failure and any of its sequelae, routine monitoring is indicated as for other
patients in renal failure.
• For patients with urolithiasis being treated medically for dissolution, follow-up radiography should
be conducted, with the interval depending on the
type of stone.
Home Management
• For patients with persistent renal failure, provision
of adequate amounts of water is necessary to help
maintain hydration.
• For cats with persistent renal failure, feeding wet
food provides another source of water.
• Subcutaneous fluid administration may be useful to
provide fluid support to patients in renal failure that
are unable to maintain adequate hydration with
their own intake.
• Dietary and other supportive management of chronic
renal failure should be provided if indicated.
Milestones/Recovery
Time Frames
• The animal should stop straining to urinate after a
few days of appropriate antibiotic therapy.
• Resolution of hematuria should be seen within days
of starting therapy.
• Appetite and general attitude should improve over
the first few days of therapy.
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Treatment Contraindications
• Nephrotoxic drugs.
• Aminoglycosides.
• NSAIDs are usually not recommended because of
concomitant renal insufficiency.
• Placement of urinary catheters should be avoided
because their use may introduce further infection
into the lower urinary tract. If acute renal failure is
present and urine output needs to be measured, use
of a urinary catheter should be strongly considered
because it is imperative to ensure that the animal is
not going into oliguric or anuric renal failure.
PROGNOSIS
Favorable Criteria
• A negative urine culture after cessation of antibiotic
therapy indicates that the infection has cleared.
• Normal renal values on recheck chemistry panels.
• Successful identification and treatment of predisposing factors.
Unfavorable Criteria
•
•
•
•
•
•
•
•
Persistent azotemia.
Positive urine culture despite antibiotic therapy.
Urine casts on subsequent urinalysis.
Urolithiasis may result in recurrent or persistent
infection if uroliths are not removed.
Underlying neoplasia.
Recurrent infections.
Multiple drug-resistant infections.
Oliguria or anuria.
RECOMMENDED READING
Allen TA, Jaenke RS: Pyelonephritis in the dog. Compend Contin
Educ Pract Vet 7(5):421–428, 1985.
Bartges JW: Urinary tract infections, in Ettinger, Feldman EC (eds):
Textbook of Veterinary Internal Medicine. Philadelphia, WB
Saunders, 2005, pp 1800–1808.
O’Brian TR: Radiographic Diagnosis of Abdominal Disorders in the
Dog and Cat: Radiographic Interpretation, Clinical Signs and
Pathophysiology. Philadelphia, WB Saunders, 1978, pp 520–521.
Osborne CA, Lees GE: Bacterial infections of the canine and feline
urinary tract, in Osborne CA, Delmar FR (eds): Canine and
Feline Nephrology and Urology. Philadelphia, Lea & Febiger,
1995, pp 759–797.
Senior DF: Management of urinary tract infections, in Elliott J,
Grauer GF (eds): BSAVA Manual of Canine and Feline Nephrology and Urology. Gloucester, BSAVA, 2007, pp 282–290.
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