Animal Care Clinic
Nephrology & Urology
Pyelonephritis is an inflammation of the kidney that is preferential to the renal medulla (with radiating involvement to the renal cortex) and is most often due to a bacterial infection that has ascended from the lower urinary tract to the kidney. The clinical signs associated with pyelonephritis may be mild, or even unnoticed; however, pyelonephritis can lead to kidney failure, sepsis and even death, if not addressed. Depending on the specific case, certain diagnostics and therapeutics are recommended and tailored to each individual. Pyelonephritis can be either acute or chronic. Pyelonephritis is often an elusive diagnosis that is hard to establish since positive "classic" indicators for this disease are often not found at the time of evaluation.
DIAGNOSIS OF PYELONEPHRITIS
ETIOLOGY AND RISK FACTORS
- Causes - Pyelonephritis may be caused by ascending urinary tract infections; hematogenous or lymphogenous seeding of infection is much less common. The most common bacterial causes of pyelonephritis include Escherichia coli, Pseudomonas, Staphylococcus, Klebsiella, Streptococcus, Enterobacter and Proteus.
- Risk factors
- Age - No known risk
- Breed/genetics - No known risk
- Sex - In dogs, urinary tract infections in general are more common in females than males
- Geographic/environmental - No known risk
- Other medical disorders - There may be factors that enhance the susceptibility to infection such as congenital abnormalities, metabolic disorders or systemic immunosuppression; however, no recognizable underlying disorders need exist, though often there is an element of urinary obstruction at some level that allows upper urinary infection to exist.
- Prevention - Prompt treatment of lower urinary tract infections may lessen the likelihood of developing pyelonephritis.
HISTORY AND CLINICAL SIGNS
- Species affected - Dogs are more commonly diagnosed than cats, though the presence of pyelonephritis in cats may equal or exceed that in dogs. The lesions of "idiopathic" CRF in cats resemble that which is created following experimental pyelonephritis. Cats with spontaneous CRF often develop bacterial UTI. Some of these may be involved with upper urinary tract infection either as a primary or secondary condition.
- Presenting signs and historical problems - Common signs associated with pyelonephritis include polyuria/polydipsia, abdominal or back pain and signs associated with lower urinary tract infection including dysuria, pollakiuria, stranguria, hematuria and malodorous urinations. Additionally, systemic signs of illness, including fever, vomiting, diarrhea, lethargy and inappetence, may be apparent as well. Animals with acute pyelonephritis usually have more obvious and severe clinical signs than do those animals with chronic pyelonephritis. Clinical signs during acute pyelonephritis may be quite transient. Animals with chronic pyelonephritis may exhibit no clinical signs depending on the degree of renal damage created by the infection.
PHYSICAL EXAMINATION FINDINGS
- Attitude - Mental status may vary from lethargy to severe depression.
- Body condition - Chronic pyelonephritis may result in weight loss and a poor body condition.
- Vital signs - Respiratory rate and pulse are often normal. A fever may be detected early in the disease in acute cases; fever is often absent in chronic cases.
- Mucous membranes - Gum color is often normal but capillary refill time may be delayed due to dehydration.
- Hydration status - Patients may be dehydrated especially during acute pyelonephritis.
- Abdominal pain may be present that is difficult to localize to the kidney(s). The kidneys may be enlarged or painful during acute pyelonephritis; shrunken and irregular kidneys may be discovered in those with chronic pyelonephritis.
- The remainder of the physical exam is unremarkable
- Clinical laboratory tests
- CBC - A complete blood count is usually within normal limits during chronic pyelonephritis; however, an elevated white blood cell count with a left shift may be observed in some with acute pyelonephritis though this is often transient.
- Serum biochemical tests - A biochemical profile may be within normal limits; however, it may reveal increased BUN/creatinine and elevated phosphorus due to combinations of primary renal lesions and pre-renal factors.
- Urinalysis - A urinalysis may reveal hematuria, pyuria, proteinuria, bacteriuria or white blood cell casts. The finding of minimally concentrated or dilute urine in those with a positive urine culture can be supportive for diagnosis of pyelonephritis. The absence of any or all of these does not rule out pyelonephritis especially if the case is chronic.
- Microbiology - A bacterial urine culture is performed to confirm a urinary tract infection; however, it may be negative in some cases of pyelonephritis. A bacterial culture of the renal pelvis may be obtained with the guidance of abdominal ultrasound if the bladder urine culture is negative. It is generally assumed that organisms isolated from cystocentesis are also in the kidneys if there are other compatible findings on physical examination, urinalysis and renal imaging. Nephropyelocentesis is NOT a routine procedure and should be done by a specialist. It is important to remember that a positive quantitative urine culture documents UTI but not whether it is upper, lower or both.
- Diagnostic imaging
- Radiographs (abdominal) - Abdominal radiographs may be within normal limits, they may reveal changes in kidney size, urinary calculi, or they may rule out other diseases and causes of clinical signs
- Contrast radiography - Excretory urography is helpful in documenting pyelonephritis and is also of benefit in some cases to detect stones in the urinary tract and may identify other abnormalities, such as ectopic ureters. Dilatation of the proximal ureter as a sign supportive of pyelonephritis is far more readily observed during IVP than during ultrasound.
- Ultrasound (abdominal) - Abdominal ultrasound is recommended in most suspected cases. It is helpful in evaluating the kidney and differentiating between upper and lower urinary tract infection. Characteristic changes are seen within the renal pelvis that is consistent with pyelonephritis (pyelectasia, dilatation of diverticula). Kidneys may be enlarged in acute cases, and small in chronic cases. Ultrasound is also helpful in evaluating for the presence of stones throughout the urinary tract but is limited for evaluation of the ureter and the urethra.
- Biopsy/histopathology - In selected cases, a kidney biopsy may be of benefit in diagnosing pyelonephritis. This is an invasive procedure that may be performed with the guidance of ultrasound; however, exploratory surgery may be necessary in certain cases since the lesions predominate in the medulla and a deeper wedge of tissue may be needed to make the diagnosis. Fine needle aspirate may reveal findings of neutrophils and bacteria that are supportive in cases with acute pyelonephritis.
DIAGNOSIS AND PROGNOSIS
- Differential diagnosis - Several diseases/disorders can present similarly to pyelonephritis. These include:
- Urolithiasis anywhere throughout the urinary tract may be associated with and present similarly to patients with pyelonephritis
- Lower urinary tract infection needs to be differentiated from pyelonephritis. This is not easy to do, as there are no gold-standard tests that make this distinction.
- Chronic renal failure may be associated with, the result of, or simply present without pyelonephritis.
- Bacterial prostatitis and metritis can present similarly to animals with pyelonephritis. It is not uncommon for these individuals to have a fever and elevations in their white blood counts and experience abdominal pain
- Other causes of fever and painful abdomen such as pancreatitis or peritonitis need to be considered, as some animals with pyelonephritis present for abdominal pain.
- Other causes of polyuria/polydipsia to include hyperadrenocorticism, diabetes mellitus, kidney disease and liver disease needs to be ruled out.
- Recommended tests - CBC, biochemical profile, urinalysis, urine culture and abdominal ultrasound.
- Summary of diagnostic criteria - CBC, biochemical profile and urinalysis results as described above. Abdominal ultrasound or IVP may reveal characteristic findings as described above
- Prognosis - With appropriate therapy, patients with acute pyelonephritis can do well if underlying predispositions can be corrected (stones, strictures, urinary emptying disorders). Prognosis for acute pyelonephritis should be guarded - some will develop chronic pyelonephritis and some will develop CRF. In chronic pyelonephritis, the response to therapy can take longer, and occasionally, response may be poor. Prognosis in chronic pyelonephritis should be guarded to poor until the patient response can be evaluated. In some cases it is impossible to sterilize the renal tissue despite the use of appropriate antimicrobial therapy. Reinfection or relapsing infection occurs commonly in cats with CRF and UTI.
TREATMENT OF PYELONEPHRITIS
Stable patients, some cases with acute and most with chronic pyelonephritis, can be treated as outpatients as long as they are monitored closely for response to therapy
- Correction of any underlying predisposing factors such as ectopic ureters, urolithiasis, or prostatitis is imperative to treatment
- Antibiotic therapy selected on the basis of bacterial culture and sensitivity of the urine or renal tissue is the most important part of therapy. Usually, a minimum of a 4- to 6-week treatment protocol is indicated. If necessary, antibiotic therapy can be instituted prior to culture results. A common antibiotic choice is a combination of ampicillin and enrofloxacin. Caution should be used in the use of enrofloxacin in cats with renal failure due to the possibility of sudden and irreversible blindness. Its use is recommended only if other drugs are not effective.
- Dietary modification is recommended for animals with concurrent kidney failure or urolithiasis.
- Hospitalization, intravenous fluid therapy and antibiotic administration may be necessary in some cases of acute pyelonephritis, especially if sepsis is suspected (acute or chronic).
- Surgical intervention may be necessary in cases of pyelonephritis associated with or secondary to urinary calculi.
LONG - TERM/HOME THERAPY
Continued antibiotic therapy is crucial. Many dogs require 4 to 6 weeks of treatment or longer.
Repeat the urine culture and urinalysis approximately 7 to 10 days into treatment as a method of in vivo susceptibility testing. The urine should be sterile. Reculture at 1 to 2 weeks after the entire course of treatment has been completed to ensure that a relapse is not happening (even in the absence of clinical signs). It is important to obtain urine cultures every 2 to 3 months until 3 negative cultures are obtained. If at any point the culture is positive, an additional course of antibiotics, often longer than the original course, is generally recommended. Infection may persist in some animals despite appropriate, repeated courses of antibiotics.
General blood work, complete blood count and biochemical profile, may need to be reevaluated as needed.
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|7:30AM – 7:00PM|
|7:30AM – 7:00PM|
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|7:30AM – 7:00PM|
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