Pyelonephritis is an inflammatory response of the kidney due to bacterial infections and frequently results in acute or chronic renal disease.
If the conditions continues, pyonephrosis may occur, characterized by elevated pressure (similar to hydronephrosis) and suppurative destruction of the parenchyma of the kidney with complete or nearly complete loss of renal function.
The majority of cases are infections limited to the renal pelvis and caused by ascending infections from the bladder due to cystitis.
Secondary causes of pyelonephritis include congenital diseases such as:
- vestibulovaginal stenosis, pelvic bladder, recessed vulva
- renal dysplasia and polycystic kidney disease, urolithiasis (which acts as a nidus for bacterial spread)
- post-operative complications from ectopic ureter correction
- bladder torsion
- urinary tract neoplasia
- use of immunosuppressive drugs such as prednisolone or cyclosporine
- Fanconi's syndrome
- renal toxins
- hematogenous spread of bacteria from other organs - e.g. septicemia, septic endocarditis, osteomyelitis, discospondylitis
Infectious agents implicated in the development of pyelonephritis include:
- - Escherichia coli
- - Staphylococcus hyicus
- - Streptococcus β-haemolyticus
- - Enterococcus spp
- - Proteus spp
- - Klebsiella spp
- - Leptospira spp
- - Pasteurella spp
- - Pseudomonas spp
- - Corynebacterium spp
- - Salmonella spp
- - Mycoplasma spp
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.
Anorexia, fever, renal pain and haematuria may be ascertained from clinical and laboratory examination but some dogs are asymptomatic and only diagnosed after chronic renal disease has established, with signs of uremia, hyperkalemia and polyuria/polydipsia.
Ultrasound imaging may reveal renomegaly and renal pelvic dilatation.
Polycythemia has been reported as a rare side-effect associated with necrotizing pyelonephritis in the dog, presumably due to increased erythropoietin levels.
Urine culture may return a positive bacterial growth but whether this is renal or urinary bladder origin is debatable.
Treatment is based on culture and sensitivity testing of urine and response to therapy. Cephalosporins or amoxycillin/clavulanate are first drugs of choice.
in cases of severe infections with secondary pyonephrosis, percutaneous ultrasound-guided drainage of the renal pelvis and flushing with povidone iodine solutionmay be required.
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