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Pyelonephritis in the dog

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Category: Schede
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  • Disciplina: Cardiologia
  • Specie: Cane

Pyelonephritis is defined as an inflammatory process of the renal parenchyma and pelvis: the structures that can be involved are, therefore the renal papilla, cortex and medulla. Inflammation of only the pelvis is called pyelitis and, in the dog, is more common than pyelonephritis.1,2

Pyelonephritis may be unilateral or bilateral: in the former case the animal is usually asymptomatic and the condition is often an incidental post-mortem finding, whereas if the process affects both kidneys it can progress, causing chronic renal failure.

 

AETIOPATHOGENESIS

In acute cases the inflammation may involve only the renal papilla and pelvis and then extend, in chronic cases, to the medulla and cortex. The inflammatory process is tubulo-interstitial and characterized by infiltration of neutrophils and necrosis: it can lead to varying degrees of renal fibrosis and, finally, to atrophic sequelae.

Most cases of pyelonephritis are caused by bacteria,3,4,5 although infections by fungi,6,7,8viruses4 and parasites may also be responsible. The bacteria most frequently implicated are Gram-negative organisms and, from among these, Escherichia coli is the major cause of pyelonephritis in the dog.3,4,5 The infection usually reaches the kidney through an ascending pathway: the route of infection is, therefore, backflow of bacteria from any point along the lower urinary tract.

Although this is the most typical form of pyelonephritis, the renal parenchyma can become infected by embolic-metastatic infective foci: the underlying feature in this process is the presence of bacteraemia or septicaemia (secondary to gastrointestinal tract infections, endocarditis, discospondylitis or pyometra).

 

PREDISPOSING FACTORS

The factors predisposing to the development of pyelonephritis can be divided into essentially three groups: anatomic anomalies, functional and/or metabolic abnormalities and the presence of infections.

  1. Anatomic anomalies: all those alterations that cause urinary reflux or stasis can act as factors predisposing to the onset of pyelonephritis (ectopic ureters, abnormalities of the bladder or urethra, stenosis,9neoplasms10).
  2. Functional and/or metabolic abnormalities: vesico-ureteral or pyelo-tubular reflux, glycosuria, papillary ischaemia or a state of immunosuppression9 also act as predisposing factors.
  3. Infections: infections of the lower urinary tract, prostate and permanent indwelling catheters predispose to the development of pyelonephritis.11

 

CLINICAL SIGNS

The clinical signs of acute pyelonephritis are very varied: some animals appear completely asymptomatic, while others show signs of septicaemia. Acute pyelonephritis may cause fever, anorexia, lethargy, vomiting and renal and lumbar pain.3,12

Animals with chronic pyelonephritis may have polyuria and polydipsia because inflammation of the renal interstitium prevents the maintenance of medullary osmolarity, thus limiting the capacity to concentrate the urine. Although most patients do not show signs of lower urinary tract infection (frequency, strangury, haematuria, urgency), these may be present.

 

DIAGNOSIS

Numerous investigations must be conducted before being able to confirm or exclude a suspected diagnosis of pyelonephritis.

An examination of urinary sediment often reveals bacteria and/or granulocytes in the urine, indicating the presence of an infection of the urinary tract (Fig. 1): this is, however, only a weakly specific finding. The sediment may contain casts with granulocyte inclusions and upper urinary tract cells (Fig. 2): these findings constitute more specific support for a diagnosis of pyelonephritis.13

The specific gravity of the urine is usually decreased, but there may also be isosthenuria during chronic disease and, in this case, the process is irreversible.14,15

Blood tests may reveal leucocytosis, which is not usually present in patients with lower urinary tract infection.3 In the cases in which both kidneys are affected, the blood-chemistry examinations may show uraemia, electrolyte disturbances and disordered acid-base balance.

Urine culture is always indicated, using urine taken by cystocentesis, even when there are no detectable changes in the urinary sediment; unfortunately, even a positive urine culture by itself has limited diagnostic significance because, just as for the examination of sediment, it dos not enable the site of the infection to be determined. For this reason, in some cases the diagnosis of pyelonephritis may be made by culturing a sample of urine taken directly from the renal pelvis by percutaneous nephropyelocentesis.

Furthermore, it should be remembered that negative microbiological studies do not exclude the presence of pyelonephritis and that, when all other causes of polyuria and polydipsia have been investigated and excluded, empirical antibiotic treatment is indicated: in this case, an improvement in the clinical signs confirms the diagnosis.

Plain X-rays are of little help, but intravenous pyelography may be useful. The radiographic changes include dilatation of the renal pelvis and the proximal part of the ureter and decreased opacity of the contrast agent in the collecting system and vascular nephrogram;13,16 the kidney may be enlarged in the acute stage of the disorder and then become smaller as the disease progresses.13

Ultrasonography is also useful for diagnostic purposes:17 the ultrasound signs that are compatible with a diagnosis of pyelonephritis are dilatation of the renal pelvis, a hyperechoic band of pelvic mucosa, hypoechoic areas in the medulla, focal cortical lesions that may be either hyperechoic or hypoechoic, and increased echogenicity of the ureter (Figs. 3 and 4).

Unfortunately, both radiographic studies with contrast agents and ultrasonography may be normal in some patients with pyelonephritis.17 In humans, computed tomography with dimercaptosuccinic acid can be used,18,19 but no studies have been performed with this technique in dogs or cats.

A renal biopsy is unlikely to provide useful information because of the small amount of kidney which is sampled and examined; however, is some cases it may be possible to identify small areas of tubulo-interstitial nephritis by microscopy: in acute cases a large number of neutrophils are present, whereas in chronic pyelonephritis there may be interstitial fibrosis.

 

TREATMENT

In order to establish the correct therapeutic protocol, it is essential to determine whether there are any predisposing factors present which must be corrected: pyelonephritis can, in fact, be difficult to treat.

The antibiotic must be selected on the basis of the results of microbiological studies and an antibiogram; treatment should be prolonged and is often continued for more than 4 weeks: it is important to carry out urine cultures periodically during the treatment and monthly after the therapy has been suspended in order to monitor the efficacy of the antibiotic and detect any recurrences promptly. Obviously, in the presence of chronic kidney disease, appropriate therapy must be administered concomitantly.

Possible therapeutic options include nephrectomy20 which should only be used in animals with unilateral disease and a normally functioning contralateral kidney. The possibility of ultrasound-guided percutaneous drainage for therapeutic purposes has also been reported.21

Unfortunately, in some subjects the infection cannot be resolved and the treatment must be aimed at controlling the clinical symptoms.

 

References

  1. Christie BA: “The occurrence of vescicoureteral reflux and pyelonephritis in apparently normal dogs.” Invest Urol. 1973 Mar;10(5):359-66.
  2. CrowellWA, Finco DR: “Frequency of pyelitis, pyelonephritis, renal perivasculitis and renal infarction in dogs.” Am J Vet Res. 1975 Jan;36(1):111-4.
  3. Finco DR, Barsanti JA: “Bacterial pyelonephritis” Vet Clin North Am Small Anim Pract. 1980 Nov;9(4):645-60.
  4. Ginder DR: “Urinary tract infection and pyelonephritis due to Escherichia Coli in dogs infected with canine adenovirus.” J Infect Dis. 1974 Jun;129(6):715-9.
  5. Yuri K, Nakata K, Hatae H, Hasegawa A: “Pathogenicity of Escehrichia Coli from dogs with UTI in relation to urovirulence factors.”J Vet Med Sci. 2000 Nov;62(11):1197-200.
  6. Bray JP, White RA, Lascelles BD: “Treatment of canine nasal aspergillosis with a new non-invasive technique. Failure with enilconazole.” J Small Anim Pract. 1998 May;39(5):223-6.
  7. Day MJ, Holt PE: “Unilateral fungal pyelonephritis in a dog.” Vet Pathol. 1994 Mar;31(2):250-2.
  8. Newman SJ, Langston CE, Scase TJ: “Cryptococcal pyelonephritis in a dog.” J Am Vet Med Assoc. 2003 Jan 15;222(2):180-3, 174.
  9. CrowellWA, Finco DR, Rawilings CA, Barsanti JA, Rao RN: “Lesions in dogs following renal transplantation and immunosuppression” Vet Pathol. 1987 Mar;24(2):124-8.
  10. Jergens AE, Miles KG, Turk M: “Bilateral pyelonephritis and hydroureter associated with metastatic adenocarcinoma in a dog.” J Am Vet Med Assoc. 1988 Oct 15;193(8):961-3.
  11. Barsanti JA, Shotts EB, Crowell WA, Finco DR, Brown J: “Effect of therapy on susceptibility to urinary tract infection in male cats with indwelling urethral catheters.” J Vet Intern Med. 1992 Mar-Apr;6(2):64-70.
  12. Finco DR, Shotts EB Jr, Crowell WA: “Evaluation of methods for localization of urinary tract infection in the female dog.”Am J Vet Res. 1979 May;40(5):707-12.
  13. Barber DL, Finco DR: “Radiographic findings in induced bacterial pyelonephritis in dogs.” J Am Vet Med Assoc. 1979 Dec 1;175(11):1183-90.
  14. Levison SP, Levison ME: “Effect of indomethacin and sodium meclofenamate on the renal concentration detect in experimental enterococcal pyelonephritis in rats.”J Lab Clin Med. 1976 Dec;88(6):958-64.
  15. Ronald AR, Cutler RE, Turck M: “Effect of bacteriuria on renal concentrating mechanism” Ann Intern Med. 1969 Apr;70(4):723-33.
  16. KnellerSK: “Role of the excretory urogram in the diagnosis of renal and ureteral disease.” Vet Clin North Am. 1974 Nov;4(4):843-61.
  17. Neuwith L, Mahaffey M, Crowell W, Selcer B, Barsanti J, Cooper R, Brown J: “Comparison of excretory urography and ultrasonography for detection of experimentally induced pyelonephritis in dogs.”Am J Vet Res. 1993 May;54(5):660-9.
  18. Goldraich NP, Ramos OL, Goldraich IH: “Urography versus DMSA scan in children with vesicoureteric reflux.” Pediatr Nephrol. 1989 Jan;3(1):1-5.
  19. Smellie JM, Shaw PJ, Prescod NP, Bantock HM: “99mTc dimercaptosuccinic acid (DMSA) scan in patients with established radiological renal scarring.” Arch Dis Child. 1988 Nov;63(11):1315-9.
  20. Gookin JL, Stone EA, Spaulding KA, Berry CR: “Unilateral nephrectomy in dogs with renal disease: 30 cases (1985-1994).” J Am Vet Med Assoc. 1996 Jun 15;208(12):2020-6.
  21. Szatmàri V, Osi Z, Manczur F: “Ultrasound-guided percutaneous drainage for treatment of pyonephrosis in two dogs.” J Am Vet Med Assoc. 2001 Jun 1;218(11):1796-9, 1778-9.

 

Suggested readings

  1. BSAVA Manual of Canine and Feline Nephrology and Urology Second edition, Edited by Johnathan Elliot and Gregory F. Grauer, 2007.
  2. Osborne CA, Finco DR: Canine and feline nephrology and urology. Williams & Wilkins, Philadelphia, 1995