Clinical diagnosis of pyelonephritis often presumptive

April 1, 2002
Johnny D. Hoskins, DVM, PhD, DACVIM

Dr. Johnny Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine and he is a member of DVM Newsmagazine's Editorial Advisory Board.

The dog presents for weight loss, acting strangely and urinary incontinence.

Signalment:

Canine, Papillon, 14-year-old, male castrated, 3.12 lbs.

Clinical history:

The dog presents for weight loss, acting strangely and urinary incontinence. Details of the past medical history indicate two years ago a cystotomy was performed for uroliths. At that time, the CBC was normal and serum chemistry profile showed an increase in BUN (54 mg/dl) and ALT (78 U/L) and a decrease in albumin (1.1 g/dl).

Table 1

Note: There was no ascites present at the time; therefore, the serum albumin value must have been incorrect. The urinalysis showed specific gravity 1.020 and 100+ protein. The urolith analysis showed the mineral content to calcium oxalate.

Seven months later another blood evaluation was done, and it showed the CBC to be normal and serum chemistry profile showed an increase in BUN (44 mg/dl) and amylase (1,260 U/L). The serum albumin value was 3.2 g/dl.

Physical examination:

The findings include rectal temperature 101.9° F, heart rate 135/min, respiratory rate 20/min, pink mucous membranes, normal capillary refill time, and normal heart and lung sounds. Abnormal physical findings are severe dental disease, slight enlarged kidneys on palpation, painful coxofemoral joint or dorsal spine and a lot of urine sediment material attached to the hair at the tip of the prepuce.

Laboratory results:

A complete blood count, serum chemistry profile and urinalysis were performed and are in Table 1.

Radiographic review

Survey thoracic and abdominal radiographs were done. The thoracic radiographs are normal. The abdominal radiographs show an overdistended urinary bladder and multiple urethral calculi located behind the os penis.

Photo 1

Follow-up:

At this point, the urethral calculi needed to be dislodged and good urine flow re-established. I suspect these urethral calculi are of the calcium oxalate type, as before. I cannot rule out the possibility that other calcium oxalate calculi are present in the urinary bladder, ureters and kidneys. Ultrasonography of the upper and lower urinary tract would be recommended.

Immediately, an appropriate sized urinary catheter was passed along with simultaneous hydropropulsion of the urethral calculi toward the urinary bladder (of course, some words of frustration while performing this procedure). Thirteen days after dislodgement of the urethral calculi, the BUN was 79 mg/dl, serum creatinine was 1.1 mg/dl, serum phosphorus was 4.3, and serum albumin was 1.9 g/dl. At this time, a urinary catheter is placed in the distal urethra and contrast material is infused into the lumen of the urethra via the urinary catheter until the urinary bladder is palpated as being distended.

My comments:

The contrast material flowed easily up the urethra into the lumen of the urinary bladder and then the contrast flow was noted in the left ureter and on into the pelvis of the left kidney. The left ureter and renal pelvis are slightly dilated, and the renal pelvis shows blunting of the diverticula. No contrast material was noted in the right ureter and kidney.

Case management

In this case, chronic renal disease is present. Because of the ongoing weight loss, the decreased serum albumin should be investigated. Is there significant proteinuria present?

In this case, I would do a urine protein-to-creatinine ratio. Urine protein-to-creatinine ratio of 3 or greater may be treated with daily administration of lisinopril at 0.25-0.5 mg/kg orally once daily.

Photo 2

To manage the existing cystic calculi, abdominal surgery was subsequently performed. At surgery, a splenic mass was identified, left kidney was slightly enlarged along with the left ureter, and multiple small cystic calculi were found. The spleen was removed and biopsies were obtained from the polar regions of the left kidney. The histopathologic report for the spleen indicated a grade 3 hemangiosarcoma and renal biopsies showed evidence of severe chronic interstitial nephritis.

Canine pyelonephritis

Natural host defenses against ascending urinary tract infection include mucosal defense barriers, ureteral peristalsis, ureterovesical flap valves and an extensive renal blood supply. Pyelonephritis usually occurs by ascension of bacteria causing lower urinary tract infection. Hematogenous seeding of the kidneys does not usually cause pyelonephritis.

In addition, an upper urinary tract infection is frequently accompanied by lower urinary tract infection.

Ascending urinary tract infections probably occurs much more commonly than is recognized clinically - because many older dogs with pyelonephritis are asymptomatic or have signs limited to lower urinary tract infection.

Signs of pyelonephritis may be none or include polyuria/polydipsia, abdominal or lumbar pain, and/or signs associated with lower urinary tract infection - dysuria, pollakiuria, stranguria, hematuria and malodorous or discolored urine. The physical examination may show no abnormalities or pain on palpation of kidneys and a fever.

The ascending urinary tract infection may be caused by aerobic bacteria - most common bacterial isolates are Escherichia coli and Staphylococcus species and less common bacterial isolates may include Proteus, Streptococcus, Klebsiella, Enterobacter and Pseudomonas species, which frequently infect the lower urinary tract and may ascend into the upper urinary tract. Ectopic ureters, vesicoureteral reflux, congenital renal dysplasia and lower urinary tract infection increases the risk of an ascending urinary tract infection. Medical conditions that often predispose the dog to a urinary tract infection are diabetes mellitus, hyperadrenocorticism, exogenous steroid administration, renal failure, urethral catheterization, urine retention, uroliths and urinary tract neoplasia.

Making the diagnosis

Clinical diagnosis of pyelonephritis is often presumptive - based on results from CBC, serum chemistry profile, urinalysis, urine culture and imaging procedures.

Photo 3

A definitive diagnosis is not usually required for planning treatment. Because many dogs lack specific signs attributable to pyelonephritis, any dog with urinary tract infection could potentially have pyelonephritis.

Always consider the possibility of pyelonephritis as a differential diagnosis for any dog with fever of unknown origin, polydipsia/polyuria, chronic renal failure and/or lumbar/abdominal pain. The CBC results are often normal with chronic pyelonephritis, but leukocytosis and neutrophilia with a left shift may be detected in some dogs. The serum chemistry profile is usually normal unless chronic pyelonephritis is contributing to chronic renal failure (azotemia with an inappropriate urinary specific gravity). The urinalysis may reveal hematuria, pyuria, proteinuria, bacteriuria and leukocyte casts. Leukocyte casts are diagnostic for renal inflammation and usually result from pyelonephritis.

Remember that dilute urine specific gravity in dogs with nephrogenic diabetes insipidus may occur secondary to pyelonephritis and absence of abnormalities does not rule out pyelonephritis.

Dogs with chronic pyelonephritis may have a negative urine culture and require multiple urine cultures to confirm urinary tract infection. The new IndicatoRx device (IDEXX) is excellent for obtaining immediate bacterial urine culture results – results are obtained overnight and done in-hospital. Small numbers of bacteria may be recovered with this system.

Ultrasonography and excretory urography are the preferred imaging procedures done for presumptively differentiating between upper and lower urinary tract infection.

Ultrasonographic findings supporting pyelonephritis include dilation of the renal pelvis and proximal ureter and a hyperechoic mucosal margin line within the renal pelvis and/or proximal ureter. Excretory urography may show dilation and blunting of the renal pelvis with lack of filling of the collecting diverticula, and dilation of the proximal ureter. In dogs with acute pyelonephritis, the kidneys may be large; in dogs with chronic pyelonephritis, the kidneys may be small with an irregular surface contour. Concomitant nephroliths may be seen in some dogs evaluated by survey radiography, ultrasonography or excretory urography.

Definitive diagnosis requires urine cultures obtained from the renal pelvis or parenchyma or histopathology from a renal biopsy. Pyelocentesis can be performed percutaneously using ultrasound guidance or during exploratory surgery and immediately transferred to the IndicatoRx device. To confirm the diagnosis the biopsy specimen should include the renal cortex and medulla. Recurrent pyelonephritis may be asymptomatic. Unresolved chronic pyelonephritis may lead to chronic renal failure, and diagnostic follow-up, therefore, is important to document resolution of the pyelonephritis. In dogs with nephroliths, resolution is unlikely unless the nephroliths are removed.

One should preferentially base the antibiotic selection on urine culture and sensitivity testing. Antibiotics used should achieve good serum and urine concentrations and not be nephrotoxic.

High serum and urinary antibiotic concentrations do not necessarily ensure high tissue concentrations in the renal medulla; therefore, chronic pyelonephritis may be difficult to cure.

Do give orally administered antibiotics at full therapeutic dosages for at least six weeks. Do not use aminoglycosides unless no other alternatives exist on the basis of urine culture and sensitivity testing. The trimethoprim/sulfa combinations can cause significant side effects (keratoconjunctivitis sicca, blood dyscrasias, polyarthritis) when administered for more than four weeks. Do urine cultures and urinalysis during antibiotic administration (approximately one-week into treatment) and one and four weeks after antibiotics are finished.

Dogs with pyelonephritis will usually return to normal health unless the dog also has nephrolithiasis, chronic renal failure or some other underlying cause for urinary tract infection. Established infection of the renal medulla may be difficult to resolve because of poor tissue penetration of antibiotics.