Case Study: Bladder Stones

History

Shiloh, a 3-year-old long-haired intact female Chihuahua, presented for frequent urination and hematuria of several days duration. She had been acting normally otherwise and had no prior history of any serious health concerns.

Presentation

Shiloh was quiet and a little shy, but overall was alert and responsive. She urinated on the floor during the exam and the urine was grossly hematuric. Her physical exam was normal except for mild dental calculus, and on abdominal palpation a hard, smooth object was noted in the caudal abdomen.

Differential diagnoses included cystitis, urolithiasis, and neoplasia. Pyometra or metritis were not considered likely possibilities due to the density of the object and its well-delineated borders.

Diagnostic Tests

Urinalysis: Positive for bacteria (cocci), leukocytes and erythrocytes. pH 6.0. No crystalluria noted.

Abdominal radiographs: large, oval mineral radiopacity object in caudal abdomen, consistent with a urolith (Figure 1).

Figure 1- Radiograph of patient showing radiopaque oval object in the caudal abdomen, in the region of the urinary bladder.

Discussion points to consider

1. What is your next step and why?
2. Based on the history and the lab findings, what type of bladder stones would you include in your differential list?
3. How likely is it that this case would improve with only medical therapy? What would that therapy be?
4. What is the likelihood of chronic or recurrent problems in this patient?

Treatment

Surgical removal of the urolith was recommended, but the client could not afford such treatment at the time. Shiloh was prescribed amoxicillin-clavulanic acid 62.5 mg BID PO for two weeks. Her owner was given instructions to observe her closely and present her for a recheck when the course of antibiotics was finished. Shiloh was also prescribed Royal Canin Urinary S/O diet.

Second Presentation

Three weeks later, Shiloh re-presented for lethargy, difficulty defecating and urinating, and discomfort. A physical exam revealed no new findings from the previous visit. Shiloh was hospitalized for the day and showed signs of dysuria, although she was not anuric. Further diagnostic testing was performed.

Diagnostic Tests

Chemistry Profile: WNL
CBC: Increased leukocytes (25,190/µL), otherwise WNL

Discussion Points to Consider

1. Does your plan or recommendation change on this second visit?
2. How do you communicate your recommendations to the client at this point?
3. What are the potential consequences of not performing surgery at this time?
4. If the symptoms continue to persist or worsen and the owner cannot afford surgery, what is your recommendation?

Treatment

Based on Shiloh’s symptoms and the results of the lab tests, it was suspected that the large bladder stone was causing pain and discomfort. Shiloh was prescribed 12.5 mg carprofen (1/2 25 mg tablet) PO q24h while the owner decided on further care.

Shiloh’s owner was able to secure finances and authorized surgery. Preanesthetic medications were acepromazine 0.2mg IM and 1.6 mg butorphanol IM. A 22 ga catheter was placed and anesthesia induced with propofol, then maintained with sevoflurane via endotracheal tube. The ventral abdomen was shaved and scrubbed for surgery. An incision was made along the ventral midline in the caudal abdomen, the bladder identified and exteriorized, and stay sutures placed (3-0 PDS). Laparotomy sponges were placed around the bladder to prevent urine leakage into the abdomen. The dorsal body of the urinary bladder was incised and urine evacuated, allowing exposure and exploration of the contents. A single oval urolith was identified and removed (Figures 2, 3). Further exploration and repeated radiographs revealed no additional uroliths. The bladder wall was considerably inflamed and thickened, but no signs of necrosis or other damage were visible. The bladder was closed with a double layer of 3-0 PDS with a simple interrupted pattern. After bladder closure, a leak test was performed with 10cc of sterile saline and no leaks were detected. The abdomen was closed normally with 3-0 PDS; the linea alba, subcutaneous and intradermal tissues were closed using a simple continuous pattern and Vetbond was used for skin closure. Patient recovery was uneventful. Shiloh was sent home with tramadol 25 mg PO BID-TID PRN for pain and amoxicillin-clavulanic acid 62.5mg PO BID for seven days. The post-operative period and recovery were normal.

Figure 2- Intraoperative image showing the urolith as it is being removed from the bladder.

Figure 3- Urolith postoperative with a scalpel handle as a sizing guide.

A piece of the urolith was sent for analysis, which showed it was 40 percent struvite and 60 percent ammonium urate both externally and internally with no nidus.

Overview

Struvite is the most common type of urolith in dogs. Most struvite uroliths form in alkaline urine as a result of urinary tract infections caused by urease-producing organisms. Medical dissolution may be successful in some cases, especially if the uroliths are small. If the urolith is large or the composition is unknown (such as in this case), surgical removal is necessary. Long-term management of struvite uroliths is normally achieved through appropriate use of dietary therapy to encourage dilution of urine and a slightly acidic pH.

Ammonium urate stones often form in Dalmations or dogs with liver dysfunction. However, up to 60 percent of this type of urolith occurs in non-Dalmation dogs and many of these do not have detectable hepatic dysfunction, as was the case with Shiloh. Unfortunately, this means that an underlying cause is not evident in this case. Control of urate stones involves feeding a diet lower in protein to reduce purine, the major amino acid involved in ammonium urate uroliths, as well as alkalinizing the urine slightly.¹

The dietary management of this case is complicated by the fact that each type of urolith requires a different pH to prevent the uroliths from re-developing. Several diets are available for control of either struvite or urate uroliths, but no diet is formulated to control both simultaneously. Royal Canin technical services reports that urate stones can develop secondary to long-term presence of struvite stones or crystals, though the underlying cause is unknown.² Thus, the decision was made to maintain Shiloh on Royal Canin Urinary S/O. It was hoped this would prevent the struvite component of the urolith from recurring and, in turn, prevent recurrence of the ammonium urate urolith.