Laura L. Swanson

Analysis of 77,000 Canine Uroliths: Perspectives from the Minnesota Urolith Center

Of the hundreds of minerals that are found in the earth, most canine uroliths are comprised of only six types: (1) magnesium ammonium phosphate, (2) calcium oxalate, (3) calcium phosphates, (4) ammonium urate and other salts or uric acid, (5) cystine, or (6) silica. Each type has characteristics that allow its identification. During the past two decades, the prevalence of calcium oxalate canine uroliths has dramatically increased, while struvite has decreased. The most effective treatment and prevention protocols are based on knowledge of the primary mineral type comprising the urolith.

Canine and Feline Nephrolithiasis: Epidemiology, Detection, and Management

Calcium oxalate (39%) and struvite (33%) were the predominant mineral types in canine nephroliths submitted to the Minnesota Urolith Center. Urate salts (12%) and calcium phosphate (2%) occurred less frequently. Provided they are not causing obstruction, struvite nephroliths may be dissolved with medical protocols. Although there are no dissolution protocols for nephroliths containing calcium, risk-benefit ratios should be considered before proceeding with surgery.

Epidemiology of Canine Calcium Oxalate Uroliths: Identifying Risk Factors

Calcium oxalate uroliths are most commonly encountered in Miniature Schnauzers, Lhaso Apsos, Yorkshire Terriers, Bichons Frises, Shih Tzus, and Miniature Poodles. They are more common in males than females, and more common in older than young dogs. Dogs that form abnormal nephrocalcin are also predisposed to calcium oxalate uroliths. Dietary risk factors for calcium oxalate uroliths include excessive calcium supplementation or excessive calcium restriction, excessive oxalic acid, high protein, high sodium, restricted phosphorus, restricted potassium, and restricted moisture (dry formulations). Dogs with hyperadrenocorticism or hypercalcemia are predisposed to calcium oxalate urolith formation.

MEDICAL DISSOLUTION AND PREVENTION OF CANINE STRUVITE UROLITHIASIS Twenty Years of Experience

Two types of canine struvite uroliths have been recognized: infection-induced struvite is the most common type; sterile struvite is uncommonly recognized. Infection-induced struvite is most commonly associated with urease-producing staphylococcal UTI. For dogs that qualify, medical dissolution is an effective method of treatment. Medical dissolution protocols encompass: (1) eradication or control of UTI; (2) use of calculolytic diets; and (3) administration of urease inhibitors to patients with persistent UTI caused by urease-producing microbes.

Canine Cystine Urolithiasis: Cause, Detection, Treatment, and Prevention

Cystine uroliths are a sequela to cystinuria, an inherited renal tubular defect in reabsorption of cystine and some other amino acids. At the Minnesota Urolith Center, 67 breeds of dogs were identified, including English Bulldogs, Dachshunds, Mastiffs, and Newfoundlands. In some dogs, the severity of cystinuria may decline with advancing age. Current recommendations for dissolution of cystine uroliths include various combinations of diet modification, diuresis administration of 2-MPG, and alkalinization of urine.

Voiding urohydropropulsion. Lessons from 5 years of experience.

Voiding urohydropropulsion is a nonsurgical method of removing uroliths from the urinary bladder. Any urocystolith of sufficient size to pass through the distended urethral lumen can be safely and effectively removed by this technique. Compared to cystotomy, voiding urohydropropulsion offers several advantages: urolith removal can be performed in minutes, anesthetic period is shorter, postprocedural dysuria and hematuria are less severe, and it provides greater success for complete removal of small urocystoliths. This technique is not suitable for removal of large urocystoliths or uroliths that become lodged in the urethral lumen.

Rate and frequency of recurrence of uroliths after an initial ammonium urate, calcium oxalate, or struvite urolith in cats.

OBJECTIVE To determine frequency of and interval until recurrence after initial ammonium urate, calcium oxalate, and struvite uroliths in cats and whether breed, age, or sex was associated with increased risk for urolith recurrence. DESIGN Case-control study. ANIMALS 4,435 cats with recurrent uroliths. PROCEDURES To identify recurrence of uroliths in cats for which uroliths were submitted for analysis at the Minnesota Urolith Center in 1998, the facilitys database was searched for urolith resubmissions from the same cats between 1998 and 2003. Risk factors and differences in mean interval until recurrence were assessed. RESULTS Of 221 cats with ammonium urate uroliths in 1998, 29 (13.1%) had a first and 9 (4.1%) had a second recurrence. Mean interval until recurrence was 22 and 43 months for the first and second recurrence, respectively. Of 2,393 cats with calcium oxalate uroliths in 1998, 169 (7.1%) had a first, 15 (0.6%) had a second, and 2 (0.1%) had a third recurrence. Mean interval until recurrence was 25, 38, and 48 months for the first, second, and third recurrence, respectively. Of 1,821 cats with struvite uroliths in 1998, 49 (2.7%) had a first and 3 (0.2%) had a second recurrence. Mean interval until recurrence was 29 months for first and 40 months for second recurrences. CONCLUSIONS AND CLINICAL RELEVANCE These results provided insights into the frequency of urolith recurrence in cats. Because some uroliths associated with recurrent episodes probably were not submitted to our facility, our data likely represented an underestimation of the actual recurrence rate.

Canine Silica Urolithiasis: Risk Factors, Detection, Treatment, and Prevention

Uroliths containing 70% or greater silica comprise approximately 1% of the canine uroliths submitted to the Minnesota Urolith Center. Male dogs are far more commonly affected than females. In our series, 84 different breeds were affected. Currently available data suggest dietary factors play a role in their formation. Diagnosis is facilitated by the characteristic jackstone configuration of silica uroliths, but must be confirmed by quantitative analysis. Voiding urohydropropulsion or surgery are currently the most practical methods of removal of silica uroliths.