Canine Urolithiasis: Which Diet is Appropriate?

General information
Urolithiasis is a common disorder of the urinary tract in dogs. It may be a first indication for underlying systemic disorders such as a portosystemic shunt. Detection of uroliths is therefore the first step into the diagnostic process. Determination of urolith composition is of high importance for further diagnostics, treatment and prevention.

Urolith formation is initiated by the formation of a crystal nidus. This requires supersaturation of the urine with lithogenic compounds as well as other factors (e.g. pH, presence of crystallization inhibitors and/or promotors, a preformed organic matrix). The presence of foreign materials (e.g. catheters, suture material) may also enhance nucleus formation. After formation of the nidus, the crystals will grow. This depends on: being present in the urinary tract, degree and duration of supersaturation, physical characteristics of the nidus. Epitaxy may occur (i.e. growth of a crystal on the nidus which has a different mineral composition). 

History
Owners often notice hematuria, pollakiuria, dysuria and sometimes incontinence. If an obstruction and/or concomitant bacterial infection are present restlessness, lethargy and vomiting may be noted. A dietary history is important to identify risk factors such as vitamin-mineral supplements, use of unconven- tional diets. Also medication and previous illnesses may predispose the patient to various types of uroliths.

Clinical signs
Apart from the signs that the owner has noticed abdominal pain may be noted. Especially in patients with nephroliths, no clinical signs may be present. Uroliths may be palpable in the urethra by rectal examination. Inability to advance a catheter through the urethra may indicate the presence of uroliths, however, this could also be caused by strictures, or space-occupying lesions that occlude the urethral lumen. Pain and enlargement of the kidney may be noted.

Diagnostics
Urinalysis may reveal signs of inflammation and/or infection. Urinary pH may be increased due to infection, but can also be increased after a meal. Culture with antimicrobial susceptibility testing is always recommended. Crystalluria may be present and is indicative for supersaturation. It can also be an in vitro effect with no clinical importance. To prevent these errors a urine specimen should be evaluated when it is still fresh and warm. Only quantitative analysis of uroliths reveals their true composition; however crystals may provide a tentative diagnosis. Radiographs may reveal the site, number, density and shape of radiodense uroliths. Ultrasound reveals the same information for both radiodense and radiolucent uroliths. Small uroliths may only be detected by double-contrast radiography. Blood biochemistry may reveal the presence of liver failure and hypercalcemia. Uroliths must be retrieved, either by spontaneous voiding, urohydropropulsion, catheter-assisted or by surgery and send in for quantitative analysis.  [...]