General Management of Urolithiasis

6. General Management of Urolithiasis

Dissolution protocols are aimed at dissolving the urolith or arresting further growth by reducing the supersaturation of urine with calculogenic substances.

Relief of Urinary Tract obstruction if Necessary

This will generally require surgical removal once the patient has been stabilized. Urethral calculi in male dogs may be flushed retrograde into the bladder prior to surgery or medical dissolution.

Elimination of Existing Uroliths

Medical Dissolution

Dietary modification may reduce intestinal absorption and urinary excretion of crystalloids and can also modulate urine pH. The balance between different nutrients (including calcium, phosphorus, sodium, acidifiers, dietary fiber and oxalate) depends on the formulation of the diet. This allows manufacturers to formulate diets that can change the urinary pH, stimulate diuresis, and reduce urinary mineral excretions, thereby assisting in the management of urinary stone diseases. Strategies vary according to stone type (see Nutritional Management). Calcium oxalate, calcium phosphate and silica uroliths cannot be dissolved medically at a physiologically useful rate and therefore need to be surgically removed before appropriate protocols to prevent recurrence are implemented (Osborne et al., 1995).

General Treatment Considerations

• Cystouroliths may be managed by medical dissolution, voiding urohydropropulsion, or cystotomy
• Ureteral and urethral stones are less amenable to medical dissolution because they are not consistently in contact with undersaturated urine. Ureteroliths, when associated with complete ureteral obstruction and hydronephrosis mandate surgical removal. Ureteroliths that are associated with partial ureteral obstruction can be managed conservatively as they may move into the bladder. With respect to urethroliths it is often possible to flush them retrograde into the bladder where they can be managed with medical dissolution
• Nephroliths maybe treated by surgical removal, although medical dissolution for struvite uroliths is a consideration. Benign neglect is possible in uninfected and non-obstructing nephroliths.

Adjunctive medical management is indicated when UTI is present, the urolith type is poorly amenable to dietary changes, or when there is further urolith growth. Certain drugs act specifically by interrupting metabolic pathways of crystalloid excretion, for example allopurinol in purine urolithiasis of Dalmatian dogs. Acidifying or alkalizing drugs can help alter urine pH.

During dissolution, uroliths become smaller and may pass into the urethra (in the male dog) or ureters, causing urinary obstruction and/or hydronephrosis. Owners should be warned about this possibility, and regular radiographic re-evaluation is required during medical dissolution of nephroliths to detect ureteral calculi before they cause hydronephrosis (Osborne et al., 1999d, Lulich et al., 2000). The dissolution process can last from 1 to 6 months.

Mechanical Removal

Surgery is indicated for stone types that are not or poorly amenable to medical dissolution and too large to be voided through the urethra, or when they are causing urinary obstruction. It is also required in dogs with anatomic defects of the urinary tract (e.g., bladder diverticulum) that predispose to UTI; in these cases stone removal can be combined with correction of the defect. Surgery alone is associated with a high rate of recurrence, since it does not correct the underlying factors causing urolithiasis and because it may be difficult to remove very small stones or fragments, which can later function as a nidus for further stone formation (Lulich et al., 2000). Post-operative imaging is necessary to ensure that all calculi have been removed.

The general aim of dietary management of urolithiasis is to reduce supersaturation of urine with calculogenic substances by:

• Increasing water intake and thus urine volume to decrease urine crystalloid concentration
• Altering the urine pH to increase the solubility of crystalloids in the urine
• Changing the diet to decrease the quantity of crystalloids excreted in the urine

Small uroliths in the bladder and/or urethra can sometimes be removed during voiding urohydropropulsion or cystoscopy (Osborne et al., 1999e).

Lithotripsy has recently been described as a means of fragmenting uroliths. Fragmentation of renal and ureteral uroliths using electrohydraulic or extracorporeal shock-wave lithotripsy has been documented in a small number of dogs (Block et al., 1996; Adams et al., 1999). Laser lithotripsy has been reported effective in fragmenting bladder uroliths (Davidson et al., 2004). However, all these techniques have limited availability.

Eliminate Miscellaneous Risk Factors

- Acidifying diets are useful in preventing struvite urolithiasis but should be avoided in dogs with urate urolithiasis.
- Treatment of UTI is mandatory to reduce the risk of struvite urolith formation.
- Treat underlying diseases that may potentiate urolithiasis (e.g., hyperparathyroidism, hyperadrenocorticism).

Prevention of Recurrence

- Correct underlying causes
- Minimize risk factors (dietary adaptation)
- Increase diuresis and reduce urinary supersaturation
Struvite uroliths are generally sensitive to medical dissolution using a calculolytic diet in association with antibiotic therapy.