Canine Cystine Uroliths

Cystinuria is an inborn error of metabolism characterized by abnormal transport of cystine (an amino acid), and other amino acids by the renal tubules.  The exact mechanism of abnormal transport is unknown.

Medical and dietary protocols for dissolution of cystine uroliths have been studied and found to be effective.  These involve:

• Perform diagnostic studies including contrast radiography to identify urolith size and location, as well as confirmation of urolith composition prior to attempting dissolution.

• Initiate therapy with calculolytic diet that promotes alkaline urine, promotes diuresis,  and is restricted in protein.

• Initiate therapy with n-(2-mercaptoropionyl)-glycine (2-MPG) (Thiola) at an approximate dosage of  30mg/kg/day in 2 subdoses.

• Monitor response to therapy at appropriate intervals.

Because cystinuria is an inherited metabolic defect, and because cystine uroliths recur in a high percentage of stone-forming dogs within 1 year after surgical removal, prophylactic therapy should be considered.  We suggest:

• Utilizing protein restricted, alkalinizing diets long term.

• If necessary, further alkalinization to maintain urine pH about 7.5 may be necessary.

If diet alone is ineffective for prevention, some investigators further recommend long term therapy with 2-MPG  in a sufficient quantity to maintain a urine concentration of cystine below 200mg/L.  (Approximate dosage range =  10 to 30 mg/kg/day)

If uroliths should recur despite control of risk factors, they may be removed non-surgically by voiding urohydropropulsion if detected early.  Uroliths removed by voiding urohydropropulsion should be quantitatively analyzed.  If attempts at dissolution or non-surgical urolith removal are unsuccessful, surgery remains a reliable way to remove active uroliths from the urinary tract.  We emphasize, however, that surgery may be unnecessary for clinically inactive cystine uroliths. 

All prevention recommendations should be adjusted to meet individual patient's needs.  We recommend follow-up urinalyses, serum chemistry profiles, and radiographs on a periodic basis.