Cystinuria in Mastiffs
When someone has Cystinuria their kidneys cannot properly reabsorb the amino acids cystine, ornithine, lysine, and arginine (COLA) back into the body and the concentration of these amino acids in the urine increases. Cystine is not very soluble, so elevated levels in the urine can lead to cystine precipitation into crystals. The solubility of cystine decreases as the pH is lowered, so cystine is even less soluble in acidic urine.
As the crystals become larger they can form into cystine stones. When these crystals and stones pass through the urinary tract it can be extremely painful and when the urinary tract becomes blocked it can be a serious and life threatening problem
Cystinuria is an inherited metabolic disorder that can cause stones to form in the kidneys and urinary tract of affected individuals.
Treatment of Canine Cystinuria
My dog has been diagnosed with cystinuria. What treatment is there for this condition?
There is no treatment for cystinuria. It's an incurable genetic defect of the kidneys. However, just because your dog has cystinuria does not mean he will form stones. It appears that many, perhaps even the majority, of dogs with cystinuria do not form stones. It is not clear what the difference is between stone-formers and non-stone-formers, but at this time the difference is not believed to be one of diet or other environmental factors. There are probably genetic factors involved.
If your dog has cystinuria, you must watch him carefully for any signs of urinary obstruction: Frequent urination, blood in the urine, frequent urinary tract infections, difficult urination, scanty urination, dribbling urination, evidence of pain when urinating, a reluctance to urinate, or anything at all about their urinary habits that doesn't seem totally normal.
You then have to make sure that you obtain veterinary care from a veterinarian who knows that cystine stones are not always able to be seen in an x-ray (although they might be seen), or on an ultrasound. Sometimes it's necessary to do a procedure called a contrast study to be sure that no stones are present. For more information, read the section on the Diagnosis of Canine Cystinuria.
My dog has formed stones. Is there a treatment for that?
YES! And it's not optional. You have to get those stones out of there and treat or prevent any urinary obstruction. This is a life-threatening condition.
The most urgent need is to unblock the urinary tract if it's obstructed. This can be done with a technique known as retrograde hydropulsion, which will attempt to push any stones blocking the urethra back into the bladder. This will relieve the immediate obstruction, however, the stones in the bladder still need to be treated. This is usually done with a procedure known as a cystotomy, where the stones are removed from the bladder surgically.
If the hydropulsion does not work, an alternative urinary tract will have to be created. The preferred surgery is known as a scrotal urethrostomy, where a new opening for urination is created between the dog's penis and scrotum. This is difficult, complicated surgery and should be done by a board certified surgeon. It is expensive and the recovery period can be bloody, although in recent years new techniques have been developed that have reduced the bleeding. A cystotomy will also be performed to remove the stones in the bladder. There is a complete description of both cystotomy and retrograde hydropulsion here.
If the hydropulsion is successful and surgery is not an option or needs to be delayed, it is possible to dissolve the stones with the drug Thiola (tiopronin). Although thiola is usually well-tolerated by dogs, it is very expensive in the dosages needed for larger dogs.
Another drug, much less expensive, is penicillamine. Although it can cause more side effects than thiola, if your dog tolerates it, it may be a better choice. However, both these drugs have the potential to cause serious side effects.
Can I dissolve cystine stones with diet?
No, they cannot be dissolved with diet or supplementation.
Once my dog's stones are treated, can I prevent more from forming in the future?
Some veterinarians, including many well-known kidney specialists, feel strongly that cystine stones can be prevented, or the incidence greatly reduced, by feeding ultra-low-protein diets (such as Hills u/d) and alkalinizing the urine with drugs or supplements. Other veterinarians believe that diet is of minimal or no use in controlling the formation of stones, and that only the drug Thiola is effective for this purpose. You can read some intriguing research on this subject here.
On the Canine Cystinuria email list, most of us have found that diet and urinary alkalinization have failed to prevent our dogs from forming stones, and have sometimes caused other problems, including other types of stones that form in alkaline urine. Some of us are also concerned about feeding ultra-low-protein diets to dogs, particularly giant breed dogs, and dogs of breeds prone to cardiomyopathy.
Unfortunately, thiola is very expensive, prohibitively so for most owners of large dogs. For this reason, many owners of dogs with cystinuria who form stones opt for a scrotal urethrostomy even if their dog is not obstructed, because with this procedure, male dogs will tend to pass stones the way female dogs do, and the risk of obstruction is reduced, or even eliminated. (Female dogs with cystinuria rarely get a urinary obstruction from stones.) There is a description of this procedure toward the end of the page here.
All of us with dogs with cystinuria who form stones wish there was a simple way to treat or prevent these stones with diet or an accessible, affordable drug, but as of today that is not the case.