What are they?
Bladder crystals form in urine all the time - there are loads of unwanted salts and waste materials in urine which can react together to produce them. Normally, however, they are so small that they don't cause any problems. Sometimes, however, the stones may get large enough to irritate the bladder lining, or even cause a blocked bladder - which is a medical emergency.
What causes them?
There are a number of different types of stones, each with their own set of causes. The more common ones are: (1) Struvite (also called "Triple Phosphate" or "Magnesium Ammonium Phosphate"), which are usually caused by infections, alkaline urine, or sometimes minor dietary imbalances. (2) Cystine, caused by acidic urine, usually only a problem in dogs with a particular genetic disorder. (3) Calcium Oxalate, which may be caused by a genetic disorder, abnormal calcium levels (typically in dogs with a tumour or a parathyroid disease), or antifreeze poisoning. (4) Urate, usually caused by liver disease but is normal in some breeds of dog!
What dogs are at risk?
Any dog may develop a bladder stone - most commonly struvite, triggered either by a urinary tract infection or a slight dietary imbalance. Cystine crystals are most commonly seen in breeds such as Newfoundlands, Bassets and Chihuahuas; whereas the gene causing Calcium Oxalate production is more common in the Yorkshire Terrier and Lhasa Apso (among others). Urate crystals almost always mean liver disease - except in Dalmatians, where they are a normal finding! If stones do start to form, they are unlikely to cause a blockage in bitches (whose short, wide urethra or "urine tube", is normally able to expel them). They're much more dangerous in male dogs, where they may block the urethra or become lodged in the penis bone, preventing the dog from urinating.
What are the symptoms?
The most common symptom is cystitis (although this may also be the cause, especially with Struvite!). This typically causes blood in the urine, pain and discomfort on urination, and unusually frequent production of small amounts of urine. If the bladder becomes blocked (a "Urinary Obstruction"), however, the dog will be straining to urinate without passing anything except perhaps a small amount of blood-tinged fluid. Once their bladder is full this will result in uraemic poisoning, causing depression, dehydration, vomiting, collapse and, ultimately, death if not rapidly treated.
How are they diagnosed?
We can see the crystals in urine samples when we look at it down the microscope - each type looks different so we can tell which we're dealing with (for example, Urate crystals look like spindles or spiky balls, whereas Struvite forms rectangular crystals sometimes described as being like "coffin lids"). An obstruction, however, we would usually diagnose based on the presenting signs, an overfull bladder, and evidence on blood tests of dangerously high levels of urea in the blood. Sometimes, we can see the stones in the bladder too, with ultrasound or X-rays.
How can they be treated or managed?
Many stones (Struvite, Cystine and Urate) can be dissolved with a proper diet - we recommend a commercially prepared diet that is formulated not just to prevent them from forming, but to dissolve any stones already present. However, if they are too large, or are causing an obstruction, they usually have to be removed surgically. Many stones lodged in the urethra can be flushed back into the bladder, and then we can remove them easily from there in surgery, but if not, we will have to cut into the urethra to remove them.
Can they be prevented?
If you have a dog who is prone to bladder crystals or stones, an appropriate diet is the best way to prevent them.