What are Struvite Stones? Causes, Treatments and Prevention
People usually assume that all kidney stones are made of calcium. This is not true. Some people will form kidney stones composed of different minerals and compounds. If you’re one of these unlucky folks then the usual advice for kidney stones may not pertain to you.
One of the more common types of non-calcium kidney stones are struvite stones. Sounds fancy! Unfortunately struvite stones are just as problematic, and sometimes more so, than other types of stones.
Since Dr. Google is littered with articles about struvite stones in the bladders of cats and dogs (yes this is true), we felt it was about time that a board-certified urologist provided you with some accurate information about struvite stones in humans.
We love your furry, 4-legged friends just as much as you do, but let’s focus on you right now and learn the following:
- What are struvite stones?
- What causes struvite stones in humans?
- How do you treat struvite stones?
- How do you prevent struvite stones?
Kidney stones suck. Let’s get you the information you need.
What are struvite stones?
Struvite stones are composed of ammonium magnesium phosphate. These phosphate crystals tend to form stones in an alkaline urine (more chemistry ugh) caused by chronic urinary tract infections.
Bacteria have an enzyme that turns a chemical in the urine (urea) into ammonium. The ammonium then parties up with a little phosphate, and a little magnesium, leading to struvite stones.
Struvite stones tend to get BIG. I mean real big. In fact they can completely fill up the upper plumbing pipes of the kidney leading to something called a staghorn kidney stone. This picture below shows a right-sided staghorn stone (your left) on a plain abdominal x-ray.
What causes struvite stones in humans?
As we just discussed, struvite stones tend to form because of chronic urinary tract infections. When you have recurrent infections in the kidney, the bacteria not only make you sick but they cause struvite crystals to form and grow together leading to struvite stones.
This is in contrast to most other kidney stones which are caused by:
- Dietary excess of sodium, oxalate
- Metabolic abnormalities of the kidney
Dehydration probably leads to struvite stones as well. A lack of adequate water intake makes it more likely that the struvite crystals will form into stones. More importantly, poor water intake can cause urinary tract infections.
For better or for worse, there are no foods that cause struvite stones.
What are the symptoms of struvite stones?
Struvite stones can certainly present like most other kidney stones with the most excruciating pain of your life. This occurs when the struvite stone is blocking the outflow of urine from the kidney. Typical symptoms of struvite stones include:
- Flank, back or abdominal pain
- Blood in the urine
- Difficulty urinating
In some cases however, struvite stones will silently grow in the kidney without causing any symptoms. A patient may report chronic urinary tract infection symptoms, but not have any additional symptoms from the stone. If a stone never causes an obstruction then you may not have any warning signs a struvite stone is forming.
Once it is big enough like the staghorn calculus we showed earlier, a patient may notice more of a dull flank or back pain.
How do you diagnose struvite stones?
All kidney stones require imaging to make a definitive diagnosis. Once a struvite stone is suspected based on a patient’s symptoms, then imaging should be ordered.
A plain abdominal x-ray is the quickest and cheapest option. A struvite stone will show up because of the magnesium/phosphate components of the stone. Unfortunately a plain x-ray will not give you any detail about the kidney or plumbing system.
Next a renal ultrasound can be considered. This uses sound waves to visualize the kidney for any stones or evidence of a blockage. Ultrasounds can miss struvite stones due to the limitations of this modality. You also won’t be able to see if any stones are downstream from the kidney in the ureter.
The best imaging test for struvite stones is a CT scan of the abdomen and pelvis. It is the most accurate test of the three. A CT scan shows us the following:
- Exact size and location of the struvite stone
- Health of the kidney
- Presence of hydronephrosis or obstruction of the kidney
- Any other abnormalities within the abdomen/pelvis
How do you treat struvite stones?
All else being equal, struvite stones are treated no differently than kidney stones of similar size and location.
If you have a struvite stone less than 5 mm that is working it’s way down the ureter, then a trial of stone passage is reasonable. A medication tamsulosin has been shown to increase the likelihood of stone passage. As long as an active urinary tract infection isn’t present, then tamsulosin can be prescribed with a pain medication.
Since struvite stones tend to grow larger than the average kidney stone, they may require more invasive procedures for complete removal. The most effective surgery for stones greater than 2 centimeters is a percutaneous nephrolithotomy (PCNL). This is the fancy doctor term for going in through the back to directly access the kidney.
A PCNL (see below) allows for larger instruments which can jack hammer and Hoover vacuum stone pieces. Bacteria can live within the stones, so complete removal is important. Otherwise the bacteria will continue to break down the urine chemicals leading to recurrent stones.
If a stone is a more reasonable size (< 2 cm), then more common surgeries like a shockwave lithotripsy (ESWL) or a laser endoscopy from the bladder (ureteroscopy) could be considered.
How do you prevent struvite stones?
The best method to prevent struvite stones is to prevent chronic urinary tract infections. As long as those little buggers are performing chemistry experiments with your urine, struvite stones can form. The best strategies for preventing urinary tract infections are:
- Increasing fluid intake
- Increasing frequency of urination
- Treatment of constipation
- High-quality cranberry supplements like these from Utiva Health
- Prophylactic antibiotics
There is also a medication called acetohydroxamic acid (AHA) that can prevent the creation of ammonium by bacteria. It blocks the enzyme urease which turns urea into ammonium. The main limitation of AHA is it’s side effect profile. Many patients cannot tolerate taking AHA long-term.
Struvite Stone Conclusions
Struvite stones are not your run-of-the-mill kidney stones. They can grow quite large and are usually in the setting of chronic urinary tract infections. This leads to a higher likelihood of more invasive surgeries and long-term kidney damage.
If you’re concerned that you might have a struvite stone, or if you’ve already had one, maybe it’s time you have an evaluation with a VirtuCare urologist. We can provide initial consultations or even second opinions if you need some further assurance that you’re on the right path.
Struvite stones can be a big deal. Don’t go fighting them alone. At VirtuCare, we’ve got your back! Literally and figuratively.