What is the diagnosis and treatment for a Struvite (magnesium ammonium phosphate) stone?

From the Guidelines

Struvite stones should be treated with complete surgical removal, usually through percutaneous nephrolithotomy (PCNL) or ureteroscopy, along with antibiotics targeting the specific bacteria, to prevent recurrence and preserve kidney function 1. The goal of treatment is to eradicate the causative organisms, relieve obstruction, prevent further stone growth, and preserve kidney function. Struvite stones are often associated with urinary tract infections caused by urease-producing bacteria, which can lead to the formation of large, branched stones. Some key points to consider in the management of struvite stones include:

• Complete stone removal is essential to prevent recurrence and preserve kidney function 1
• Antibiotics targeting the specific bacteria are crucial both before and after surgery to prevent recurrence 1
• Long-term prevention includes maintaining adequate hydration, treating urinary tract infections promptly, and using urease inhibitors like acetohydroxamic acid in some cases 1
• Regular urine testing to monitor pH levels and bacterial presence is important to detect any potential recurrence or infection 1
• Patients with anatomical abnormalities of the urinary tract or those with neurogenic bladder are at higher risk and may require more intensive monitoring 1 It is also important to note that dietary modifications play a less significant role in the prevention of struvite stones, as infection is the primary cause. However, increasing fluid intake to achieve at least 2 L of urine per day can help prevent recurrent nephrolithiasis 1.

From the FDA Drug Label

Acetohydroxamic acid has been evaluated clinically in patients with urea-splitting urinary infections, often accompanied by struvite stone disease, that were recalcitrant to other forms of medical and surgical management. The usefulness of reducing ammonia levels and decreasing urinary pH is suggested by single (not yet replicated) clinical trials in which urease inhibition 1) allowed successful antibiotic treatment of urea-splitting Proteus infections after surgical removal of struvite stones in patients not cured by 3 months of antibacterial treatment alone, and 2) reduced the rate of stone growth in patients who were not candidates for surgical removal of stones.

Struvite Stone Treatment: Acetohydroxamic acid (AHA) may be useful in the treatment of struvite stone disease by reducing ammonia levels and decreasing urinary pH, which can help to:

• Allow successful antibiotic treatment of urea-splitting Proteus infections after surgical removal of struvite stones
• Reduce the rate of stone growth in patients who are not candidates for surgical removal of stones 2

From the Research

Definition and Formation of Struvite Stones

• Struvite stones are a type of infection stone that accounts for 10-15% of all urinary calculi 3, 4.
• They are composed of struvite and/or carbonate apatite and are formed in the presence of urease-producing bacteria 4.
• The formation of struvite stones requires a urease-positive urinary tract infection, which splits urea into ammonia and CO2, leading to the formation of struvite and carbonate apatite crystals 4.

Treatment and Management of Struvite Stones

• The three key principles of treating struvite stones are: removal of all stone fragments, the use of antibiotics to treat the infection, and prevention of recurrence 3.
• Percutaneous nephrolithotomy (PCNL) is considered the gold-standard approach to treating struvite calculi, but adjuncts such as urease inhibitors, acidification therapy, dissolution therapy, extracorporeal shockwave lithotripsy, ureteroscopy, and anatrophic nephrolithotomy may be used when deemed necessary 3, 5, 6.
• Antibiotic therapy is essential in treating the underlying infection, and stone culture or urine culture from the renal pelvis at the time of surgery is necessary to guide antibiotic selection 3.
• Combined endourologic and medical treatment can achieve long-term results comparable to standard operative intervention 5, 6.

Predictors of Unfavorable Clinical Outcome

• Independent predictors of stone activity, including stone recurrence or stone-related events, include the presence of residual stones >0.4 cm2, preoperative large stone burden (>10 cm2), and the presence of medical comorbidities 6.
• Initial large stone burden, residual stones after surgery, and associated medical comorbidities may have a deleterious effect on stone recurrence or residual stone-related events 6.

Importance of Follow-up and Medical Management

• Regular surveillance and antibiotic prophylaxis are essential in preventing stone recurrence and maintaining kidney function 5, 6.
• Patients with residual fragments may demonstrate no evidence of stone growth on medical therapy, and kidney function can be maintained with careful follow-up and medical management 6.