Dissolution of struvite stones with ascorbic acid

Abstract

This case report describes an elderly man with a history of recurrent urinary tract infections and obstructive pyelonephritis with struvite stones caused by Proteus mirabilis. Despite appropriate antibiotic treatment, the stones increased in size, necessitating alternative therapy. This case highlights the use of ascorbic acid to lower the urine pH, which contributes to the dissolution of struvite stones. Dual-energy CT was used to differentiate the stone composition for the initiation of ascorbic acid. These findings suggest that ascorbic acid can accelerate struvite stone dissolution, and that dual-energy CT is valuable for both initial diagnosis and follow-up.

1 Introduction

Struvite stones, also known as infection stones, are a type of kidney stone that forms in the presence of urease-producing bacteria such as Proteus mirabilis . These bacteria cause urine to become alkaline, leading to the precipitation of magnesium ammonium phosphate (struvite) crystals. Struvite stones are challenging to treat due to their rapid growth and recurrence, often requiring urological intervention. Traditional antibiotic therapy is essential for managing the underlying infection but generally ineffective in dissolving stones. Acetohydroxamic acid inhibits stone growth, but its side effects limit its use. Although the use of ascorbic acid is controversial because of the potential risk of forming other types of stones, particularly calcium oxalate stones, ^, it theoretically has the potential to dissolve struvite stones. Additionally, when collecting stones is difficult, dual-energy CT (DECT) effectively identifies compositions, providing key insights for targeted treatment without requiring crystallography. Here, we describe a case in which struvite stones, identified by DECT, were successfully dissolved using ascorbic acid.

2 Case presentation

An elderly man in his 80s residing in a nursing home presented with fever, rigors, and back pain. He had no family history of urolithiasis or recurrent stones. A CT scan two years prior showed two right kidney stones and three left, the largest measuring 6.0 mm. Three months before this presentation, the patient was admitted for left obstructive pyelonephritis due to an 8.6 mm ureteral stone and a right kidney stone of 6.0 mm. The patient was treated with a double-J stent and effective antibiotics. Proteus mirabilis was detected in both blood and urine cultures. The patient was discharged after two weeks of antibiotics. A CT scan ten days before admission showed a residual left ureteral stone of 4.6 mm and a right kidney stone, the largest now 11.0 mm. Although asymptomatic, urinalysis revealed a pH of 8.0 and struvite crystals. He presented with a temperature of 39.3 °C and tenderness in the right costovertebral angle. Laboratory values showed a WBC count of 9800/μL, creatinine at 1.78 mg/dL, and CRP at 1.51 mg/dL. Urinalysis indicated a pH of 7.5, with WBC >100/HPF and the presence of struvite crystals. Gram stain of the urine revealed granulocytes and phagocytosis of Gram-negative bacilli. The overall clinical course of the patient is illustrated in Fig. 1 . DECT performed on the day of admission showed right hydronephrosis due to right ureterolithiasis, bilateral kidney stones, and left ureterolithiasis ( Fig. 2 ), with a DJ stent already in place on the left side. The right kidney stone had enlarged from 11.0 mm to 15.2 mm in just ten days ( Fig. 2 A and C, dashed arrows). While almost all of the struvite stones appeared hazy ( Fig. 2 A-D, dashed arrows), the left kidney stone ( Fig. 2 E, white arrow) and left ureteral stone ( Fig. 2 F, arrowhead) were dense. Zeff from DECT suggested the right kidney stone and ureteral stone were struvite ( Fig. 3 ). Right obstructive pyelonephritis was diagnosed, and a DJ stent was placed. Urine cultures from the bladder and right renal pelvis were positive for Proteus mirabilis . Although stone analysis was not performed due to the absence of passed stones, high urine pH, detection of Proteus mirabilis , and DECT findings led to the diagnosis of struvite stones. Blood and urine test results did not support the presence of other stone types. Given the rapid size increase over the previous ten days and the acute phase of infection, we opted for an emergency intervention with the administration of cefmetazole 1 g twice daily and DJ stenting, with the intention of performing ureteroscopy after the patient’s condition stabilized. High-dose ascorbic acid (>1000 mg/day) was avoided due to the risk of calcium oxalate stones; instead, ascorbic acid 200 mg three times a day was started on day 2. CT on day 12 revealed most stones had disappeared or reduced in size, except for two left renal stones: one remained at 2.3 mm, while the other increased from 3.6 mm to 7.0 mm ( Fig. 1 ). The urine pH decreased from 8.5 on day 2 to 7.5 on day 12, showing only a limited reduction. This is likely due to the neutralization effect caused by the ongoing dissolution of the stones. Given the dramatic dissolution of most stones within just ten days, we considered the potential benefits of continued vitamin C administration to be minimal, while the observed increase in the size of one stone suggested a higher risk of adverse effects. Therefore, at the time of discharge, we decided to discontinue vitamin C and switch to cranberry juice, which was considered a safer alternative for the prevention of stone recurrence. Retrospective DECT analysis suggested the remaining left kidney stone was uric acid ( Fig. 4 A and B), while the dissolved left ureteral stone was brushite ( Fig. 4 C and D). He was treated with antibiotics for three weeks: two weeks of IV therapy (cefmetazole 1 g twice daily for four days and ampicillin 2 g four times daily for ten days) during hospitalization, followed by one week of oral amoxicillin 500 mg three times daily post-discharge. CT two months later showed the sizes of the two remaining left renal stones were unchanged, while all other stones had disappeared ( Fig. 5 A). Based on this finding, the bilateral DJ stents were removed without ureteroscopy. The residual left kidney stone was suggested to be uric acid based on Zeff ( Fig. 5 B and C). The patient had no recurrence of pyelonephritis or ureteral stones nine months post-discharge.