Ureteral Stone Management: A Practical Approach
Some authors recommend metabolic evaluation in all patients even those with a single stone episode While others suggest that single stone formers without any risk factors do not require further evaluation 1. Accepted risk factors for first time stone formers include stones present in childhood, cystine, uric acid stones, multiple calculi, patients with nephrocalcinosis, stones in a solitary kidney and stones requiring surgical intervention. This risk should be discussed with all patients to give them the option of a formal metabolic evaluation versus surgical intervention at the time of stone recurrence.
It is important to weigh the cost of treatment for recurrent stones against the cost of a limited metabolic evaluation and appropriate prevention. It is obvious that in those circumstances that minimally invasive technology is not readily available or is associated with high cost, a metabolic evaluation with a hour urine collection is cost-effective. Metabolic evaluation of patients with urolithiasis can be divided into simple and more exhaustive investigations A simple evaluation includes the addition of a hour urine collection to the other blood work as discussed previously.
Urine is collected at home while patients are consuming their normal diet and prescribed medications. It is advisable to postpone the complete metabolic evaluation for at least 1 month after the resolution of ureteral obstruction or infection or after surgical intervention for stone. The hour urine collection is examined for volume, pH, calcium, uric acid, oxalate, citrate, phosphorus, sodium, and creatinine. In patients at high risk for stone recurrence family history, early age of onset, nephrocalcinosis, and associated medical conditions or a recurrent stone former, a more detailed evaluation is indicated.
Such patients may require additional hour urine collection with calcium and acid loading tests. Pak and colleagues have suggested an ambulatory protocol to differentiate subtypes of hypercalciuria This protocol includes two hour urine collections on a normal diet and another hour collection after a week of a calcium and sodium restricted diet followed by an oral calcium load test.
However, others criticize the value of calcium load test 1. A repeat urine collection after initiation of medical treatment for stone disease should be performed to evaluate treatment efficacy and to adjust medications as indicated. Any significant change in diet or medication requires repeat urine collections.
Metabolic evaluation can only be cost-effective if the results translate to appropriate medical management. Medical management of stone disease is directed toward stone prevention and in certain situations stone dissolution. Some measures are non-specific and are helpful for all stone forming patients regardless of etiology. This will decrease the concentration of urinary solutes.
Stone recurrence has been associated with failure to increase urine output. Dietary adjustments may be useful. In some patients with hypercalciuria, the intestinal absorption of calcium is increased. It has been suggested that decreasing calcium intake will decrease urinary calcium excretion. A low calcium diet may cause increased intestinal absorption of oxalate. Furthermore, bone mineral density has been shown to be below normal in most stone formers and a low calcium diet may further decrease this bone mineral density 17, In addition, in a prospective study on dietary calcium intake in a large cohort of men, higher calcium intake was associated with a lower risk of calcium stone formation These data have been supported by a more recent study showing that a cohort of stone formers had a significantly lower calcium intake than a control group Therefore, most authorities believe that a rigid dietary calcium restriction is not advisable and may be harmful 1,2,7, With regard to dietary sodium intake, it is well known that a high sodium intake inhibits tubular reabsorption of calcium, thus increasing calcium excretion.
Sodium restriction has been shown to significantly decrease urinary calcium concentration 21, Therefore, high sodium intake should be avoided in all stone formers. The main source of oxalate in the urine is endogeneous. However, in patients with calcium stones some degree of hyperoxaluria may be observed secondary to intestinal absorption. Therefore, patients may benefit from a low-oxalate diet, avoiding extensive consumption of foods such as spinach, chocolate, nuts, tea, wheat bran, and strawberries In general, a balanced diet, avoiding extremes is recommended.
Epidemiological studies have shown that the incidence of renal stones is higher in countries in which protein intake is higher A high protein intake will increase urinary calcium, oxalate and uric acid concentrations. The post-prandial acidosis associated with high protein intake may also result in hypocitraturia. Stone patients should avoid excessive protein intake.
In summary, all stone formers benefit from these general measures including increased urinary output to above 1. This however, may not be the case in an individual patient. This is supported by the fact that many patients with a documented urinary abnormality never form stones. Furthermore, many patients are found to have more than one abnormal parameter by hour urinary collection.
In the following, we will briefly review some of the general aspects of the medical management based on the metabolic evaluation. Sodium cellulose phosphate has been used as a selective medical management for absorptive hypercalciuira types I and II 2, This is a nonabsorbable ion exchange resin, which binds to calcium and inhibits calcium absorption. There are several potential side effect of sodium cellulose phosphate including negative calcium balance, hyperoxaluria and magnesium depletion. Furthermore, sodium cellulose phosphate is relatively costly.
These potential side effects have detracted from its routine use in the clinical practice.
Evaluation of emergency extracorporeal shock wave lithotripsy for obstructing ureteral stones
Therefore, hydrochlorothiazide may be used in combination with potassium citrate as the initial treatment for absorptive hypercalciuria Thiazide is the most commonly used medication for selective treatment of hypercalciuria. Thiazide acts directly on the kidney to reduce urinary calcium excretion in distal tubules and by causing volume depletion and augmenting proximal tubular reabsorption of calcium. Therefore, thiazide is the treatment of choice for renal hypercalciuria In addition, thiazide may improve bone calcium absorption and results in a positive calcium balance The increase in bone density makes thiazide the preferred treatment for treatment of hypercalciuria in patients at risk for bone disease such as post-menopausal women, children or those with osteoporosis.
In this situation, thiazide treatment may be temporary stopped and sodium cellulose phosphate administered for 6 months; thiazide treatment then may be resumed. Concomitant potassium citrate is necessary in patients on thiazide therapy to avoid hypokalemia and thiazide induced hypocitraturia. Orthophosphate is indicated in Type III absorptive hypercalciuria due to renal phosphate leak Orthophosphate decreases urinary calcium by decreasing intestinal absorption of calcium mediated by 1,25 Dihydroxy Vitamin D3.
Urinary phosphate is markedly increased during therapy; its use is therefore contraindicated in cases of infectious stones magnesium ammonium phosphate Hyperuricosuric calcium stones can be treated with allopurinol mg per day , which will decrease uric acid synthesis and lower urinary uric acid.
Potassium citrate is an effective treatment alternative for these stones. Potassium citrate may reduce the urinary saturation of calcium oxalate and inhibit urate-induced crystallization of calcium oxalate. Calcium stones due to enteric hyperoxaluria may be treated with administration of calcium after efforts to reduce diarrheal states have been tried. However, a decrease in urinary oxalate may be associated with an increase in urinary calcium concentration, which may obviate the beneficial effect of this therapy. Calcium citrate may theoretically have a role in treatment of enteric hyperoxaluria.
Calcium citrate may decrease urinary oxalate by binding to oxalate in the bowel and increase urinary pH by providing an alkali load. Patients with congenital hyperoxaluria begin stone formation in childhood and develop nephrocalcinosis. Characteristic abdominal plain x-ray appears like a renal nephrogram. However, the efficacy of this treatment is limited Hypocitrauric calcium stones may be associated with distal renal tubular acidosis, chronic gastrointestinal disease with diarrhea, secondary to thiazide treatment or idiopathic 25, In all these circumstances, potassium citrate, which may be given in crystal, liquid or tablet formulation, is an effective treatment.
The initial dose should be 60 mEq in divided doses. Correction of factors contributing to metabolic acidosis will contribute to prevention of hypocitraturic stone recurrences. Potassium citrate will correct the acidosis and hypokalemia in patients with metabolic acidosis. Furthermore potassium citrate will increase the urinary citrate level to normal range in patients with hypocitraturia Patients that are non-compliant or intolerant of pharmacological citrate supplement may increase urinary citrate levels with lemonade consumption.
Medical Management of Non-Calcalerous Stones. This will dissolve the preformed stones and prevent further stone formation or growth. In the past, this was accomplished with sodium bicarbonate or a combination of sodium and potassium alkali therapy. While sodium may cause dissociation or inhibition of uric acid formation, this may contribute to formation of calcium stones 8. Therefore, potassium citrate or potassium bicarbonate are currently the preferred medications for urinary alkalinization Since infection with urease producing organism is the main mechanism for struvite stone formation, appropriate treatment of UTIs may decrease the chance of stone growth.
Medical therapy can be attempted with the urease inhibitor acetohydroxyamic acid AHA.
This medication will decrease urinary ammonia levels with a subsequent decrease in urinary pH. However, it is associated with significant side effects such as deep venous thrombosis, and gastrointestinal side effects limiting its usefulness 11, Theoretically, acidification of urine is an effective means of preventing struvite stone formation and growth.
However, significant side effects including sepsis, hypermagnesemia, and death may occur In general, medical treatment plays a minor role for treatment and prevention of infectious stones 2. To help dilute cystine, patients have to consume large volumes during the day and night. A urinary pH of 7. Medications such as D-penicillamine and alpha-mercaptopropionylglycine Thiola can be used to increase the solubility of cystine by forming disulfide complexes.
Ureteral Stone Management
D-penicillamine is associated with significant side effects such as pancytopenia and dermatititis. Therefore, Thiola is the preferred medication Advances in endourological techniques along with the introduction of new technologies have revolutionized surgical management of urinary stone disease. Furthermore, selective medical management is effective in cases of clear metabolic abnormalities. In the future, elucidation of the exact mechanisms responsible for stone recurrences will improve our understanding of stone disease and lead towards a more effective medical management.
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Urol Clin North Am, , N Engl J Med, , Pak CY: Citrate and renal calculi: new insights and future directions. Am J Kidney Dis, , Griffith DP: Struvite stones. Kidney Int, , Singer A, Das S: Cystinuria: a review of the pathophysiology and management. Pak CY: Should patients with single renal stone occurrence undergo diagnostic evaluation? Preminger GM: The metabolic evaluation of patients with recurrent nephrolithiasis: a review of comprehensive and simplified approaches, J Urol, , Am J Med, , Nephrol Dial Transplant, , Lancet, 2: , Massey LK, Sutton RA: Modification of dietary oxalate and calcium reduces urinary oxalate in hyperoxaluric patients with kidney stones.
Though almost all urologists deal with ureteral stones, there have been many recent improvements in instrumentation and adjunctive equipment as well as improvements in imaging and the data we can obtain from radiologic imaging in order to guide stone management. Newer topics such as how to limit radiation exposure to both the patient and the urologist, the accuracy and limitations of low-dose computed tomography as well as a review of the most recent studies will be covered in this book.
Ureteral Stone Management: A Practical Approach
The purpose of this book is to provide a complete updated roadmap to treating ureteral stones, from early management decisions from information found on radiologic studies to adjusting to intra-operative challenges. Wordery is one of the UK's largest online booksellers. With millions of satisfied customers who enjoy low prices on a huge range of books, we offer a reliable and trusted service and consistently receive excellent feedback. We offer a huge range of over 8 million books; bestsellers, children's books, cheap paperbacks, baby books, special edition hardbacks, and textbooks.
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