Материал: Oxford American Handbook of Urology ( PDFDrive )

EVALUATION OF THE STONE FORMER 367

Table 8.2 Characteristics of stone types

* Urine pH must be above 7.2 for deposition of struvite crystals.

Urine pH

Urine pH in normal individuals shows variation, pH 5–7. After a meal, pH is initially acid because of acid production from metabolism of purines (nucleic acids in, for example, meat). This is followed by an alkaline tide, with pH rising to >6.5.

Urine pH can help establish what type of stone the patient may have (if a stone is not available for analysis) and can help the urologist and patient in determining whether preventative measures are likely to be effective or not.

•pH <6 in a patient with radiolucent stones suggests the presence of uric acid stones.

•pH consistently >5.5 suggests type 1 (distal) RTA (~70% of such patients will form calcium phosphate stones).

Evaluation for RTA

Evaluate for RTA if there are calcium phosphate stones, bilateral stones, nephrocalcinosis, MSK, or hypocitraturia.

-If fasting morning urine pH (i.e., first urine of the day) is >5.5, the patient has complete distal RTA.

-First and second morning urine pH is a useful screening test for detection of incomplete distal RTA; over 90% of cases of RTA have a pH >6 on both specimens. The ammonium chloride loading test involves an oral dose of ammonium chloride (0.1 g/kg; an acid load). If serum pH falls <7.3 or serum bicarbonate falls <16 mmol/L, but urine pH remains >5.5, the patient has incomplete distal RTA.

Diagnostic tests for suspected cystinuria

These include the cyanide-nitroprusside colorimetric test (cystine spot test). If positive, a 24-hour urine collection is done. A 24-hour cystine >250 mg is diagnostic of cystinuria.1

1 Millman S, Strauss AL, Parks JH, Coe FL (1982). Pathogenesis and clinical course of mixed calcium oxalate and uric acid nephrolithiasis. Kidney Int 22:366–370.

368 CHAPTER 8 Stone disease

Kidney stones: presentation and diagnosis

Kidney stones may present with symptoms or be found incidentally during investigation of other problems. Presenting symptoms include pain or hematuria (microscopic or occasionally macroscopic). Struvite staghorn calculi classically present with recurrent UTIs. Malaise, weakness, and loss of appetite can also occur.

Less commonly, struvite stones present with infective complications (pyonephrosis, perinephric abscess, septicemia, xanthogranulomatous pyelonephritis).

Diagnostic tests

-Plain abdominal radiography: Calculi that contain calcium are radiodense. Sulfur-containing stones (cystine) are relatively radiolucent on plain radiography.

-Radiodensity of stones in decreasing order is calcium phosphate > calcium oxalate > struvite (magnesium ammonium phosphate) >> cystine.

-Completely radiolucent stones (e.g., uric acid, triamterene, indinavir) are usually suspected on the basis of the patient’s history and/or urine pH (pH <6: gout; drug history: triamterene, indinavir), and the diagnosis may be confirmed by ultrasound, computed tomographic urography (CTU), or magnetic resonance urography (MRU).

-Renal ultrasound: Its sensitivity for detecting renal calculi is ~95%.1

A combination of plain abdominal radiography and renal ultrasonography is a useful screening test for renal calculi.

-IVP is increasingly being replaced by CTU. IVP is useful for patients with suspected indinavir stones (which are not visible on CT).

-CTU is a very accurate method of diagnosing all but indinavir stones. It allows accurate determination of stone size and location and good definition of pelvicalyceal anatomy.

-MRU cannot visualize stones but is able to demonstrate the presence of hydronephrosis.

1 Haddad MC, Sharif HS, Abomelha ME, et al. (1992) Management of renal colic: redefining the role of the urogram. Radiology 184:35–36.

370 CHAPTER 8 Stone disease

Kidney stone treatment options: watchful waiting

The traditional indications for intervention are pain, infection, and obstruction. Hematuria caused by a stone is only very rarely severe or frequent enough to be the only reason to warrant treatment.

Before embarking on treatment of a stone that you think is the cause of the patient’s pain or infections, warn the patient that though you may be able to remove the stone successfully, their pain or infections may persist (i.e., the stone may be coincidental to their pain or infections, which may be due to something else).

Remember, UTIs are common in women, as are stones, and it is not therefore surprising that the two may coexist in the same patient but be otherwise unrelated.

Options for stone treatment are watchful waiting, extracorporeal shock wave (ESWL), flexible ureteroscopy, percutaneous nephrolithotomy (PCNL), open surgery, and medical dissolution therapy.

When to watch and wait—and when not to

It is not necessary to treat every kidney stone. As a rule of thumb, the younger the patient, the larger the stone, and the more symptoms it is causing, the more inclined we are to recommend treatment.

Thus, one would probably do nothing about a 1 cm asymptomatic stone in the kidney of a 95-year-old patient. On the other hand, a 1 cm stone in an asymptomatic 20-year-old runs the risk over the remaining (many) years of the patient’s life of causing problems. It could drop into the ureter, causing ureteric colic, or it could increase in size and affect kidney function or cause pain.

Asymptomatic stones followed over a 3-year period are more likely to require intervention (surgery or ESWL) or to increase in size or cause pain if they are >4 mm in diameter and if they are located in a middle or lower pole calyx.1 The approximate risks, over 3 years of follow-up, of requiring intervention, of developing pain, or of increase in stone size, relative to stone size, is shown in Table 8.3.

Another factor determining the need for treatment is the patient’s job. Airline pilots are not allowed to fly if they have kidney stones, for fear that the stones could drop into the ureter at 30,000 ft, with disastrous consequences.

Some stones are definitely not suitable for watchful waiting. Untreated struvite (i.e., infection related) staghorn calculi will eventually destroy the kidney if untreated and are a significant risk to the patient’s life. Watchful waiting is therefore NOT recommended for staghorn calculi unless patient comorbidity is such that surgery would be a higher risk than watchful waiting.

1 Burgher A, et al. (2004). Progression of nephrolithiasis: long-term outcomes with observation of asymptomatic calculi. J Endourol 18:534–539.

KIDNEY STONE TREATMENT OPTIONS: WATCHFUL WAITING 371

Table 8.3 Approximate 3-year risk of intervention, pain, or increase in stone size

Historical series suggest that ~30% of patients with staghorn calculi who did not undergo surgical removal died of renal-related causes—renal failure and urosepsis (septicemia, pyonephrosis, perinephric abscess).2,3 A combination of a neurogenic bladder and staghorn calculus seems to be particularly associated with a poor outcome.4

2 Blandy JP, Singh M (1976). The case for a more aggressive approach to staghorn stones. J Urol 115:505–506.

3 Rous SN, Turner WR (1977). Retrospective study of 95 patients with staghorn calculus disease. J Urol 118:902.

4 Teichmann J (1995). Long-term renal fate and prognosis after staghorn calculus management. J Urol 153:1403–1407.