Urolithiasis

Background

Types
- Calcium (75%)
  - Hyperparathyroidism, hypercalcemia of malignancy, sarcoidosis, increased absorption, thiazides, IBD
- Struvite (magnesium-ammonium-phosphate) (15%)
  - Proteus, klebsiella, pseudomonas, staph
- Uric Acid (10%)
  - 25% of pts w/ gout develop kidney stones

If unrelieved, irreversible renal damage occurs within 3 weeks with complete obstruction. During acute obstruction, most patients have no rise in serum creatinine because the unobstructed kidney functions at up to 185% of its baseline capacity. A rise in serum creatinine in acute obstruction suggests a solitary kidney or preexisting renal disease such that the unobstructed kidney is unable to compensate completely. Fortunately, most patients have incomplete ureteral obstruction, and many patients can be safely observed over weeks. Irreversible renal damage from an obstructive kidney stone is rare if obstruction has not been present for >1 month.

Clinical Features

acute onset of a crampy intermittent pain that originates in the flank and radiates toward the groin. As pain originates from a hollow viscus (ureter), the pain is visceral in nature without associated peritoneal irritation. Patients writhe in pain, unable to find a position of comfort. However, patients with renal colic may demonstrate rebound tenderness (29%), guarding (61%), and rigidity (8%).13 Pain is commonly accompanied by nausea and vomiting (50%). The adrenergic response to pain can result in tachycardia, hypertension, and diaphoresis. Hematuria is present in approximately 85% of patients with renal colic, whereas only 30% have gross hematuria.

The location of the pain correlates somewhat with the location of the stone. Stones in the upper ureter refer pain to the flank, whereas those in the mid-ureter radiate to the lower anterior quadrant of the abdomen. A distal ureter stone, which is where 75% of stones are diagnosed, refers pain to the groin. Stones positioned at the UVJ can mimic a urinary tract infection (UTI) by causing frequency, urgency, and dysuria in 3% to 24% of patients.13

During the interview, elucidate three separate items of history. Ask about risk factors for stone development (Table 97-1), risk factors for a poor stone-related outcome, and risk factors for important mimickers. The risk factors for a poor outcome with stones include three categories: renal function is at risk (diabetes, hypertension, preexisting renal insufficiency, single kidney or transplant), history of difficulty with stones (extractions, stents, ureterostomy tubes), and infection (fever, systemic illness, and UTI symptoms; Table 97-2). Two mimickers that are very important to exclude are abdominal aortic aneurysm (AAA) and renal artery infarction. Nephrolithiasis is the most common misdiagnosis given to patients with a rupturing or expanding AAA. Recall that stones don't usually present in men older than age 60 and do not cause hypotension, even transiently. Renal artery thrombosis can mimic stone symptoms due to swelling of the infarcted kidney and can also be associated with hematuria. However, early in the course, CT will not necessarily show inflammation around the kidney, and, because no contrast is used, the function of the kidney is not assessed.

Important Historical Features for Poor Outcome with Stone Renal function at risk Diabetes Hypertension Renal insufficiency Single kidney Horseshoe kidney Transplanted kidney History of difficulty with stones Extractions Stents Ureterostomy tubes Lithotripsy Symptoms of infection Fever Hypotension Systemic illness Urinary tract infection

Diagnosis The laboratory evaluation centers on evaluating for infection, kidney dysfunction, and possibility of pregnancy. Test all females of childbearing potential for pregnancy when considering renal colic.

Urinalysis is needed to rule out infection. If infection is found, obtain urine culture and sensitivities, as requirement for antibiotic therapy may be prolonged,14 and sensitivities help guide therapy if the empiric antibiotic fails.

Although 10% to 15% of patients with nephrolithiasis will have no hematuria, approximately 24% of patients with flank pain and hematuria have no radiographic evidence of ureterolithiasis.15 Therefore, although hematuria may contribute to diagnostic decision making, it should not be used alone to exclude or confirm the diagnosis of ureterolithiasis.15

Check renal function with both blood urea nitrogen and creatinine level, as the overwhelming majority of stone formers have reduced creatinine clearance.16 These studies allow for identification of renal failure due to obstruction and establish a baseline for future evaluations. Unless febrile or systemically ill, a white blood cell count does not aid in the evaluation

Imaging

It is unclear whether all patients with first time stones require ED imaging for suspected renal colic. For young, healthy patients in whom the diagnosis is clinically clear, one study suggested imaging could be conducted later on an outpatient basis.18 However, another study showed that clinicians are often wrong based on clinical suspicion alone.19 In patients for whom the initial clinical suspicion of stone was 0% to 50%, a stone was present in 29%. In patients for whom the physician had a high pretest clinical suspicion (90% to 100%) of a stone, a stone was present in only 80%. In this same study, CT scanning revealed an alternative diagnosis in 33% of the patients. Thus, these authors strongly advise imaging for patients presenting with a first time stone, with a CT scan to both confirm the suspicion and identify alternative diagnoses.19 As for patients with repeat stones, the issue of imaging hinges on several items. Did the patient have a complication with the previous stone that imaging would aid in preventing? Is the diagnosis in question (i.e., drug seeker, >50)? And finally, for type of evaluation, what is the patient's previous radiation load?

CT In combination, unilateral ureteral dilatation and perinephric stranding have a PPV of 96% for stone disease.21 If both are absent, the NPV is 93% to 97%

US Although useful in the detection of larger stones (Figure 97-3), it may miss smaller (<5 mm in diameter) ureteral stones.27 US is helpful in diagnosing stones in the proximal and distal ureters but is insensitive for mid-ureteral stones. Overall, US has only modest sensitivity and specificity for detecting renal stones (Table 97-3) but is 98% sensitive for detecting hydronephrosis (see Figure 91-2B). However, of hydronephrosis diagnosed by US, up to 22% of studies do not represent obstruction, but rather, normal anatomic variation, full bladder, and renal cysts.24 Rapid bolus infusion of crystalloid can result in a false positive finding of hydroureter.

Pass Rates

Based on stone size alone, 98% of stones <5 mm will pass within 4 weeks without intervention. Sixty percent of stones 5 to 7 mm and 39% of stones >7 mm will pass within 4 weeks. Stone size on plain radiographs is magnified by up to 20%, and a measured stone on CT is 88% of actual stone size

Size

4mm ~75%
4-6mm ~50%
>6mm ~10%

Location in Ureter

Distal ~70%
Middle ~50%
Proximal ~20%

DDx

Cholelithiasis (5%)
Appy (4%)
Pyelonephitis (3%)
Ovarian cyst (2%)
Renal mass (1.4%)
AAA w/or w/o rupture (1.4%)

Differential Diagnoses for Ureterolithiasis

Vascular Aortic dissection Abdominal aortic aneurysm Renal artery embolism Renal vein thrombosis Mesenteric ischemia Renal Pyelonephritis Papillary necrosis Renal cell carcinoma Renal infarct Renal hemorrhage Ureter Blood clot Stricture Tumor (primary or metastatic) Bladder Tumor Varicose vein Cystitis GI Biliary colic Pancreatitis Perforated peptic ulcer disease Appendicitis Inguinal hernia Diverticulitis Cancer Bowel obstruction Gynecologic Ectopic pregnancy Pelvic inflammatory disease/tubo-ovarian abscess Ovarian cyst Ovarian torsion Endometriosis GU Testicular torsion Epididymitis Other Drug-seeking behavior Shingles Retroperitoneal hematoma/abscess/tumor

Treatment

ED
1. Toradol 30mg IV/IM
2. Morphine 3-5mg IV
Outpt
1. NSAIDS PO
2. Vicodin PO
3. Smooth muscle relaxant (alpha-adrenergic blocker)
  1. Tamsulosin (Flomax) 0.4mg PO QHS x 21 days, OR
  2. Terazosin (Hytrin) 1mg PO QHS x 21 days

^IVF of no benefit in acute setting

Surgical Treatment

Persistent obstruction, failure of stone progression, or increasing or unremitting colic Antibiotic penetration into staghorn calculi is poor, and the potential for urosepsis exists as long as the stones remain. Consequently, surgical treatment is recommended for staghorn calculi.

Shock wave lithotripsy, ureteroscopy, or percutaneous nephrolithotomy

Disposition

Admit for:

Intractable pain (on orals)
Solitary or transplanted kidney
Presence of urinary tract infection (UTI), fever, sepsis, or pyonephrosis

Prognosis

Recurrence Rates

1 yr ~33%

5yr ~50%

Increasing H2O intake decreases rate
Protease inhibitors and diuretics increases rate

Source

Tintinalli