Urinary Stone Disease

Essentials of Diagnosis

• Severe flank pain

• Nausea and vomiting

• Identification on noncontrast CT scan or ultrasonography

General Considerations

• Affects 240,000–720,000 Americans per year

• The prevalence of kidney stones has increased to 8.8%, or 1 in 11 Americans, representing a 70% increase over the last 15 years

• Males > females (1.5:1)

• Initial presentation usually occurs in the third through fifth decades; more than 50% of patients will have recurrent stones

• Incidence is greatest during hot summer months

• Contributing factors to urinary stone formation

  • Geographic factors

    • High humidity

    • Elevated temperatures

  • Genetic factors

    • Cystinuria

    • Distal renal tubular acidosis

  • Excess animal protein and salt intake (over 3500 mg daily)

  • Restricted dietary calcium intake

  • Persons in sedentary occupations have a higher incidence than manual laborers

• Increasing evidence is revealing that urinary stone disease may be a precursor to subsequent cardiovascular disease

• Five major types of urinary stones

  • Calcium oxalate

  • Calcium phosphate

  • Struvite (magnesium ammonium phosphate)

  • Uric acid

  • Cystine

• Most urinary stones contain calcium (85%) and are radiopaque; uric acid stones are radiolucent

• Hypercalciuric calcium nephrolithiasis (> 250 mg/24 h) can be caused by absorptive, resorptive, and renal disorders (eTable 23–1)

  • Absorptive hypercalciuria

    • Secondary to increased absorption of calcium at the level of the small bowel, predominantly in the jejunum

    • Can be further subdivided into types I, II, and III

    • Type I: Independent of calcium intake. There is increased urinary calcium on a regular or even a calcium-restricted diet

    • Type II: Dependent on dietary calcium intake

    • Type III: Secondary to a renal phosphate leak, which results in increased vitamin D synthesis and secondarily increased small bowel absorption of calcium

  • Resorptive hypercalciuria

    • Secondary to hyperparathyroidism

    • Hypercalcemia, hypophosphatemia, hypercalciuria, and an elevated serum parathyroid hormone level are found

  • Renal hypercalciuria

    • Occurs when the renal tubules are unable to efficiently reabsorb filtered calcium

    • Hypercalciuria and secondary hyperparathyroidism result

• Hyperuricosuric calcium nephrolithiasis is secondary to dietary excesses or uric acid metabolic defects

• Hyperoxaluric calcium nephrolithiasis is usually due to primary intestinal disorders, including chronic diarrhea, inflammatory bowel disease, or steatorrhea

• Hypocitraturic calcium nephrolithiasis is secondary to disorders associated with metabolic acidosis including chronic diarrhea, type I (distal) renal tubular acidosis, and long-term hydrochlorothiazide treatment

• Uric acid calculi: Contributing factors include

  • Low urinary pH

  • Myeloproliferative disorders

  • Malignancy with increased uric acid production

  • Abrupt and dramatic weight loss

  • Uricosuric medications

• Struvite calculi (magnesium-ammonium-phosphate, "staghorn" calculi)

  • Occur with recurrent urinary tract infections with urease-producing organisms, including Proteus, Pseudomonas, Providencia and, less commonly, Klebsiella, Staphylococcus, and Mycoplasma (but not Escherichia coli)

  • Urine pH ≥ 7.2

• Cystine calculi: Inherited disorder with recurrent stone disease

Symptoms and Signs

• Acute, unremitting, and severe colic

• Typically localized to the flank

• Nausea and vomiting

• Patients constantly moving—in sharp contrast to those with an acute abdomen

• Pain episodic and radiates anteriorly over the abdomen

• With stone in the ureter, pain may be referred into the ipsilateral groin

• With stone at the ureterovesical junction, marked urinary urgency and frequency; in men pain may radiate to the tip of the penis

• After the stone passes into the bladder, there typically is minimal pain with passage through the urethra

• Stone size does not correlate with severity of symptoms

Laboratory Tests

• Serum chemistries and urinalysis should be obtained for all patients with newly diagnosed nephrolithiasis

• Urinalysis

  • Microscopic or gross hematuria (~90%)

  • Absence of microhematuria does not exclude urinary stones

• Urinary pH

  • Persistent urinary pH < 5.5 is suggestive of uric acid

  • Persistent urinary pH > 7.2 is suggestive of a struvite (infection-related) or calcium phosphate stone

Metabolic evaluation

• Stone analysis on recovered stones

• Patients with uncomplicated first-time stones: serum calcium, electrolytes, and uric acid

• For patients with recurrent stones or patients with a family history of stone disease

  • Sodium intake and animal protein intake should be reduced

  • Adequate fluid should be ingested

  • After these changes have been made, obtain 24-h urine collection for urinary volume, pH, calcium, uric acid, oxalate, phosphate, sodium, and citrate excretion

• A serum parathyroid hormone (PTH) level should be checked when hyperparathyroidism is suspected as the cause of calcium oxalate or calcium phosphate stones

• A serum uric acid should be obtained to exclude severe hyperuricemia, which can lead to uric acid stones as well as crystal deposition in the kidneys or heart

Imaging Studies

• Plain film of the abdomen (KUB, kidney-ureter-bladder) and renal ultrasonography will detect most stones

• Noncontrast CT is the most accurate imaging tool for evaluating flank pain given its increased sensitivity and specificity over other tests

• All stones whether radiopaque or radiolucent on KUB are visible on noncontrast CT, except the rare calculi due to indinavir therapy

• However, ultrasound is a safe and effective alternative for initial evaluation of renal colic and can be used in the emergency department with good accuracy

Medications

• Renal hypercalciuria: Thiazides (effective long-term)

• Hyperuricosuric calcium nephrolithiasis

  • Most cases (85%) can be treated with dietary purine restrictions

  • In those cases not reversed with dietary restriction, give allopurinol, 300 mg once daily orally

• Hyperoxaluric calcium nephrolithiasis

  • Adherence to a diet containing moderate calcium intake (1000–1200 mg daily), and avoiding high-oxalate containing foods

  • Low-dose calcium carbonate (250 mg) can be consumed with meals if dietary calcium increases are not successful to reach the 1000 mg daily mark

  • If the diarrhea or steatorrhea cannot be effectively curtailed, oral calcium should be increased with meals, either by ingesting dairy products or taking low-dose calcium carbonate supplements (250 mg)

  • Excess ascorbic acid (> 2000 mg/day) substantially increases urinary oxalate levels

• Hypocitraturic calcium nephrolithiasis

  • Potassium citrate, 40–60 mEq total daily intake, divided either into two or three times daily

  • Oral lemonade

    • Has been shown to modestly increase urinary citrate

    • However, it must be consumed several times every day as oral citrate is cleared from the urine in 6–8 hours

• Uric acid calculi

  • Patients should monitor their urinary alkalinization with Nitrazine pH paper

  • If hyperuricemia is present in addition to hyperuricosuria, give allopurinol, 300 mg once daily orally

• Struvite calculi

  • Relatively soft and amenable to percutaneous removal

  • Appropriate perioperative antibiotics are required

• Cystine calculi

  • Exceptionally challenging to manage medically

  • Prevention is centered around

    • Marked increase in fluid intake during the day and night to achieve a urinary volume of 3–4 L/day

    • Decrease in dietary sodium and cystine intake

    • Urinary alkalinization (typically with high-dose potassium citrate) with a goal urinary pH > 7.0 (monitored with Nitrazine pH paper),

  • Refractory stone formers may be treated with disulfide inhibitors such as tiopronin (alpha-mercaptoproprionylglycine) or penicillamine

  • There are no known inhibitors of cystine calculi

  • Difficult to manage medically

Surgery

• Resorptive hypercalciuria: surgical resection of the parathyroid adenoma

• Infection with ureteral obstruction: a medical emergency requiring both antibiotics and prompt drainage by a ureteral catheter or a percutaneous nephrostomy tube

• Ureteral stones

  • Stones < 5–6 mm in diameter will usually pass spontaneously

  • Active medical expulsive therapy with appropriate pain medications is appropriate for first few weeks

  • Medical expulsive therapy (eg, tamsulosin, 0.4 mg orally once daily, plus ibuprofen, 600 mg orally three times per day on a full stomach, with or without a short course of a low-dose oral corticosteroid [such as prednisone 10 mg orally daily for 5–10 days]) increases rate of spontaneous stone passage

  • Therapeutic intervention is required if spontaneous passage does not occur or if patient has intolerable pain or persistent nausea and vomiting

  • Indications for earlier intervention include

    • Severe pain unresponsive to medications

    • Fever

    • Persistent nausea and vomiting requiring intravenous hydration

  • Distal ureteral stones: ureteroscopic stone extraction or extracorporeal shock wave lithotripsy (SWL)

  • Proximal ureteral stones—those above the superior margin of the sacroiliac joint—as well as intrarenal stones can be treated with SWL or ureteroscopy

• Renal calculi

  • Conservative observation for patients presenting without pain, urinary tract infections, or obstruction

  • Intervention if calculi become symptomatic or grow in size

  • SWL is most effective for stones < 1 cm in the lower pole of the kidney or < 2 cm elsewhere in the kidney

  • SWL is less effective for stones that are very hard (cystine stones, calcium oxalate stones > 1000–1200 Hounsfield units on CT scan) and for obese patients (skin-to-stone distance > 10–12 cm)

  • Ureteroscopy and laser lithotripsy is effective for multiple stones and larger stones, though very large stones may require multiple treatment sessions

  • Stones > 15–20 mm and staghorn stones (large branched stones occupying at least two renal calices) are best treated via percutaneous nephrolithotomy

  • Perioperative antibiotics given as indicated by preoperative urine cultures

Therapeutic Procedures

• Forced intravenous fluid diuresis is not productive and exacerbates pain

Follow-Up

• Routine follow-up every 6–8 months and annual imaging (preferably with ultrasonography)

  • Helps encourage medical compliance

  • Assesses for interval stone formation or growth

  • Permits adjustments in medical therapy based on repeat metabolic studies

Prevention

• To reduce stone recurrences, patients are encouraged to:

  • Increase fluid intake to void 2.5 L/day

  • Ingest fluids during meals, 2 h after each meal, prior to going to sleep in the evening, and during the night

  • Reduce sodium intake

  • Reduce animal protein intake during individual meals

When to Refer

• Evidence of urinary obstruction

• Urinary stone with associated flank pain

• Anatomic abnormalities, solitary kidney, or chronic kidney disease

• Concomitant pyelonephritis or recurrent infection

When to Admit

• Intractable nausea/vomiting or pain

• Obstructing stone with fever or other signs of infection