Urinary Stone Disease

KEY FEATURES

Essentials of Diagnosis

• Severe flank pain

• Nausea and vomiting

• Identification of urinary stone on noncontrast CT scan or ultrasonography

General Considerations

• 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 on plain abdominal radiographs

• Uric acid stones may be radiolucent if pure, or partially radiopaque if mixed with calcium

• Cystine and struvite stones are faintly radiopaque

• 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

  • Many commonly prescribed medications

    • Carbonic anhydrase inhibitors (topiramate, zonisamide, acetazolamide)

    • Systemic corticosteroids (prednisone)

    • Antiretroviral protease inhibitors (indinavir and others)

    • Gout medications (probenecid)

    • Diuretics (furosemide, bumetanide, torsemide, triamterene)

    • Decongestants (guaifenesin, ephedrine)

    • Laxatives (if abused for weight loss)

  • Dietary and other factors

    • Sedentary lifestyle

    • Obesity

    • Hypertension

    • Insulin resistance and poor glycemic control

    • Carotid calcification

    • Cardiovascular disease

    • High protein and salt intake

    • Inadequate hydration

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

• Hypercalciuric calcium nephrolithiasis (> 250 mg/24 h) can be caused by absorptive, resorptive, and renal disorders (eTable 25–1)

  • Absorptive hypercalciuria

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

    • Can be diet-dependent, independent of calcium intake, or due to renal phosphate leak

  • Resorptive hypercalciuria

    • Primary hyperparathyroidism

    • Typically due to a parathyroid adenoma

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

  • Renal hypercalciuria

    • Most common form of hypercalciuria

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

    • Spilling calcium in the urine may result in secondary hyperparathyroidism with normal serum calcium

• Hyperuricosuric calcium nephrolithiasis is secondary to dietary purine excess 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