Kidney stones

Definition

Kidney stones, or renal calculi (nephrolithiasis/urolithiasis), are solid crystalline deposits formed in the urinary tract from supersaturated urine constituents. They can vary in size from microscopic crystals to large staghorn calculi that occupy most of the renal collecting system.

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Epidemiology

• Lifetime prevalence: 10–15% in men, 5–10% in women.

• Peak incidence: Ages 30–50 years.

• Recurrence rate: ~50% within 5–10 years if preventive measures are not taken.

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Types of Kidney Stones

1. Calcium stones (70–80%)

   • Calcium oxalate (most common) or calcium phosphate.

   • Associated with hypercalciuria, hyperoxaluria, hypocitraturia.

2. Uric acid stones (5–10%)

   • Associated with acidic urine (pH <5.5), gout, high purine intake.

3. Struvite stones (10–15%)

   • Magnesium ammonium phosphate.

   • Often related to chronic urinary tract infections by urease-producing bacteria (Proteus, Klebsiella).

   • Can form large staghorn calculi.

4. Cystine stones (<1%)

   • Due to cystinuria, a rare inherited defect in amino acid transport.

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Risk Factors

Metabolic

• Hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia.

• Gout, hyperparathyroidism, obesity, diabetes.

Dietary

• High salt, animal protein, and oxalate intake.

• Low fluid intake.

Anatomical/Functional

• Urinary tract obstruction.

• Medullary sponge kidney.

Infections

• Chronic UTIs (especially for struvite stones).

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Pathophysiology

Kidney stones form when urinary solutes become supersaturated and precipitate into crystals. Nucleation, crystal growth, aggregation, and retention in the urinary tract contribute to stone formation. Urine pH plays a crucial role:

• Acidic urine favors uric acid and cystine stones.

• Alkaline urine favors calcium phosphate and struvite stones.

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Clinical Presentation

Symptoms

• Renal colic: Sudden, severe flank pain radiating to the groin or testicle/labia.

• Hematuria (gross or microscopic).

• Nausea, vomiting.

• Urinary urgency or frequency (stone in distal ureter).

Signs

• Patient often restless, unable to find a comfortable position.

• Costovertebral angle tenderness.

• Possible fever if associated with infection (urgent evaluation required).

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Diagnosis

Laboratory

• Urinalysis: Hematuria, crystals, infection.

• Serum calcium, phosphate, uric acid, creatinine.

• Urine culture if infection suspected.

• 24-hour urine collection for metabolic evaluation in recurrent cases.

Imaging

• Non-contrast helical CT scan: Gold standard for diagnosis and localization.

• Ultrasound: Useful in pregnant patients and detecting hydronephrosis.

• Plain X-ray (KUB): Detects radiopaque stones (calcium-containing).

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Management

1. Acute Stone Episode

Pain control

• NSAIDs (e.g., diclofenac sodium 50–75 mg intramuscularly every 8 hours or ibuprofen 400–600 mg orally every 6–8 hours) unless contraindicated.

• Opioids (e.g., morphine sulfate 2.5–5 mg IV every 4 hours) if pain not controlled.

Hydration

• Encourage oral fluids; IV fluids if unable to drink.

Medical expulsive therapy (for distal ureteric stones 5–10 mm)

• Tamsulosin 0.4 mg orally once daily (alpha-blocker) for up to 4–6 weeks.

Antibiotics

• If infection present, broad-spectrum coverage (e.g., ciprofloxacin 500 mg orally twice daily) adjusted based on culture.

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2. Indications for Urgent Intervention

• Obstructed infected kidney (risk of sepsis).

• Uncontrolled pain or vomiting.

• Anuria or acute kidney injury.

• Bilateral obstruction or solitary kidney obstruction.

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3. Definitive Stone Removal

• Extracorporeal Shock Wave Lithotripsy (ESWL): For stones ≤20 mm in kidney or upper ureter.

• Ureteroscopy with laser lithotripsy: For ureteral stones or ESWL failure.

• Percutaneous Nephrolithotomy (PCNL): For large (>20 mm) or complex stones.

• Open or laparoscopic surgery: Rarely used.

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4. Prevention of Recurrence

General measures

• Increase fluid intake to maintain urine output ≥2–2.5 L/day.

• Balanced diet with normal calcium, reduced salt and animal protein.

Specific measures (based on stone type)

• Calcium oxalate: Thiazide diuretics (e.g., hydrochlorothiazide 25 mg orally once daily).

• Uric acid: Allopurinol 100–300 mg orally daily; alkalinize urine with potassium citrate 20–40 mEq/day in divided doses.

• Struvite: Eradicate infection; may require surgical removal.

• Cystine: High fluid intake, urinary alkalinization, and in some cases tiopronin 800–1,200 mg/day orally in divided doses.

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Complications

• Hydronephrosis and renal impairment.

• Urinary tract infections and sepsis.

• Chronic kidney disease (rare in well-managed cases).

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Prognosis

• Good with prompt treatment.

• High recurrence risk; requires long-term preventive strategies.