Nephrolithiasis¶
Chapter 330 | Part 9: Disorders of the Kidney and Urinary Tract
KEY CLINICAL POINTS¶
- Nephrolithiasis is a global condition with ~10-20% lifetime prevalence, higher in white men (3.5 cases/1000 at age 40) and lower in Black individuals (~50% less).
- Calcium oxalate stones (~75%) are most common, followed by calcium phosphate (~15%), uric acid (~8%), and struvite (~1%).
- Dietary factors (high animal protein, sodium, oxalate, sucrose) and urinary risk factors (low fluid intake, low citrate) are key contributors to stone formation.
- Prevention focuses on increasing urine volume (>2 L/day), dietary modifications (calcium, potassium, magnesium), and targeted pharmacotherapy (thiazides, citrate).
- Noncontrast helical CT is the gold standard for diagnosis, with 24-hour urine analysis guiding individualized management.
1. DEFINITION & OVERVIEW¶
Nephrolithiasis (kidney stone disease) is a common, painful, and costly condition characterized by the formation of solid crystalline deposits in the urinary tract. Stones can cause renal colic, hematuria, and obstructive complications. Recurrence rates are high (~50% within 10 years), emphasizing the importance of preventive strategies.
Stone Composition and Prevalence¶
| Stone Type | Prevalence (%) | Key Features |
|---|---|---|
| Calcium Oxalate | 75 | Most common; insensitive to urine pH |
| Calcium Phosphate | 15 | More common at urine pH ‡6.5 |
| Uric Acid | 8 | Formed at urine pH £5.5 |
| Struvite | 1 | Associated with UTIs |
| Cystine | <1 | Genetic disorder (cystinuria) |
Dietary Risk Factors for Stone Formation¶
| Dietary Component | Risk Association | Mechanism |
|---|---|---|
| Animal Protein | Increased | Raises calcium and uric acid excretion |
| Oxalate | Increased | Promotes calcium oxalate stones |
| Sodium | Increased | Increases calcium excretion |
| Dietary Component | Risk Association | Mechanism |
|---|---|---|
| Sucrose/Fructose | Increased | Promotes uric acid and calcium oxalate stones |
| Calcium | Neutral/Protective | Reduces oxalate absorption |
1.1 Stone Composition and Types¶
Common stone types include calcium oxalate (~75%), calcium phosphate (~15%), uric acid (~8%), struvite (~1%), and cystine (<1%). Mixed stones and drug-induced stones (e.g., acyclovir, triamterene) are also possible. Stone type guides prognosis and prevention strategies.
1.2 Pathophysiology¶
Stone formation involves supersaturation of urine with lithogenic salts (calcium, oxalate, uric acid) and reduced inhibitors (citrate). Dietary and metabolic factors, along with urinary pH, influence crystal nucleation and growth.
2. EPIDEMIOLOGY¶
Nephrolithiasis is a global disease with increasing prevalence due to Westernized lifestyles. Lifetime risk is ~20% in men and 10% in women. Prevalence is ~50% lower in Black individuals than in whites. Annual incidence peaks in white men at 3.5 cases/1000 at age 40, declining to 2 cases/1000 by age 70. Recurrence rates are high (~50% within 10 years).
2.1 Demographics¶
Highest incidence in middle-aged white men; stones can occur in infants and elderly. Geographic variability exists, with highest prevalence in the southeastern U.S. Obesity and weight gain are significant risk factors.
2.2 Risk Factors¶
Dietary (high animal protein, sodium, oxalate), urinary (low fluid intake), and nondietary (age, race, body size) factors contribute. Genetic predisposition (family history) increases risk by >2-fold.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Stone formation involves supersaturation of urine with lithogenic salts and reduced inhibitors. Dietary and metabolic factors, along with urinary pH, influence crystal nucleation and growth. Genetic disorders (e.g., primary hyperoxaluria, cystinuria) and metabolic conditions (e.g., hyperparathyroidism) contribute to specific stone types.
3.1 Supersaturation and Inhibitors¶
Urine supersaturation with calcium, oxalate, or uric acid promotes crystal formation. Citrate, magnesium, and potassium inhibit crystallization. Supersaturation is a continuous variable, not a binary threshold.
3.2 Genetic Disorders¶
Primary hyperoxaluria (autosomal recessive) causes excessive oxalate production. Cystinuria (autosomal recessive) leads to cystine stone formation. Genome-wide studies identify common genetic contributors.
4. CLINICAL FEATURES¶
Acute presentations include renal colic (sudden, severe flank pain radiating to groin) and painless gross hematuria. Complications include obstructive uropathy, UTIs, and renal failure. Chronic presentations may involve recurrent stones, hypertension, and metabolic disorders.
4.1 Symptomatology¶
Renal colic: unilateral flank pain, nausea, vomiting. Painless hematuria: visible blood in urine without pain. Obstructive complications: pyelonephritis, hydronephrosis, and sepsis.
4.2 Complications¶
Chronic kidney disease, renal failure, and recurrent UTIs. Stones in the ureter may mimic appendicitis (right side) or diverticulitis (left side).
5. DIFFERENTIAL DIAGNOSIS¶
Acute renal colic must be differentiated from appendicitis, diverticulitis, ovarian torsion, and ureteral tumors. Painless hematuria may mimic bladder cancer or glomerulonephritis. Obstructive UTIs require urgent intervention.
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnosis combines history, physical exam, and imaging. Noncontrast helical CT is the gold standard for detecting stones. 24-hour urine analysis measures supersaturation and guides prevention. Urinalysis reveals red/white blood cells and crystals.
6.1 Imaging¶
Noncontrast CT (gold standard) detects stones as small as 1 mm. Ultrasound is used for radiation avoidance but less sensitive. KUB radiography may miss ureteral stones.
6.2 Laboratory Tests¶
Serum electrolytes, calcium, uric acid, and PTH. Urinalysis shows crystals, hematuria, and infection markers. 24-hour urine collection measures calcium, oxalate, citrate, and pH.
7. MANAGEMENT & TREATMENT¶
Acute management includes analgesia (NSAIDs preferred over opioids), hydration, and ureteral stenting. Long-term prevention focuses on increasing urine volume, dietary modifications, and pharmacotherapy (thiazides, citrate). Surgical interventions (ESWL, ureteroscopy) are used for large stones.
7.1 Acute Pain Management¶
NSAIDs (e.g., ketorolac) are as effective as opioids with fewer side effects. Hydration (2 L/day) and alpha-blockers (tamsulosin) improve stone passage.
7.2 Preventive Strategies¶
Dietary changes (low sodium, moderate calcium, high fluid intake), thiazide diuretics for hypercalciuria, and potassium citrate for hypocitruria. Bisphosphonates may be used for osteoporosis but not solely for stones.
8. PROGNOSIS & COMPLICATIONS¶
Recurrence rates are high (~50% within 10 years), emphasizing the need for prevention. Complications include chronic kidney disease, renal failure, and sepsis from obstructive UTIs. Long-term follow-up is essential for patients with recurrent stones.
8.1 Recurrence Prevention¶
Lifestyle modifications (fluid intake, diet) and targeted pharmacotherapy reduce recurrence by ~50% in calcium oxalate stones. Genetic counseling is important for hereditary disorders.
8.2 Long-Term Risks¶
Chronic kidney disease, metabolic bone disease, and increased cardiovascular risk. Patients with recurrent stones require regular monitoring and tailored interventions.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Avoid NSAIDs; use hydration and conservative management. Pediatrics: Stones may be asymptomatic; imaging must minimize radiation. Elderly: Consider comorbidities and renal function. Obesity: Address metabolic syndrome and dietary factors.
9.1 Pregnancy¶
Avoid NSAIDs; use hydration and conservative management. Stones may be asymptomatic in infants; imaging should avoid radiation.
9.2 Elderly Patients¶
Consider renal function, comorbidities, and medication interactions. Hydration and dietary modifications are critical for prevention.
10. KEY POINTS & CLINICAL PEARLS¶
- Increase urine volume to >2 L/day to prevent stone formation. 2. Dietary calcium reduces oxalate absorption; avoid high-dose vitamin C. 3. Thiazides and potassium citrate are first-line for hypercalciuria. 4. Noncontrast CT is the gold standard for diagnosis. 5. Recurrence rates are high; lifelong prevention is essential.