Nephrolithiasis: clinical approach

Nephrolithiasis, also referred to as renal calculi or kidney stones, is a condition characterized by the painful formation of crystals in the kidneys, which may lead to obstructions in the urinary tract. This condition typically arises when there is an excess saturation of minerals and salts in the urine, such as calcium, oxalate, and uric acid. The main types of kidney stones are calcium oxalate, calcium phosphate, uric acid, cystine, and struvite stones.

When a patient presents with symptoms indicative of nephrolithiasis, begin with an ABCDE assessment to evaluate whether the patient is stable or unstable. In cases of instability, prioritize securing the airway, breathing, and circulation, establish IV access, and initiate continuous monitoring of vital signs such as blood pressure, heart rate, and pulse oximetry. Administer supplemental oxygen as necessary.

It's crucial to recognize that nephrolithiasis accompanied by a urinary tract infection constitutes a medical emergency requiring prompt decompression and drainage to prevent severe complications like pyelonephritis, renal abscess, or sepsis. It’s also considered an emergency in scenarios such as renal failure, anuria, bilateral ureteral obstruction, or a solitary functioning kidney, which necessitates immediate consultation with a urology specialist.

For stable patients, after completing the ABCDE assessment, proceed with a detailed history and physical examination, and order urinalysis. Common symptoms of nephrolithiasis include sudden, severe flank pain, hematuria, dysuria, nausea, or vomiting. Physical exams typically show unilateral flank tenderness. Urinalysis may reveal the presence of red and white blood cells, along with urinary crystals.

If these symptoms and test results suggest nephrolithiasis, proceed with a non-contrast helical CT scan of the abdomen and pelvis to confirm the presence of stones. Should the CT scan be negative, then alternative diagnoses should be considered. If the scan identifies a stone, the diagnosis of nephrolithiasis is confirmed.

For imaging, a helical CT scan is the preferred method as it can detect both radiolucent and radiopaque stones as small as 1 mm and identify hydronephrosis. In contrast, X-rays are limited to detecting larger radiopaque stones, and while ultrasound can detect hydronephrosis, it generally does not reliably identify stones beyond the proximal ureter.

Following diagnosis, the initial management should focus on pain relief, preferably with an intravenous NSAID like ketorolac. NSAIDs are favored over opioids, which should only be used if NSAIDs are contraindicated, if kidney function is severely impaired, or if pain remains uncontrolled by NSAIDs.

Subsequent steps involve reviewing the CT scan to determine the stone's size, which will guide further treatment. Stones 6 millimeters or larger are unlikely to pass spontaneously and may require intervention by a urologist, such as extracorporeal shock wave lithotripsy or endoscopic removal. Conversely, stones smaller than 6 millimeters might pass naturally. In such cases, monitor the patient for spontaneous stone passage over 4 weeks, advise them to use a calculi strainer to catch any passed stones, and consider prescribing alpha-blockers like tamsulosin to facilitate the passage by relaxing the ureteral smooth muscle.

Next, evaluate whether the stone has been expelled after a 4-week observation period. If the stone remains unpassed or if the patient's symptoms persist, consider seeking a urological consultation to explore options like extracorporeal shock wave lithotripsy or endoscopic stone removal. Additionally, patients with persisting renal stones face an increased risk of developing hydronephrosis. It is essential to monitor these patients bi-weekly with renal ultrasounds to check for any signs of hydronephrosis or blockage in the proximal ureter. Conversely, if the stone has passed naturally, no further specialist consultations are necessary.

Regardless of whether the stone is surgically removed or passes naturally, it's crucial to analyze the stone type to tailor prevention strategies effectively. This involves conducting a series of tests, including a 24-hour urine collection to measure urinary pH and levels of calcium, oxalate, citrate, uric acid, and phosphorus. You should also request urine microscopy and a renal stone composition analysis.

For instance, if the 24-hour urine analysis shows elevated levels of calcium and oxalate, reduced citrate levels; and the stone composition and urine microscopy identify envelope or dumbbell-shaped crystals typical of calcium oxalate stones, the treatment protocol should include thiazide diuretics to reduce calcium excretion, potassium citrate to alkalinize the urine, and dietary adjustments to lower intake of sodium, oxalate, and non-dairy animal proteins.

If the 24-hour urine results indicate high levels of calcium and phosphate, low citrate, and a pH of 6.5 or higher, and if urine microscopy reveals amorphous wedge-shaped crystals in a rosette pattern, this suggests calcium phosphate stones. The management of these stones involves thiazide diuretics to decrease urine calcium and a low-sodium diet.

A key clinical point is to measure serum calcium to screen for hyperparathyroidism, which is often linked to calcium phosphate stones. Elevated serum calcium levels should prompt further testing for parathyroid hormone levels to assess for primary hyperparathyroidism and 25-hydroxy vitamin D to check for secondary hyperparathyroidism caused by a vitamin D deficiency.

If laboratory findings indicate a urine pH of 5.5 or lower and urine microscopy shows rhomboid-shaped crystals, this suggests uric acid stones. The primary treatment includes alkalinizing the urine with potassium citrate and a diet low in non-dairy animal proteins. If these measures are insufficient, consider administering a xanthine oxidase inhibitor like allopurinol to reduce serum uric acid levels. It's also advisable to address any underlying conditions such as diabetes, obesity, and gout, which are commonly associated with uric acid stones.

For cystine stones, indicated by hexagon-shaped crystals and confirmed through stone composition analysis, the recommended preventative measures include urine alkalinization using potassium citrate and dietary modifications to reduce sodium and non-dairy animal protein intake. If these initial steps are ineffective, consider treatment with chelating agents like penicillamine to bind cystine.

In cases of a urine pH exceeding 8 and urine microscopy showing coffin lid-shaped crystals, diagnose struvite stones, also known as magnesium ammonium phosphate stones. These stones are often associated with urinary infections from urease-producing bacteria. Addressing any concurrent infections and taking preventative measures against future urinary infections are crucial for managing struvite stones, which can grow large and form a staghorn shape, often necessitating surgical intervention.

Lastly, regardless of the stone type, promoting adequate fluid intake is critical for preventing future stone formation. Encourage patients to maintain sufficient hydration to produce at least 2.5 liters of urine daily. This practice helps dilute urine and reduces the risk of new stone formation.

To summarize:

1. **Initial Evaluation**: Once nephrolithiasis is suspected based on symptoms, proceed with a non-contrast helical CT scan of the abdomen and pelvis to identify any stones.

2. **Diagnosis and Initial Management**: If the CT scan shows a stone, confirm the diagnosis of nephrolithiasis. Begin pain management, ideally with intravenous NSAIDs, which are effective and have fewer side effects compared to opioids.

3. **Assessment of Stone Size**: Determine the size of the stone:

- **Stones ≥ 6 mm**: These are unlikely to pass spontaneously. Consult the urology or surgical team to discuss interventions like extracorporeal shock wave lithotripsy or endoscopic removal.

- **Stones < 6 mm**: These may pass naturally. Monitor the patient for spontaneous passage over a 4-week period.

4. **Follow-Up**: If the stone does not pass or symptoms persist:

- **Reconsultation**: Get back in touch with the urology team for potential intervention.

5. **Post-Passage or Removal Analysis**:

- Regardless of whether the stone passes on its own or is surgically removed, conduct further urine studies to analyze stone composition. This helps in identifying the type of stone (e.g., calcium oxalate, calcium phosphate, uric acid, cystine, struvite), which is essential for tailoring preventive measures and treatment for recurrence.

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作者：Joy，

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