Nephrolithiasis

Question 1

Definition of Nephrolithiasis

Answer 1

When calculic masses crystals, proteins and other substances occur within kidneys

Question 2

Risk Factors of Nephrolithiasis

Answer 2

1. Age
2. Sex
3. Race
4. Geographic Location (Average Temp, Humidity, etc.)
5. Seasonal Factors
6. Fluid Intake
7. Diet
8. Occupation

Question 3

Classification of Urinary Calculi

Answer 3

1. Calcium Stones
   - Types: Calcium Oxalate Stones, Calcium Phosphate Stones
   - Risk Factors: Hypercalciuria, Hyperoxaluria, Hyperuricosuria, Alkaline Urine, Hypoutraturia
2. Struvite Stones
   - Composed of Magnesium-Ammonium Phosphate
   - Associated Conditions: Often linked to UTIs caused by Urease-producing bacteria like Proteus, Klebsiella, or Psuedomonas
   - Characteristics: Can grow large and form ‘Staghorn Stones”, which conform to the shape of Kidney’s internal structure
3. Uric Acid Stones
   - Risk Factors: High Uric Acid Levels in Urine, Acidic Urine (pH <5.0), Gout, High Purine Intake
   - Characteristics: Often Radiolucent (Invisible on plain X-rays)
4. Cystine Stones
   - Associated with Cystinuria and other genetic disorders of amino acid metabolism
   - Characteristics: Form in acidic, caused by an excess of cystine and other amine acids in Urine

Question 4

Pathophysiology of Nephrolithiasis

Answer 4

1. Supersaturation of Salts
   - Stones form when urine becomes supersaturated with salts, meaning there is a higher concentration of salts than urine can dissolve
2. Precipitation
   - Supersaturated salts in Urine Precipitate to form crystals
   - Factors affecting: pH of urine (Alkaline pH favours calcium stone formation, while acidic pH favours uric acid stones), and Temperature (Higher temperature promotes precipitation)
3. Crystallisation
   - Crystals grow from a nucleus (Often a small aggregation of Salts) into Larger stones
   - Key sites: Renal tubules and Papillae (Crystals tent to attach here, and aggregate, forming stones)
   - Matrix: An organic matrix (Proteins, Glycoproteins) in the Kidneys can serve as a structure around which stones grow
4. Inhibitors of Stone Formation
   - Certain substances inhibit Crystal Growth and reduce Stone formation risk: Tamm-Horsfall Protein (Uromodulin), Potassium Citrate, Pyrophosphate and Magnesium

Question 5

Factors increasing Stone Formation Risk

Answer 5

1. Urinary Stasis: Reduced urine flow due to conditions like Benign Prostatic Hyperplasia (BPH)
2. Anatomical Abnormalities: Strictures or Blockages in the Urinary Tract
3. Inflammation: Chronic UTI or Inflammation of the Urinary Epithelium

Question 6

Types of Stones & Specific Associations

Answer 6

1. Calcium Oxalate Stones
   - Often idiopathic; other causes include Increased Calcium Absorption, Decreased Renal Calcium Reabsorption, or Metabolic Conditions like Hyperthyroidism
2. Struvite Stones
   - Alkaline Urine and UTI caused by Urease, producing bacteria are major risk factors; often form large, branching stones known as Staghorn Calculi
3. Uric Acid Stones
   - Linked to high levels of uric acid, frequently seen in patients with gout and those who consume high-purine diets
4. Cystine Stones
   - Rare genetic disorders affecting amino acid metabolism (e.g. Cystinuria), with Cystine precipitating in Acidic Urine

Question 7

Clinical Features of Nephrolithiasis

Answer 7

1. Renal Colic: Intense pain originatingin the flank and radiating to the groin, often due to obstruction of the urinary tract
2. Location specific Pain
   - Pain that radiates to the lateral flank or lower abdomen suggests mid-ureter obstruction
   - Lower UT Symptoms (urgency, Frequent Urination), often indicates obstruction at the lower ureter or ureterovesical junction
3. Additional Symptoms: Nausea, Vomiting, Hematuria (Blood in Urine)

Question 8

Diagnostic Investigations

Answer 8

1. Plain Abdominal X-ray
2. Intravenous Urogram (IVU)
3. Spiral CT Scan
4. Ultrasound

Question 9

Management of Nephrolithiasis

Answer 9

1. Acute Pain Management
   - Strong analgesics like Morphine, Pethidine, or Diclofenac Suppository
2. Increasing Urine Flow
   - Encourage high fluid intake (2L/day) to dilute urine and reduce stone concentration
3. Urinary pH adjustment
   - use of potassium citrate to alkalinise the urine, which can help dissolve certain types of stones
4. Dietary Medications
   - Reduce intake of stone-forming substances (e.g. Oxalate, Sodium, Animal Proteins)
5. Surgical Options
   - Percutaneous Nephrolithotomy: Removal of Large stones via a small incision
   - Ureterscopy: Endoscopic removal of stones from the ureter
   - Lithotripsy (Ultrasonic/Laser): Uses sound waves or laser to break stones into smaller fragments
6. Drug Treatment
   - Medications to dissolve stones have not been successful so far

Question 10

Preventing Recurrence of Stones

Answer 10

1. Hydration
   - Maintain high fluid intake to produce at least 2.5L of urine daily
2. Diet Adjustments
   - Avoid beverages with phosphoric acid
   - Limit oxalate-rich foods
   - Limit animal protein and sodium intake
   - Maintain a balanced calcium intake and increase dietary potassium