Nephrolithiasis

Aetiology

Idiopathic calcium urolithiasis
- Unexplained hypercalciuria with normal serum calcium
- Makes up 70% of patients with stones
Hypercalcaemic disorders
- Primary hyperparathyroidism
- Prolonged immobilisation - bone resorption
- Milk alkali syndrome
  - Ingestion of large quantities of calcium, vitamin D3 and alkali
  - Leads to hypercalcaemia, alkalosis and possible renal impairment
  - Alkalosis compromises renal excretion of calcium
- Sarcoidosis
- Metastatic cancer
- Cushing's disease
- Hyperthyroidism
Renal tubular syndromes
- Renal tubular acidosis - calcium phosphate stones
- Cystinuria - genetic disorder - cystine stones which are radio-opaque
Uric acid lithiasis
- Either excrete excessive amounts of uric acid or have excessively acid urine
- Uric acid remains undissociated and insoluble at pH < 5.5
- Production of uric acid can be increased in myeloproliferative diseases or in those receiving chemotherapy - can cause stones
- Low volume urine can precipitate stones - patients with high-volume ileostomies are at risk
- Mostly faintly radio-opaque
Enzyme disorders
- Primary hyperoxaliuria
- Xanthinuria
- 2, 8 dihydroadeninuria
Secondary urolithiasis
- Secondary hyperoxaliuria - after small bowel resection, or in patients with IBD or chronic pancreatitis with a jejunoileal bypass
- Excess fat in the gut binds with calcium, and low calcium reduces the amount of calcium available to bind oxalate
- Dietary excess - these can increase urinary oxalate
  - Rhubarb
  - Spinach
  - Tea
  - Cocoa
  - Chocolate
  - Pepper
- Infection - some organisms break urea to produce ammonia and CO2. The urine becomes alkaline, promoting formation of struvite calculi (magnesium ammonium phosphate) which can develop into a staghorn calculus.
  - Proteus
  - Pseudomonas
  - Staphylococcus
- Obstruction and stasis - delayed crystal washout
- Medullary sponge kidney - calcium stones
- Urinary diversion - combination of infection, acidosis and stasis
- Drugs - acetazolamide, allopurinol (xanthine stones), thiazide diuretics (uric acid stones)
Others
- Geography
- Climate
- Water intake
- Diet
- Occupation - sedentary jobs in hot environments
- Age - 50% of patients present between 30 and 50
- Slight male preponderance

Presentation

Ureteric colic
May also have 'renal pain'
Dipstick haematuria (visible haematuria is rare)
Dysuria and urgency typically occur once the stone is in the distal ureter

Workup

Initial presentation:
- CT
- X-ray
- Dipstick
  - 95% positive for blood on day 1
  - 65% on day 3
- UEC/FBE
Workup for recurrent stones:
- Indications:
  - Multiple stones
  - Family history stones
  - Other comorbidities such as chronic diarrhoeal states/malabsorption, osteoporosis, UTI, diabetes, gout
  - Medications putting them at higher risk
  - Stones composed of cystine, uric acid, calcium phosphate
  - Dietary habits a/w higher risk of stone formation
- Tests:
  - 24 hours urine - calcium, uric acid, citrate, oxalate, creatinine, pH, sodium, magnesium. Wait a month after stone episode.
  - Bloods - UEC, calcium. Check PTH if calcium high.
  - Urinalysis - look for crystals

Natural history:

90% of stones <5mm in maximal dimension will pass successfully

Management

Indications for inpatient management
- Inability to tolerate PO intake
- Uncontrollable pain
- Fever
Discuss with urology
- Signs of UTI
- AKI
- Anuria
- Unyielding pain, nausea or vomiting
- Stone >10mm (outpatient?)
- Stone does not pass after 4 weeks (outpatient?)
Firm indications for emergency surgery
- Suspected or confirmed infection
- Bilateral obstruction and AKI
- Unilateral obstruction with one functioning kidney
Indications for elective surgery
- Stones >10mm
- Uncomplicated distal ureteric stones <=10mm that have not passed after 4 weeks
- Persistently symptomatic stones
- Pregnant patients in whom observation has failed
- Persistent kidney obstruction
- Recurrent UTI related to stones
Expectant therapy (high likelihood of passing, no sign of infection)
- Analgaesia - paracetamol, NSAID. Opioids if NSAIDs insufficient or AKI.
- Alpha blocker if stone >5 and <=10mm (tamsulosin 0.4mg daily)
- Strain urine

Cystoscopy and JJ stent

Rigid cystoscopy, and locate the ipsilateral UO
Pass a guidewire into the ureter, and advance it using II
- Usually get resistance when you reach the stone - keep gently probing until it passes. Sometimes need to use the ureteric catheter at this point for extra stiffness. If unable to get past, a nephrostomy will be required.
- Advance the wire into the renal pelvis, where it will curl
Pass a 6Fr ureteric catheter over the wire. When it is in the renal pelvis, take the guidewire out, and aspirate some urine for culture through the ureteric catheter. Then switch back to the wire.
Pass a double J stent (26cm for tall patients, 22cm for short, and 24cm for average) up to the pelvis, using a stent pusher over the wire to get it up
Remove the wire completely