Renal Stone Disease

Background/Epidemiology

• Common (prevalence ~1.2%; lifetime risk around 7%)
• There is a strong risk of recurrence (50% at 5-7 years)

Classification

• Size
  • <5; 5-10; 10-20; >20 mm
    • Most under 5mm will pass spontaneously
• Location
  • Upper, middle or lower calyx (within the kidney)
  • Renal Pelvis
  • Upper, middle, distal third of ureter
  • Bladder/Urethra
• X-ray characteristics
  • Radiopaque e.g. Calcium oxalate; calcium phosphate (both most common)
  • Poor radiopacity e.g. magnesium ammonium phosphate (struvite); apatite; cystine
  • Radioluscent e.g. urate; ammonium urate; xanthine; drug stones
• Aetiology
  • Non-infectious stones – most commonly a metabolic defect (predisposing factors include low urine volume/fluid intake; high protein and salt diet; high sodium/oxalate/urate excretions or low citrate excretion; hypercalcaemia; ileal disease/resection; renal tubular acidosis)
    • Calcium oxalate and phosphate stones; urate stones
  • Infections
    • struvite
  • Genetic causes (e.g. familial hypercalciuria; medullary sponge kidney; cystinuria; renal tubular acidosis type I; primary hyperoxaluria)
  • Other predisposing factors include hyperparathyroidism

Clinical Features

• Majority are asymptomatic (incidental stone disease).  Around one third will develop symptoms
• Classic acute loin to groin colicky pain associated with nausea and vomiting
  • + renal angle tenderness and microscopic haematuria (gross haematuria may also be seen)
  • Fever/chills are not classical of stone disease but may be seen if there is associated infection
  • there may also be symptoms of urinary tract infection i.e. frequency, dysuria
• Pain is often restless, patients often seen writhing in distress

Investigations

• While most stones (calcium containing) can often be visualised on AXR, gold standard is CTKUB (NCCT); however, in Tayside, the investigation of choice is CT-stone search
  • IVU is not routinely used for investigating flank pain
• Other investigations include
  • urinalysis + culture (consider infection)
  • Serum U&Es (calcium, phosphate; bicarbonate; urate; eGFR/creatinine)
    • PTH levels (if raised calcium)
  • Also FBC and CRP (infection)
• If a stone has been passed, stone analysis
• With recurrent stones, urine studies (urea, electrolytes etc) should be performed also

Management

• Pain management
  • NSAID 1st line (diclofenac) and opiates 2nd line (oromorph or IM morphine)
• Stone relief
  • If stone <10mm and there are no indications for active removal, observation and periodic evaluation is possible (European guidelines also suggest medical expulsion therapy- α-blocker e.g. tamsulosin; particularly for stones 5-10mm)
    • Indications for active removal include
      • stones unlikely to pass spontaneously (>15mm); obstruction caused by stones; renal dysfunction; persistent pain despite analgesia; comorbidity (especially patients with a solitary kidney)
  • The choice of procedure for active removal depends on stone size and location
    • Kidney
      • >20mm- Percutaneous nephrolithotomy (1st line unless contraindicated); Retrograde intrarenal surgery (or Flexible uretorenoscopy) or Electrocorporeal Shock Wave Lithotripsy (ESWL) (second line; choice depends on whether stone is susceptible to ESWL)
        • Contraindications to PNL include
          • untreated UTI; tumour in the area or potential malignant kidney tumour; pregnancy
        • Factors making ESWL less likely include
          • Shockwave-resistant stones e.g. calcium oxalate monohydrate, brushite or cystine; Steep infundibular pelvic angle; long lower pole calyx; narrow infundibulum (<5mm)
      • 10-20mm- ESWL or Endourology (PNL/URS) (depends again on influencing factors)
      • <10mm- ESWL 1st line (or URS if unsuitable); PNL 2nd line
  • NB If there are complications
    • If there’s hydronephrosis, urgent decompression with percutaneous nephrostomy
• Prevention of recurrence/metabolic management
  • Fluids/General
    • Aim for urine output >2.5l in 24 hours
    • Restrict salt intake
    • Avoid excessive animal protein
  • For calcium stones
    • Normocalciuria
      • Oral potassium citrate (increases urine pH and citrate excretion)
    • Hypercalciuria
      • Thiazide diuretics (often with potassium citrate)
        • If magnesium loss is a concern (chronic diuretic use), consider potassium magnesium citrate
    • Hyperuricaemia/Hyperuricosuria
      • Allopurinol and potassium citrate
    • Hyperoxaluria
      • If >1mmol/day- pyridoxine (start low-dose)
      • If >0.5mmol/day- calcium supplementation (250-1000mg QDS- beware rise in calcium)
  • For struvite stone- treat infection; prevention may include acetohydroxamic acid (AHA) although side effects are troublesome
  • Cystine stones- potassium citrate and other cystine binders e.g. D-penicillamine/ tiopronin