Urolithiasis

Question 1

AETIOLOGY: Stones

Answer 1

Primary

• dehydration
• hypercalciuria, hyperparathyroidism, hypercalcaemia
• cystinuria
• high dietary oxalate
• renal tubular acidosis
• medullary sponge kidney, polycystic kidney disease
• beryllium or cadmium exposure

Risk factors for urate stones

• gout
• ileostomy: loss of bicarbonate and fluid results in acidic urine, causing the precipitation of uric acid
• Drug causes*
• loop diuretics, steroids, acetazolamide, theophylline

Question 2

CLASSIFICATION: Stones

Answer 2

1. Calcium oxalate - 85%

• Hypercalciuria is a major risk factor
• Hyperoxaluria may also increase risk
• Hypocitraturia increases risk because citrate forms complexes with calcium making it more soluble
• Stones are radio-opaque
• Hyperuricosuria may cause uric acid stones to which calcium oxalate binds

2. Cystine - 1%

• Inherited recessive disorder of transmembrane cystine transport leading to decreased absorption of cystine from intestine and renal tubule
• Multiple stones may form
• Relatively radiodense

3. Uric acid - 5-10%

• Uric acid is a product of purine metabolism
• May precipitate when urinary pH low
• May be caused by diseases with extensive tissue breakdown e.g. malignancy
• More common in children with inborn errors of metabolism
• Radiolucent

4. Calcium phosphate - 10%

• May occur in renal tubular acidosis, high urinary pH increases supersaturation of urine with calcium and phosphate
• Renal tubular acidosis types 1 and 3 increase risk of stone formation (types 2 and 4 do not)
• Radio-opaque stones (composition similar to bone

5. Struvite Stones - 2-20%

• magnesium, ammonium and phosphate
• Occur as a result of urease producing bacteria (and are thus associated with chronic infections)
• Slightly radio-opaque

Question 3

CLINCIAL FEATURES: STONES

Answer 3

1. Renal colic

• Acute, severe flank pain
• Writhing with pain, not alleviated by position
• Radiates to ipsilateral groin

2. Nausea and vomiting

3. Urinary frequency/urgency

4. Non-visible haematuria

• Stones cause microtrauma
• Rarely macroscopic

5. Testicular pain

• As stones pass through ureter, flank pain can radiate towards groin and testicle

6. History/Other

• Obesity
• Family history
• PHx Stones (50% have recurrence within 10 yrs)

Question 4

INVESTIGATIONS: Stones

Answer 4

• Culture*
• Urinalysis - 97% microscopic haematuria
• Bloods*
• FBC, U&Es (Ca²⁺, PO₄^3-, urate)
• Imaging*
• CT KUB*
• Common sites of obstruction: pelvic-ureteric junction, pelvic brim, vesico-ureteric junction (VUJ)

Question 5

MANAGEMENT: Stones

Answer 5

Conservative

• Analgesisa (NSAIDs)
• Fluids/anti-emetics
• Most stones <6mm pass spontaneously

Medical

• Alpha blockers (e.g. TAMSULOSIN) +/- corticosteroids
• Calcium channel bockers (Nifidipine)

Surgical

• Extracorpeal shockwave lithotripsy (small <2cm)
• Urinary stent (larger stones/complete obstruction)
• Percutaneus nephrolithotomy (>2cm)
• Emergency percutaneous nephrostomy (septic & obstructed)

Question 6

What is NICE management strategy for renal colic?

Answer 6

IM DICLOFENAC 75mg