Kidney Stones

Question 1

Define the term nephrolithiasis.

Answer 1

Describes the formation of stones within the urinary tract.
80% of stones are composed of calcium (usually oxalate or phosphate). The remainder consist of urate, cystine or struvite (magnesium, ammonium phosphate)

Question 2

Describe the epidemiology of kidney stones.

Answer 2

Common.

Approx 12% people have a renal stone in their lifetime.
Peak incidence between ages of 20 and 50 yrs.
Males more commonly affected 3:1 M:F
—exception of struvite stones, which are associated with UTI’s

Recurrence of stones is common.

Question 3

List some predisposing factors for kidney stones.

Answer 3

Environmental and dietary:
High temperature
Low fluid intake
Low fluid volume
High-protein, high sodium, low calcium diet.

Urine excretion:
High sodium, oxalate or urate
Low citrate

Acquired cases:
Hypercalcaemia of any cause
Ilial disease or resection

Inherited causes:
Cystinuria
Medullary sponge kidney
Renal tubular acidosis type 1

Question 4

Describe the pathogenesis of kidney stones.

Answer 4

Stones develop when urine becomes supersaturated with a stone-forming substance (eg calcium, urate or oxalate).

Crystals develop and aggregate to form stones.

Increased urinary excretion of calcium, urate or oxalate; or reduced excretion of citrate (inhibitor of stone formation) increases the risk of nephrolithiasis.

Stones may remain within the kidney or pass into the ureter and move dismally.

Question 5

Describe the clinical features of kidney stones.

Answer 5

May be asymptomatic, especially if they remain in the kidney.

Stones passing into the ureter Give severe colicky loin pain which often Radiates to the groin.
—Associated with nausea and vomiting.
—Patients typically cannot sit still and require strong analgesia

Stones within the bladder or urethra may cause haematuria, frequency and pain on micturation.

Question 5

What investigations would you order for a patient with suspected kidney stones?

Answer 5

Serum urate and calcium should be measured.

80% stones radioopaque - can be identified with AXR
CT or MRI scans may be needed to identify non-radioopaque stones.
An intravenous pyelogram may identify filling defects within urinary tract.

Urine pH should be measured and urinalysis shows microscopic haematuria.

Unrated stones form in acidic urine whereas alkaline conditions favour formation of struvite stones.

Analysis of a passed stone and measurement of 24hr urinary excretion if calcium, urate, cystine, and oxalate may be useful.

Question 6

How would you manage a patient with kidney stones?

Answer 6

Medical Expulsive Treatment: Suitable for 2 cm or not suitable for other modalities.

Prevention:
•⬆️ Fluid intake (e.g. >3L/day avoiding high Ca2+ water).

• Calcium stones: ⬇️ calcium and vitamin D intake.
• Oxalate stones: ⬇️ oxalate-containing foods and vitamin C intake.
• Uric acid stones: Allopurinol (inhibits xanthine oxidase and uric acid synthesis), urinary alkalization (oral sodium bicarbonate).
• Cystine stones: D-penicillamine, urinary alkalinization.

Question 7

What complications could a patient with urinary stones incur?

Answer 7

Obstruction and hydronephrosis, infection, complications of the cause, e.g. renal failure in primary hyperoxaluria.

Question 8

What prognosis would you expect for a patient with kidney stones?

Answer 8

Approximately 20% of calculi will not pass spontaneously.

Up to 50% of patients may have recurrence within 5 years.