Renal calculi, nephrocalcinosis, and urinary tract obstruction

Question 1

What types are renal stones can occur?

Answer 1

Calcium oxalate +/- calcium phosphate (65%)
-commoner in men
Calcium phosphate alone (15%)
Struvite (10-15%)
Uric acid (3-5%)
Cystine (1-2%)

Question 2

What is the lifetime risk of renal stones?

Answer 2

10%

Commoner in men (2:1)

Question 3

What is the likelihood of recurrence with renal stone disease? Name 2 factors that increase the likelihood

Answer 3

50% experience a second stone within 10 years

Metabolic or structural abnormalities predisposing to stone formation, that are not modified by treatment

Question 4

Name 5 risk factors/causes for urinary tract stones

Answer 4

Dehydration
Hypercalcaemia: primary hyperthyroidism, vitamin D, sarcoidosis
Hypercalciuria: hypercalcaemia, high calcium intake, immobilisation, idiopathic
Hyperoxaluria
Hyperuricaemia and hypouricosuria
Urinary tract infection
Cystinuria
Primary renal disease: polycystic kidneys, medullary sponge kidneys, renal tubular acidosis
Drugs:
Calcium stones: loop diuretics, glucocorticoids, theophylline, vitamin D and C
Uric stones: thiazide diuretics, salicylates

Question 5

Describe the clinical features of urinary tract stones

Answer 5

Majority are asymptomatic

Pain*: sharp or dull, constant, intermittent, or colicky
Fluids or diuretics may worsen pain if obstructed
Exertion may precipitate pain and haematuria
Ureteric colic:
-radiate from flank to iliac fossa
-pallor, sweating, vomiting
-restless, unable to sit still

Urinary tract infection and/or obstruction

Question 6

Describe the clinical features of bladder stone

Answer 6

Usually associated with bacteriuria

Frequency, dysuria, haematuria
Trigonitis: severe perineal pain

Obstruction: anuria and painful bladder distension

Question 7

How should suspected urinary tract stones be investigated?

Answer 7

Urinalysis: RBCs, protein, glucose
Chemical analysis of any passed stone
Mid-stream urine sample: microscopy and culture

U&Es, creatinine (eGFR), calcium

USS: 45% sensitivity, 90% specificity
-can quickly identify complications e.g. hydronephrosis
Non-contrast CT-KUB: >95% sensitivity

Question 8

Outline the management of urinary tract stones

Answer 8

Diclofenac for renal colic
Alpha-blockers (e.g. tamsulosin): aids passage of stones

<5mm: usually pass spontaneously
<2cm: shock wave lithotripsy
<2cm + pregnant: ureterscopy
Complex or staghorn calculi: percutaneous nephrolithotomy

Ureteric obstruction + infection ➔ emergency
-decompression: nephrostomy tube, ureteric catheter, or ureteric stent

Question 9

Describe the prognosis of renal stones

Answer 9

<5mm: usually pass spontaneously within 4 weeks

>1cm: usually need urological or radiological intervention

Question 10

How can recurrent renal stones be prevented?

Answer 10

Calcium stones:
High fluid intake to ensure 2-2.5L/d of urine
Low animal protein and low salt diet
Thiazide diuretics

Avoid foods rich in oxalate: nuts, spinach, chocolate

Uric acid stones: allopurinol and oral bicarbonate