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Approach to Renal Stones College of Medicine Physician Course 2013
Outline
• Epidemiology • Presentation and Pathogenesis • Contributing factors • Evaluation • Management strategies • Summary
Epidemiology • USA (NHANES data 2007-2010)
Scales et al. European Urology 2012
Incidence and Prevalence • Annual incidence 0.6-1.5%
• Prevalence 2-7%
• Lifetime risk 10-20%
• Male>Female
• Caucasians>Hispanics and Asians>African Americans
• No data available for Asia
Clinical presentation • Asymptomatic • Abdominal pain • Haematuria • Urinary tract infection • CKD/ESRD
Stone types
Pathogenesis
• Supersaturation • Imbalance of modifiers • Epithelial factors
Supersaturation
• Ratio urinary Calcium Oxalate or Calcium Phosphate concentration: solubility
• At levels <1 crystals dissolve • At levels >1 crystals can nucleate and grow
Imbalance of modifiers • Anatomical factors
o Urinary stasis - caused by ureteropelvic junction obstruction, horseshoe kidney or polycystic kidneys
• Hypercalciuria o Usually familial or idiopathic o Would a low Ca diet help?
• Calcium binds oxalate in the gut hindering its absorption therefore low Ca diet may actually result in increased Ca Oxalate stone formation!
• Hypocitraturia - increases risk of stone formation o can occur in distal RTA, hypokalaemia, carbonic anhydrase
inhibitor use (topiratmate) • Hyperuricosuria
o due to increased purine intake o promotes calcium stones by decreasing Ca Oxalate solubility
Epithelial factors
• Stones can form over regions of interstitial CaPhosphate deposits on the papillary surface (Randall’s plaques); usually in idiopathic CaOxalate recurrent stone formers
• Idiopathic CaPhosphate stones tend to form over the inner medullary collecting ducts that contain apatite or other crystals
Contributing factors • Obesity • Lower
socioeconomomic status
• Metabolic syndrome
Scales et al. European Urology 2012
Associated Factors (Ca stones)
Worcester, Coe. NEJM 2010
Worcester, Coe. NEJM 2010
Causes of renal calculi
Calcium stones Primary Hyperparathyroidism Medullary sponge kidney Distal renal tubular acidosis Uric acid stones Acidic urine (pH<5.5) UA overproduction and secretion
Struvite stones Urease-producing organisms (proteus/klebsiella) Cystine stones Cystinuria (AR disorder)
Evaluation • Comprehensive evaluation indicated for
o Multiple/recurrent stones
o Progressive calculi (increasing in size or number)
o Children, Non-caucasians
o Non calcium containing calculi
o Solitary kidney
o (Metabolic syndrome)
To Evaluate or not? • Doing something
o Uncover underlying condition e.g. primary hyperparathyroidism o Associated conditions e.g. low bone density o Tailor therapy o Follow efficacy of therapy
• Doing nothing o Recurrence rate 50-60% in 10yrs; 70-80% in 20 yrs o Empirical Rx can be effective
• Increase fluid intake • Decrease salt and protein in the diet • Alkali Rx
Imaging
Plain Xray
US
CT KUB
IVU MRI
Two separate 24 hour urine collection, while on usual diet and activities for: Urine Vol pH Calcium Oxalate Uric acid Citrate Sodium Creatinine
Treatment options for renal calculi
Symptoms
Conservative Surgical
Yes No
<7mm >7mm
Percutaneous nephrolithotomy Shock wave lithotripsy
Ureteroscopy Open/Laparoscopic surgery
Annual Imaging
Stones <5mm more likely to pass (p=0.006)
20% incidence of spontaneous passage
Only 7.1% required intervention eventually
Ureteric obstruction Koh LT et al. BJUI 2011
Chandrashekar K et al. AJM 2012
Recurrence prevention
• Fluid intake
• Dietary restrictions? o Low animal protein, Na, oxalate with normal Ca intake vs low Ca and
oxalate intake 36,37
o Low sodium diet can decrease excretion of both calcium and oxalate
• Thiazides
• Potassium citrate
Clinical trials in pharmacotherapy
Sakhaee et al.J Clin Endocrinol Metab, June 2012
Preventative measures
Worcester, Coe. NEJM 2010
Fluid intake
• Ensuring a urine volume of >2L/day was associated with reduced urinary supersaturation of CaOxalate and reduced stone recurrence
Borghi et al. J Urol 1996
Dietary contributory factors
• High animal protein diet • High salt diet • High oxalate containing foods • Low calcium diet • Excessive Vit C and D • Excessive fructose intake
Dietary interventions • Low calcium diet? • In men with recurrent
calcium oxalate stones and hypercalciuria, restricted intake of animal protein and salt, combined with a normal calcium intake, provides greater protection than the traditional low calcium diet
Borghi et al. NEJM 2002
Thiazide diuretics
• Decreases urine calcium excretion and reduces rates of Ca stones by >50% in a 3 year period1,2,3,4
• Concurrent low salt diet (attenuates urinary calcium excretion) and sufficient potassium (to avoid hypocitraturia)5
1Borghi et al. J Cardio Phamacol 1993 2Ettinger et al. J Urol 1988 3Laerum et al. Acta Med Scand 1984 4Fernandez-Rodriguez et al. Actas Urol Esp 2006 5Pak et al. AJM1985
Potassium Citrate • Reduces stone recurrence among patients with
hypocitraturia1,2
• Can be safely combined with a thiazide • Lowers urinary calcium excretion, raises urinary
citrate and reduces urinary CaOxalate, CaPhosphate and undissociated uric acid supersaturation3.
1Ettinger et al. J Urol 1997 2Barcelo et al. J Urol 1993
3Sakhaee et al. KI 1983
Allopurinol
• Decreases stone recurrence in patients with idiopathic CaOxalate stones with hyperuricosuria
• Should be paired with a reduction in purine intake
Approach to evaluation & Rx of kidney stones First stone Recurrent stone
24 Urine Collection
High/N Calcium
Blood test
Uric Acid >750mg/day (women)
>800mg/day (men) Oxalate <40mg/day
Citrate <550mg/day (women) <450mg/day (men) Calcium
>250mg/day (women) >300mg/day (men)
Urine Vol <2L High PTH
Hyperparathyroidism
Bicarbonate
RTA
Progressive calculi (increasing in size or number) Children, Non-caucasians Non calcium containing calculi Solitary kidney xt
Increase fluid intake Aim UV >2L/day Lower salt intake
Thiazide
Urine pH <6.5
Potassium Citrate Low oxalate diet ↑Calcium in diet
↓Purine diet Weight loss Allopurinol
UTI? Rx UTI
Imaging Imaging
Low/Low N
Yes
No
No
Yes Labs
Summary • Renal stones is increasing in incidence • First timers may not need to be evaluated, however • Further evaluation is necessary in certain circumstances
o Multiple/recurrent stones o Progressive calculi (increasing in size or number) o Children, Non-caucasians o Non calcium containing calculi o Solitary kidney o Metabolic syndrome
• In the acute setting medical therapy can be attempted (if stones are <7mm) and surgical options pursued if needed
• General advice to increase fluid intake, salt/oxalate/animal protein restriction and normal calcium diet is applicable to most patients
• Further treatment options can be tailored based on biochemical findings
• Follow-up is required to avoid long term sequelae from chronic renal calculi
Recommended reading
• Elaine M. Worcester and Fredric L. Coe.Calcium Kidney Stones.NEJM 2010;363:954-63.
• Khashayar Sakhaee, Naim M. Maalouf, and Bridget Sinnott. Kidney Stones 2012: Pathogenesis, Diagnosis, and Management. J Clin Endocrinol Metab 97: 1847–1860, 2012.