Kidney stones
Agnieszka Bankowska-Brukasz M.D.
Kidney stones
Common problem in primary care practice Patient may present: classic symptoms (renal colic & hematuria), asymptomatic or have atypical symptoms (vague abd. pain, acute abd.pain, nausea, dysuria, penile pain, testicular pain). PMD need to be alert to the possibility of urolithiasis and its consequences to decide upon a diagnostic approach, therapy, and the need for referral to urologist.
Epidemiology
Prevalence 2-3% in general population Estimated lifetime risk about 12% for men 5% for women Approximately 50% of patient with previous urinary calculi have recurrence within 10 years. The rate of urolithiasis increases with age, is higher in men compared to women, and whites compared to blacks. Hispanic and Asian are at intermediate risk. It has been estimated that 7-10 of every 1,000 hospital admission are due to stones.
Etiology
60-80% calcium stones
(Ca oxalate > Ca phosphate)
15-20% struvite
(magnesium ammonium phosphate)
5% uric acid 1-3% cystine The same patient may have more than one type of stone concurrently (e.g.. calcium and uric acid).
Etiology cont…
Stone formation occurs when normally soluble material (e.g.. Ca) supersaturates the urine and begins the process of crystal formation. It is not clear how crystals formed in the tubules become a stone, rather than being washed away by the high rate of urine flow. It is presumed that crystals aggregates become large enough to be anchored ( usually at the end of the collecting ducts), and then slowly increase in size over time.
Risk factors
History of prior calcium urolithiasis (One report of
patients with a first stone estimated that the likelihood of forming a second stone was approximately 15 % at 1yr, 35-40% at 5 yrs, and 50% at 10 yrs.)
Family history of urolithiasis Dehydration and consequent increase urine concentration Increase enteric absorption of oxalate (short bowel
syndrome)
UTI Medication that promote crystalluria (Sulfadiazine, Triamteren, Indinavir, Acetazolamide)
Risk factors cont…
Hypertension – risk of stone formation incr. x2 (? hypercalciuria?) S/p vasectomy Dietary habits - soft drinks acidified with phosphoric acid increase calcium stone formation.. Mechanism ? Possible that small acid load can increase the urinary excretion of calcium and uric acid and reduce that of citrate. Coffee, tea,wine decrease risk of of stone formation grapefruit and tomato juice increase the risk.
Risk of urolithiasis cont…
Uric acid lithiasis - gout - hyperuricosuria - chronic diarrheal states Struvite stones –UTI due to urease + organisms(Proteus , Klebsiella) Cystine stones – Pt with cystinuria due to insolubility of cystine in the urine
Clinical manifestations
Patient may occasionally present after already having passed gravel or a stone. Symptoms are usually produced when stones pass from the renal pelvis into the ureter. Pain typically waxes and wanes in severity, and develops in waves or paroxysm that are related to movement of the stone in the ureter and associated with ureteral spasm.Paroxysm of severe pain usually last 20-60 min.
Clinical manif.cont…
The site of obstruction determines the location of pain.Upper ureteral or renal pelvic obstruction lead to flank pain or tenderness, whereas lower ureteral obstr. causes pain that radiate to ipsilateral groin.
Stone location and Symptoms
Stone location Kidney Prox. Urether
Middle section of urether
Common symptoms
Vague flank pain, hematuria Renal colic, flank pain, upper abdominal pain
Renal colic, anterior abd. pain, flank pain
Distal urether
Renal colic, dysuria, urinary frequency, anterior abd. pain, flank pain
Other symptoms :
nausea, vomiting, dysuria and urgency Complications: persistent renal obstruction, sepsis (instrumentation), renal failure (over the years if stones are present bilaterallystaghorn calculi).
Differential diagnosis
In women: any gyn. processesovarian torsion ovarian cyst ectopic pregnancy In men : testicular tumor epididymitis prostatitis Other causes of abd.pain: appendicitis, cholecystitis, diverticulitis, colitis, constipation, hernias, arterial aneurysms may elicit similar discomfort. Other causes of hematuria (GN)
Diagnosis
Focused history ( family history of calculi, duration and evaluation of symptoms, signs or Sx of sepsis) Clinical presentation Urinalysis Radiologic tests KUB, IVP, US, CTscan (including spiral CT)
Urinalysis
Should be performed in all patient with suspected calculi. Microhematuria, pH, crystals,bacteria Uric acid stones – acidic urine Infection – alkaline urine Limited pyuria is fairly common response to irritation caused by a stone, and in the absence of bacteriuria is not generally indicative of coexistent UTI.
Abdominal US
Sensitivty19%, specificity 97% Accessible Good for diagnosis of hydronephrosis and renal stones Poor visualization of ureteral stone. Procedure of choice for patients who should avoid radiation, including those with known allergy to IV contrast, pregnant women and woman in childbearing age.
KUB - Sens. 45-59% , Spec. 71-77%
Accessible and inexpensive. May be sufficient to document the size and location of radiopaque urinary calculi ( Ca oxalate, Ca phosphate), but not radiolucent stones such as pure uric acid, cystin or magnesium ammonium phosphate. Unfortunately stones are frequently obscured by stool or bowel gas, ureteral stones overlying the bony pelvis or transverse processes of vertebrae . Furthermore, nonurologic radiopacities, such as calcified mesenteric lymph nodes, gallstones, stool and phlebolits may be misinterpreted as a stones..
IVP – sens.64-87% , Spec.92-94%
Relatively safe despite the need for contrast Provides information about obstruction the stone (size, location, radiodensity) and degree of obstruction. Serum Cr must be measured before the test Nephrotoxic effect is minimized by adequate hydration, minimum amount of contrast material used. DM patient to stop Glucophage before the procedure and hold for next 48 hrs. May resume Metformin therapy after reevaluating renal function.
Noncontrast Helical CT
Fast, accurate, and readily identifies all stone types in all location. Sensitivity 95-100% , Specificity 94-96% Expensive ( ~600$ compared to 400$ for IVP) CT should not be used as a first line test in the evaluation of suspected urolithiasis unless the patient has abd. pain and an unclear diagnosis.
Recommended approach
Patient presenting with abdominal and flank pain who are suspected of having a kidney stone should first have a UA. If hematuria is present (r/o GN, no red cell casts or heavy proteinuria) order KUB in those without a history of urolithiasis. In contrast, no further evaluation in the emergency setting beyond the finding of hematuria is needed in patient with a known history of stones.
Treatment
Acute therapy IV hydration analgesics (NSAIDs - ketorolac) Narcotics – if no response to NSAIDs Patient can be managed at home if they are able to take oral medication and fluids. Hospitalization is required for those who cannot tolerate oral intake or have severe pain. Patient should be instructed to strain their urine and bring in any stone that passes for analysis.
First stone vs recurrent stones
Patient with first stone (symptomatic or asymptomatic) do not need metabolic evaluation other than a serum Ca in those with radiopaque stones and serum uric acid in those with radiolucent stones. Increase po fluid intake to 2L/d. Subsequent monitoring with KUB or US at 0 and 1year and if negative every 3-5 years thereafter.
Patient who have recurrent stones need a detailed metabolic and radiologic eveluation. Screening for hypercalcemia and hyperuricemia is indicated. Two 24-hour urine collection should be obtained in the outpatient setting when the patient is on regular diet. Urine volume and excretion of Ca, uric acid, citrate, oxalate,creatinine, pH, and Na should be measured.
Long term therapy should be initiated to prevent future stone formation. For calcium stones combination of drug therapy Thiazide for hypercalciuria, allopurinol for hyperuricosuria, K-citrate for hypocitraturia Uric acid stones – K-citrate to alkalinize the urine or Allopurinol Cystine stones – high fluid intake ,urinary alkalinization, and drugs such as penicillamine or captopril. Treatment with struvite stones is difficult, and usually requires ESWL or surgery.