Download Week 5: Nephrolithiasis

NEPHROLITHIASIS
Jacqueline Satchell-Jones, M.D.
WEEK 5: 01/31 – 02/04/05
Learning Objectives:
1. Describe the historical, radiographic, and laboratory features consistent with
kidney stone
2. Describe how metabolic work-up differs in a patient with initial vs. recurrent
stones
Editor’s Note:
A special thank you to Rebecca Brienza, MD, who was the original author of
this chapter, which has been adapted here.
CASE ONE:
Mr. Stone is a 37-year-old Caucasian truck driver who presents to you with sudden
onset of severe right flank pain that travels to his lower abdomen and right groin
area. He states that it began two days ago and he has been experiencing waves of
nausea, but no vomiting. He cannot recall any trauma. He denies any change in his
bowel habit, but does note mild dysuria and occasional urinary frequency. The pain
does not change with position or breathing. He took a few acetaminophen without
pain relief. He is mildly obese and has GERD, hypertension and diabetes. His
medications include hydrochlorothiazide, metformin, vitamin C, and antacids. He
denies having any prior gastrointestinal problems, no surgery, and no urinary tract
infections. He remembers having similar pain at age 20 but did not see a doctor for
it. You believe this patient has kidney stones and send him to the lab for a
urinalysis.
Questions:
1. a. Explain what features of the patient’s history and presentation are
consistent with nephrolithiasis?
The cardinal manifestation of renal colic is excruciating unilateral flank pain
or lower abdominal pain of sudden onset, not related to any precipitating
event (such as muscle strain or trauma, malignancy), not relieved by postural
changes or over the counter pain meds. With the exception of nausea and
vomiting, GI symptoms should be absent. The pain sometimes radiates to the
lower abdomen and ipsilateral groin. If the stone is distal, the patient may
have GU symptoms such as dysuria, frequency, urgency, bloody urine, etc.
b. What else should you consider in the differential diagnosis for this patient
and would it be different if this patient were a woman?
One needs to consider in the DDx for this patient the following: hepatitis,
pancreatitis, appendicitis, gallstones, hernia, diverticulitis, and blockage in
the intestine, AAA, testicular or prostate pathology.
If this patient were a woman, you must do a pelvic exam (and a urine
pregnancy test) to evaluate for, gynecologic pathology such as ectopic
pregnancy, PID, ovarian torsion, and ovarian cyst.
c. Explain what you will be looking for in the urinalysis, and why?
Findings to look for on the urinalysis include: microhematuria (1/3 of patients
with kidney stones do not have blood); urine pH suggests the type of stone that
may be present (pH<7: uric acid or cystine stones; pH>7: infection, calcium
phosphate/struvite stones). Infection should also be ruled out. Limited pyuria
is common with stones but, in the absence of bacturia, is generally not
indicative of a UTI.
CASE ONE CONTINUED:
The patient returns from the lab with the urine dipstick showing 2+ blood and a
pH of 8.0. The micro showed >100 RBC, 10-15 WBC, and few bacteria. Urine
culture is pending.
2. How would you confirm your diagnosis?
Confirm kidney stone with an imaging modality, of which there are several, each
with advantages and disadvantages:
This patient’s urinalysis is alkaline which may suggest a calcium stone, which
would appear radio-opaque on plain X-ray. The limiting factor with plain film is
that the sensitivity is poor (about 50%) due to poor visibility from stool and bowel
gas.
Prior to non-contrast helical CT, IVP was considered the definitive study to
confirm kidney stones. IVP has high sensitivity and specificity, provides
information on anatomy and functioning of the kidneys; however, it requires use
of IV contrast with risk of nephrotoxicity. IVP does not detect non-GU pathology
and may not produce a filling defect if non-obstructing radiolucent stones are
present.
This patient has diabetes and is on metformin and a diuretic, and so IVP would
not be a good choice for him due to the risk of fatal metabolic acidosis and an
increased risk of nephrotoxicity. If one needs to do an IVP (i.e. CT not available),
the patient should be well hydrated, metformin needs to be stopped 24 hours prior
to the planned date and restarted 48 hours after this procedure.
An ultrasound is useful to rule out obstruction or hydronephrosis and is usually
readily available. It is sensitive in identifying renal calculi but not ureteral stones,
which are more likely to be symptomatic.
Non-contrast helical CT is the imaging study of choice for this patient. It is fast,
accurate, readily identifies all stone types in various locations, and is safe. Its
sensitivity and specificity is over 95%. Helical CT’s advantages come at a higher
cost compared to an IVP.
CASE ONE CONTINUED:
After confirming that the patient has a stone (3.5mm in the distal portion of the
right ureter, with no hydronephrosis) you send him home with NSAIDs, a strainer,
and a recommendation to drink lots of fluids.
3. Describe your approach in working up the cause of kidney stones after the
first presentation. Describe any additional evaluation you would do in a
recurrent stone former.
First, review the patient’s history for risk factors that might predispose him to
stone formation: e.g. his race and occupation (e.g. truck driver); HTN on a
diuretic (esp. furosemide, ethacrynic acid); and antacids to treat his reflux sxs,
which can change the urine pH, and make it more alkaline.
Some other risk factors to consider include:
Intestinal disease—such as Crohn’s or ulcerative colitis, chronic diarrhea,
leukemia/lymphoma, chemotherapy, thyroid meds, large doses of vitamin C, prior
urinary or bladder infections, blood relatives with kidney stones (45% of calcium
stone formers have a genetic basis), gout or family history of gout, sarcoidosis, or
parathyroid problems. Patients with AIDS on a medication combination, which
includes indinavir, zidovudine, or lamivudine have >35% risk for kidney stones.
Patients with stones less than 4mm should pass their stone in 1-2 weeks and
generally, require no intervention other than analgesia. The fact that this
patient’s stone is in the distal ureter is a good sign. An imaging study should be
performed within the first 2 weeks to confirm the stone has completely passed. If
the stone has not passed or is large (>5mm) the patient needs referral to the
urologist.
The recurrence rate for patients who pass a calcium stone is about 50% by ten
years. However, since the course of most stones is quite indolent, most
recommend a limited work-up after the first calcium stone and dietary/lifestyle
modifications that would be recommended independent of a stone (e.g. maintain
good hydration, limit excessive red meat consumption). One approach to “first
stones” is to check a serum calcium in patients with radio-opaque stones and a
serum uric acid in those with radiolucent stones.
Patients with recurrent stones require a more detailed metabolic work-up.
This would include: serum electrolytes, BUN, creatinine, calcium to screen for
hypercalcemia (hyperparathyroidism, most common in women with calcium
stones, or malignancy), uric acid to screen for hyperuricemia , magnesium,
phosphate, a cbc, lfts, pregnancy test if female. Obtain two 24-hour urine
collections with Mr. Stone on a normal diet and fluid intake while stopping his
thiazide diuretic. The urine should be checked for volume, calcium, uric acid,
citrate, oxalate, creatinine, pH, and sodium. Measurement of 24-hour urinary
sodium excretion is important. One can achieve low urinary calcium and uric
acid levels, and fewer stones, either through volume depletion or a low sodium
diet. Elevated urinary sodium suggests that the patient should ensure adequate
volume and ensure a low sodium diet.
Normal values for 24-hour urinary excretion
Calcium
Uric Acid
Citrate
Oxalate
Creatinine
Men
<300 mg
<800 mg
450-600 mg
<45 mg
20-45 mg/Kg
Women
<250 mg
<750 mg
650-800 mg
<45 mg
5-20 mg/Kg
Hypercalciuria is the most common cause of calcium stones and is felt to be due
to an increased GI absorption in patients with recurrent stones. Can check a 1,25
OH vit D level. Hypocitriuria is another major contributor to calcium stones.
Calcium phosphate stones are most likely due to renal tubular acidosis. Patients
with non-calcium stones usually have identifiable metabolic disorder.
4. If the patient were 55 years old with a calcium stone and taking calcium
supplements “for her bones” would you tell her to stop?
Not necessarily. It has been fairly well established that dietary calcium is
protective against calcium oxalate stones (dietary calcium binds oxalate).
Therefore, we would like her to get more of her daily calcium from dietary
sources (perhaps, a bowl of Total each morning). In one study, women who took
calcium supplements had a 20% higher risk for stones. This may be because the
supplements were taken without food, which resulted in less binding of oxalate
and more oxalate in the urine. So, she can continue to take calcium supplements
(up to 1200 mg/day) with food or simply make an effort to meet those
requirements with more dietary calcium.
References:
1. Parmar, M.S. Kidney stones. BMJ. 2004; 328:1420-1424.
Additional References:
1. Portis, Andrew J, M.D., and Sundaram, Chandru P., M.D. Diagnosis and
initial management of kidney stones. American Family Physician. 2001;
Vol.63, Num.7:1329-1338.
2. Goldfarb, David, M.D. et al. Prevention of recurrent nephrolithiasis. American
Family Physician. 1999. 60:2269-2276.