Ureterolthiasis has become a poster child for over-utilization of advanced imaging. Despite the relative level of distress kidney stones cause our patients, the use of computed tomography has never been associated with improved outcomes – yet, CT is widespread for its diagnostic utility, contributing substantially to $2 billion in annual healthcare expenditures for this condition in the U.S. alone.
This, however, is a comparative effectiveness evaluation promoting ultrasound for the diagnosis of ureterolithiasis in the Emergency Department, a three-pronged evaluation comparing CT, formal ultrasonography by radiology technicians, and bedside Emergency Department ultrasonography. Essentially, the objective of this study was to compare safety – regarding, in a sense, whether the additional information supplied by CT was valuable for the detection of life-threatening alternative diagnoses. And, with respect to this outcome all strategies had, essentially, the same number of “misses” during the follow-up period – mostly acute cholecystitis, one case of appendicitis, and a smattering of other thoracoabdominal diagnoses. And so – ultrasonography, even our amateur sort in the ED, is “just as good”.
Of course, there are a few oddities associated with this publication. There are, bizarrely, three “primary outcomes”, and the authors explicitly choose to report only two of them. Total costs of care was intended to be an outcome, but the authors simply state those results will not be reported in this paper. This study also has an interestingly low incidence of ~33% confirmed ureterolithiasis – which may result from their lack of a “gold standard” for diagnosis of stone, relying on patient-reported stone passage or follow-up for stone removal. Or, it could be enrollment of a population with an oddly low incidence of hematuria – only ~63% of enrolled patients exhibited this common finding with a sensitivity of >80%. I’d be curious to see the incidence of hematuria in the cases with alternative diagnoses, although there would likely be too few to draw any substantial conclusions.
There was also substantial crossover from the ultrasonography cohorts. 40.7% of those randomized to ED ultrasonography and 27.0% randomized to radiology ultrasonography ultimately underwent CT. And, this crossover reveals the limitation of ED ultrasonography: a “sensitivity” of 54%, compared with a “sensitivity” of 88% for CT (the unreliable gold standard for diagnosis limits test characteristic calculations). There was also a major exclusion relevant to the U.S. population: women over 250 lbs and men over 285 lbs. Unfortunately, a substantial portion of the U.S. exceeds such superlative mass – and the generalizability of these results to that population is open to reasonable variability.
The take home point, however, is a little less reliable. Yes, if you select patients for imaging similarly to these authors and visualize unilateral hydronephrosis in the setting of suspected ureterolithiasis, it is fair to terminate your diagnostic pathway. However, the primary fallacy of this study design is predicated on the debatable necessity of performing imaging for all suspected ureterolithiasis. One can make a very reasonable argument ureterolithiasis can be adequately diagnosed on clinical grounds, and advanced imaging is required only in the minority of cases, regardless of the findings on bedside ultrasound. The vast majority of ureterolithiasis carries a relatively benign prognosis of recurring and remitting pain of a few weeks duration, and return precautions or outpatient follow-up for persistent symptoms is likewise a reasonable course of action.
“Ultrasonography versus Computed Tomography for Suspected Nephrolithiasis”
http://www.nejm.org/doi/full/10.1056/NEJMoa1404446
"This study also has an interestingly low incidence of ~33% confirmed ureterolithiasis"
This is difficult to understand. Renal colic is usually a very straightforward diagnosis, with some very rare dreadful pitfalls.
I would have "guesstimated" a figure well above 85%
I would hasard the doctor in the study doth suspect the diagnosis too much.
But the standard is a difficult one , I don't expect 100 % of patients complying with the "urinate in a filter or bottle and retrieve the stone" instructions.
Does the fact that there is no significant difference betwen the ED-US-ed vs Radiology -US-ed vs CT scanned groups reflect :
– the fact that US does as well as CT (we know and it also appears in this study that US misses stones a lot and likely also distension.)
– or the fact that whatever the patient had it was mostly benign, and imaging can't significantly change this when badness-type renal colic (RC) mimics are so rare ?
– or both ?
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"The vast majority of ureterolithiasis carries a relatively benign prognosis of recurring and remitting pain of a few weeks duration, and return precautions or outpatient follow-up for persistent symptoms is likewise a reasonable course of action. "
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What is the incidence of painless yet obstructing stone that may silently destroy a kidney ? Or both ?
(poor meaning anectdote : I have a chilling remembrance of a family case with typical right sided RC, seen at St Elsewhere ED, a creatinin level is drawn: 400 µmol/L estimated Creatinin clairance around 20 mL/min. CT shows bilateral obstructive stone.)
Because if we don't image typical cases especially in frequent stoners in the ED I think imaging has to be done 2-4 weeks later to check there s no obstruction , if the stone hasn't been passed, and even this may miss the remaining second stone. I don't know of any data in support of what I say though.
I think one of the flaws that's apparent – not in the paper, but in our general practice in the U.S. – is the perceived necessity of the _confirmatory_ test, rather than the _diagnostic_ test. In this study, it's pretty clear, if alternative diagnoses are only minimally suspected – appendicitis, bowel issues, AAA – adverse outcomes will be low, regardless of management. Testing, then, is simply to confirm ureterolithiasis. There reasonable scenarios in which making such an initial diagnosis is prudent, or to describe possible complications of stone presence, but this is a benign condition frequently diagnosed (or misdiagnosed!) in resource austere settings without serious untoward outcomes.
The question re: bilateral obstructing stones is important, thus ultrasound should evaluate both kidneys, even in the setting of unilateral symptoms.
Do you have know of any studies looking at not imaging clinically obvious renal colic at all?
I know I read some in the past, and have been practicing this way for years, but can't seem to find them now.
Cheers
Justin
I don't know of any, specifically, but when you look at the STONE score and compare it with the elements of clinical history/presentation that factor into gestalt, it's reasonable to say there are some patients for whom gestalt will be >90% accurate.
I, too, have been practicing imaging-free diagnosis of renal colic. Most will do well. Some will return and need imaging for failure of pain control, and ultimately urologic intervention. Important alternative diagnoses are quite rare, however.