Urolithiasis and Frequent CT Scans: Does Chronic Pain Play a Role?

Abstract

Introduction:

Urolithiasis is among the top 10 causes of Emergency Department (ED) visits in the United States. Approximately 50% of these patients undergo abdominopelvic CT scan, many more than once. We hypothesized that chronic pain conditions may contribute to frequent CT scans in patients who are evaluated in ED for urolithiasis.

Methods:

A retrospective review of patients presenting to our tertiary care and the associated satellite EDs for urolithiasis, during the period 12/2012–05/2013, was performed. Patients with multiple ED visits and two or more abdominopelvic CT scans in any 6-month period were labeled as the frequent CT group. Control group consisted of similar patients who had no more than one CT scan in any 6-month period. Background information, number of CT scans for urolithiasis and other reasons, and the presence of chronic pain (established pain clinic visits, chronic pain medication, known chronic pain syndromes) were captured from charts. Wilcoxon rank-sum test and Fisher's exact test were used to compare variables. Multivariable logistic regression was performed to identify predictors associated with frequent CT scans.

Results:

We identified 185 patients with frequent CTs and 139 patients in the control arm. Frequent CT scans were independently associated with chronic pain (odds ratio [OR]: 2.67, confidence interval [95% CI]: 1.55, 4.50), age (OR: 0.73, 95% CI: 0.60, 0.89), history of prior urolithiasis (OR: 2.15, 95% CI: 1.11, 4.15), and Medicaid insurance status (OR: 3.94, 95% CI: 1.66, 9.35).

Conclusion:

Chronic pain is a significant contributing factor to frequent CT scans among patients presenting to ED with urolithiasis, leading to increased radiation exposure and healthcare costs.

Introduction

Exposure to medical ionizing radiation has significantly increased in the past few decades, with an increase from 15% in 1980s to 48% in mid-2000s of total ionizing radiation exposure for the population of United States being attributed to medical purposes. The major factor has been increased use of CT scanners and nuclear medicine, with these two imaging modalities contributing 75% of medical radiation exposure of the U.S. population.¹

Kidney and ureteral stones constitute a significant cause of Emergency Department (ED) visits in the United States, with incidence increasing from 289 to 306 per 100,000 individuals from 2006 to 2009 and a total of ∼3.63 million visits in that period.² CT scan has had an increasing role as the study of choice for evaluation of suspected renal colic in EDs and elsewhere. Close to half of the patients (42.5% in 2007) who presented to ED with suspected urolithiasis will have a CT scan, which has shown a 10-fold increase compared with 1990s.³ Many patients present to ED multiple times and in the process will have more than one CT scan,⁴ which can sometimes accumulate to significant numbers over time. Since pain is a major reason for ED visits and also a hallmark of renal colic, we hypothesized that chronic pain conditions may contribute to frequent CT scans in patients who are evaluated in ED for urolithiasis. We sought to determine whether an underlying chronic pain condition could be a trigger for the acquisition of multiple CT scans in patients suspected of having a renal colic episode.

Methods

At our urban academic tertiary care institution, we maintain an Institutional Review Board (IRB)-approved database of all patients with urinary stone disease who have presented to our center and its satellite facilities. We retrospectively identified all the patients who had presented to any of the Cleveland Clinic EDs in Ohio and Florida with a primary diagnosis of urolithiasis (ICD-9 codes 592.1, 592.9) within December 2010 to May 2013 and had received a CT of the abdomen and pelvis during that visit, a total of 5036 patients. Among this group, we identified those patients who had more than one ED visit and ≥2 abdominopelvic CT scans performed within a 6-month period—the frequent CT group. To compare, our control group consisted of patients who likewise had more than one ED presentation (at least one urolithiasis visit) within the same period and only received one CT scan within any 6-month period of that time frame. A meticulous chart review of every patient in both frequent CT overuse and control groups was performed and parameters such as age, gender, ZIP code (to calculate median income based on published averages), number of ED visits, past medical and surgical history (including abdominal surgeries), and psychological history (including mood disorders, psychotic disorders, and alcohol and substance abuse), as well as medical insurance status (no insurance, Medicaid, Medicare, private), were captured. In addition, complete urologic history with specific focus on the presence of routine stone disease follow-up and number/type of stone-related procedures, including extracorporeal shockwave lithotripsy (SWL), ureteroscopy, percutaneous nephrostolithotomy (PCNL), and other stone surgeries, as well as other pain-inducing conditions (e.g., polycystic kidney disease and ureteropelvic junction obstruction), were recorded. We then identified patients who suffer from a chronic pain condition; in our study, chronic pain patients included established patients treated by a pain management clinic for chronic pain (managed by chronic pain providers with nerve blocks, medications, etc., for a painful condition on a regular basis and not just a single visit); chronic users of pain medications, including long-acting narcotics, tramadol, and gabapentin (except when given for pure diabetic neuropathy); and existing diagnosis of chronic pain syndromes (e.g., chronic painful myalgia, polymyalgia, chronic painful radiculopathies). We did not include emotional or psychological issues under this category; however, we did separately include mood disorders and psychotic disorders in our analysis, as reported in Table 1.

Table 1.

Descriptive Statistics for Both Groups

	Control (N = 139)	CT overuse (N = 185)	p
Mean age (years)	50	43	<0.001^a
Gender (male:female)	60:79 (43% vs 57%)	67:118 (36% vs 64%)	0.209
Median income (US$)	44,809	44,345	0.237^a
Medical insurance, n (%)
Uninsured	24 (17)	22 (12)	<0.001
Medicaid	17 (12)	64 (35)
Medicare	33 (24)	35 (19)
Private	65 (47)	64 (35)
Mood disorders, n (%)	25 (18)	62 (34)	0.002
Psychotic disorder, n (%)	7 (5)	15 (8)	0.373
Alcohol/narcotic abuse, n (%)	5 (4)	19 (10)	0.031
Prior abdominal surgery, n (%)	54 (39)	92 (50)	0.056
Regular urologic follow-up, n (%)	74 (53)	83 (45)	0.145
Prior urolithiasis, n (%)	20 (14)	41 (22)	0.086
Multiple punctate renal calculi on CT, n (%)	52 (37)	94 (51)	0.018
History of SWL, n (%)	26 (19)	40 (22)	0.578
History of URS, n (%)	33 (24)	66 (36)	0.028
History of PCNL, n (%)	5 (4)	10 (5)	0.595
History of UPJO, n (%)	3 (2)	3 (2)	1.000
History of ADPKD, n (%)	0 (0)	3 (2)	0.263
Chronic pain, n (%)	35 (25)	92 (50)	<0.001
Pain clinic	16 (12)	62 (34)	<0.001
Long-term pain meds	43 (31)	92 (50)	<0.001

Wilcoxon rank-sum test, otherwise Fisher's exact test was used.

ADPKD = autosomal dominant polycystic kidney disease; PCNL = percutaneous nephrostolithotomy; SWL = extracorporeal shockwave lithotripsy; UPJO = ureteropelvic junction obstruction; URS = ureteroscopy.

We recorded the total number of abdominopelvic CT scans performed for each patient from the beginning of the period up to March 2016 as well as number of CTs ordered by ED (total and specifically for urolithiasis), by urology service, and by other services for various reasons. The presence of numerous bilateral nonobstructive renal calculi on CT scan and whether or not a follow-up kidney/ureter/bladder radiograph (KUB) and/or renal sonogram (RUS) had been done within 30 days after the stone-related CT were recorded.

Statistical analyses

Baseline variables were summarized with the use of descriptive statistics. Continuous variables were described with median and interquartile range. Categorical variables were described with counts and percentage. The Wilcoxon rank-sum test was used to compare continuous variables and Fisher's exact test was used to compare categorical variables. A multivariable logistic regression was performed to identify predictors associated with frequent CT scans. The number of covariates for the multivariable model was selected to avoid overfitting and collinear variables were removed. Age, gender, presence of multiple bilateral nonobstructive stones, a diagnosis of chronic pain, history of mood disorder, prior abdominal surgery, regular stone follow-up, prior stone disease, and insurance status were carried over to the final model. The model was assessed with the C statistic and Hosmer–Lemeshow goodness-of-fit test. All results were considered significant at the level of a = 0.05. Statistical software package R (Core Development Team, Ver. 3) was used for all analyses.

Results

Overall, we identified 185 patients with frequent CTs and 139 patients in the control arm. Table 1 shows the descriptive statistics between the two groups. We found that patients in the frequent CT group tended to be younger (43 years vs 50 years, p < 0.001), more likely to have multiple bilateral kidney stones (51% vs 37%, p = 0.018), and more likely to have had a history of ureteroscopy for stone disease (36% vs 24%, p = 0.028). Mood disorders such as anxiety, major depression, and other nonpsychotic mental problems (p = 0.02), as well as history of ethanol or illicit narcotic abuse (p = 0.031), were also significantly more common in the frequent CT group. There was a significant association between the insurance type and frequent CT use (p < 0.001).

Patients receiving frequent CTs were more likely to be on chronic pain medication (50% vs 31%, p < 0.001) and being managed by pain clinic for chronic pain issues (34% vs 12%, p < 0.001). Overall, having a chronic pain condition, as defined by those variables and patient's history, also was significantly more common in frequent CT patients (50% vs 25%, p < 0.001). There were no significant differences between the two groups in terms of gender (male-to-female ratio), median household income (calculated based on ZIP codes), prevalence of psychotic disorders (schizophrenia, bipolar disorders, etc.), prior abdominal surgery, SWL, PCNL, or the presence of ureteropelvic junction obstruction or polycystic kidney disease. In addition, we did not find any significant difference in the rate of follow-up KUB or RUS in a 30-day period following CT scan, indicating urolithiasis.

Our results show that kidney stone patients with chronic pain are more predisposed to overexposure to ionizing radiation due to having more frequent CT scans over time. Our frequent CT group patients had a median of five CT scans (range: 2–34 scans) compared with a median of two for controls.

In the long-term, beyond the 6-month window, those patients who were frequently scanned within 6 months also accumulated more CTs in total as well as those specifically performed for urolithiasis (Table 2).

Table 2.

CT Scans of Abdomen and Pelvis Among Both Groups

	Control (N = 139)	CT overuse (N = 185)	p^a
CTs by all	2 (1–3)^b	5 (4–8)	<0.001
CTs by ED	1 (1–2)	4 (3–7)	<0.001
CTs by ED for urolithiasis	1 (1–1)	3 (2–5)	<0.001
CTs by others	0 (0–1)	1 (0–2)	<0.001
Follow-up KUB in 30 days, n (%)	15 (11)	31 (17)	0.149
Follow-up RUS in 30 days, n (%)	11 (8)	21 (11)	0.35

Tests used: Wilcoxon rank-sum test for all.

Median (interquartile range) shown for all rows.

ED = Emergency Department; KUB = kidney/ureter/bladder radiograph; RUS = renal sonogram.

Using multivariable modeling, we controlled for age, gender, presence of multiple bilateral nonobstructive stones, history of mood disorder, history of prior abdominal surgeries, having regular follow-up for stone disease, history of prior stones, and insurance status (C statistic: 0.76; Hosmer–Lemeshow goodness-of-fit test: 0.42). Chronic pain remained independently associated with receiving frequent CT scans (odds ratio [OR]: 2.67, confidence interval [95% CI]: 1.55, 4.50). In addition, age (OR: 0.73, 95% CI: 0.60, 0.89), history of prior urolithiasis (OR: 2.15, 95% CI: 1.11, 4.15), and Medicaid insurance status (OR: 3.94, 95% CI: 1.66, 9.35) were also significantly associated with receiving frequent CT scans (Table 3).

Table 3.

Multivariate Analysis

	Odds ratio (95% confidence interval)	p
Age (per 10 years)	0.73 (0.60, 0.89)	0.0017
Sex (M:F)	1.21 (0.69, 2.11)	0.448
Nonbstructive renal calculi	1.63 (0.98, 2.72)	0.0587
Chronic pain	2.67 (1.55, 4.5)	0.0004
Mood disorders	1.64 (0.90, 2.99)	0.1001
Prior abdominal surgery	1.60 (0.92, 2.78)	0.0927
Regular urologic follow-up	0.66 (0.39, 1.12)	0.128
Prior urolithiasis	2.15 (1.11, 4.15)	0.0217
Insurance:
Uninsured	Reference
Medicaid	3.94 (1.66, 9.35)	0.0018
Medicare	1.66 (0.64, 4.24)	0.2893
Private	1.09 (0.51, 2.30)	0.8145

F = female; M = male.

Discussion

One of the major reasons for visiting the ED in general is pain, and renal colic, as one of the primary manifestations of urolithiasis, can commonly result in patients seeking help from ED. As mentioned before, approximately half of these patients will be evaluated with a CT scan as the initial study. Based on our results, of all the patients who present to ED due to urolithiasis and undergo a CT scan for evaluation, those who do have an existing chronic pain condition will over time accumulate a significantly more number of CT scans. When observed during a period of time, these patients in fact have a 2.5-fold median number of abdominopelvic CT scans compared with the nonchronic pain urolithiasis patients as shown in Table 2. The CT scans are most frequently generated by subsequent visits to ED compared with other providers.

It has previously been shown that frequent ED use is associated with Medicaid insurance, mental illness, and also frequent ED use in prior year.⁴ This is in concordance with our results. We also report on other factors, which increase the likelihood of undergoing frequent CT scans in addition to chronic pain: patients with prior urolithiasis history, Medicaid insurance, and those who are younger at the time of their initial ED stone visit. This latter finding may be partially explained by the notion that in general older patients perceive less visceral pain.⁵

In a study of radiation exposure as a result of urolithiasis diagnosis and management in two academic centers, Ferrandino and colleagues reported 20% of patients receiving greater than 50 mSv of total effective radiation dose during 1 year.⁶ Universal guidelines for maximum medical radiation exposure have not been established; however, the maximum limit for occupational radiation exposure is 50 mSv per year and 400 mSv for lifetime.⁷ A recent meta-analysis of 50 articles on radiation exposure during nephrolithiasis evaluation and management reports an average of 10 to 20 mSv per each noncontrasted CT scan and lower amounts (1.4 mSv in males, close to 2 mSv in females) for low-dose CT scans.⁸

In addition to radiation hazard, frequent CT scans will lead to increased healthcare costs. Kidney stones are among the top 10 reasons for ED visits in the United States, and in a large study of >8000 ED encounters, the median charge for kidney stone visit was shown to be $3437 (95% CI: $2917, $3877), the highest cost among all visit reasons by a wide margin.⁹ Coexisting chronic pain and urolithiasis can therefore result in significant increase of healthcare costs through multiple CT scan and ED visit costs, in addition to additional costs such as pain clinic visits, chronic analgesic requirements, and possible nerve blocks.

Limitations of our study include its retrospective design, possible omission of patients due to differences in ICD-9 coding of diagnoses in ED, and comprising single-center data.

Conclusion

The presence of chronic pain is a significant contributing factor to frequent CT scans among patients who present to ED with urolithiasis. As a consequence, frequent CT scans will lead to increased radiation and increased healthcare costs. Clinicians should be mindful of their urolithiasis patients' comorbidities, including chronic pain, as well as their prior radiological evaluations.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Abbreviations Used

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