Epidural Blood Patch does not Contribute to the Development of Chronic Low Back Pain in Patients who Undergo Lumbar Punctures: A Pilot Study

Abstract

Purpose of Review

Post dural puncture headache (PDPH) is a known and relatively common complication which may occur in the setting of patients undergoing lumbar punctures (LP) for diagnostic or therapeutic purposes, and is commonly treated with an epidural blood patch (EBP). There have been few publications regarding the long-term safety of EBP for the treatment of PDPH.

Recent Findings

The aim of this pilot study was to examine any association of chronic low back pain (LBP) in patients who experienced a PDPH following a LP, and were treated with an EBP. A total of 49 patients were contacted and completed a survey questionnaire via telephone. There was no increased risk of chronic LBP in the dural puncture group receiving EBP (percentage difference 1% [95% CI −25% – 26%], RR: 0.98 [95% CI 0.49 – 1.99]) compared to the dural puncture group not receiving EBP. There were no significant differences in the severity and descriptive qualities of pain between the EBP and non-EBP groups. Both groups had higher prevalence of back pain compared to baseline.

Summary

Our findings suggest that dural puncture patients undergoing EBP do not experience low back pain with increased frequency compared to dural puncture patients not undergoing EBP. Higher prevalence of LBP compared to baseline and compared to general population was seen in both groups. However, this pilot study is limited by a small sample size and no definitive conclusion can be drawn from this observation. The findings of this study should spur further prospective research into identifying potential associations between LP, EBP and chronic low back pain.

Introduction

Epidural blood patch is a commonly performed procedure to treat post dural puncture headache (PDPH). The long-term effects of EBP following LP have not been extensively studied. It is thought that PDPH is the result of a CSF leak that leads to low intracranial pressure and eventual sagging of the brain, cerebral blood vessel dilation, and dural tension.^1,2 Epidural blood patch (EBP) consists of injecting blood into the epidural space.³ This helps by forming a clot to plug the dural defect, restoring CSF pressure, and alleviating the headache.² EBP is the gold standard for treating PDPH that is resistant to conservative measures.^4–6 The goal of this pilot study was to evaluate the long-term effects of EBP on chronic low back pain.

Methods

This case-control pilot study was approved by the hospital institutional review board (Committee on Clinical Investigations). We have previously reported our findings on a cohort of patients who underwent obstetric anesthesia procedures who developed PDPH.⁷ This pilot study investigates the effect of EBP on back pain by comparing the prevalence of back pain in dural puncture patients who did not undergo EBP to dural puncture patients who required a subsequent EBP. Hospital ICD-9-CM procedure codes were queried to identify patients who underwent LP procedures at Beth Israel Deaconess Medical Center (BIDMC) during the period extending from January 1, 2003 to December 31, 2013. Eligible subjects were defined as patients who underwent these procedures and underwent a subsequent epidural blood patch (EBP). Once the subjects were identified, an eligible matched control group was created using the following variables: index procedure (LP), age at the time of intervention (± 10 years), and date of intervention occurring (± 6 months). Thus, the two groups were matched in all attributes but only one group had undergone an epidural blood patch.

All eligible subjects were first contacted via postal mail to notify of an impending phone call regarding this study. The patients were then contacted privately via telephone and invited to participate in a survey after informed consent. Up to three independent attempts were made to contact eligible subjects via telephone. Subjects who we were not able to contact were removed from further contact attempts. The results of all subjects who were contacted via telephone and consented to participate in the survey were presented. Patients, who were subsequently matched into the control group, were similarly contacted via telephone and invited to participate in the survey. The telephone interview consisted of a series of questions pertaining to low back pain. The primary outcome was chronic low back pain (LBP), defined as lasting greater than 6 months in duration. Secondary outcomes included low back pain lasting fewer than 6 months (LBP < 6), LBP frequency, LBP intensity, and LBP quality, effects of LBP on activities of daily living, treatments sought for LBP, and a history of diagnostic MRI for evaluation of the LBP.

Statistical Analysis

Descriptive statistics of the data were performed. Continuous data is represented as a mean (± SD). Variables not normally distributed as well as categorical data are presented using proportions. Chi square tests was used to evaluate differences in age, sex, race, ethnicity, and outcomes between patients using alpha ≤ 0.05. Fisher’s exact tests were used for all samples of 5 or fewer. All statistical analysis was performed using SAS v9.4 (SAS Institute, Cary NC).

Results

A total of 49 patients completed the survey questionnaire via telephone. There were 26 patients who underwent a LP and a subsequent epidural blood patch (EBP group). There were another 23 matched patients who underwent a LP, without a subsequent epidural blood patch (Non-EBP group).

There were no statistically significant differences between the groups for sex, race, mean age at the time of index intervention, years since spinal procedure at the time of the phone interview, and prevalence of self-reported pre-existing LBP. Mean follow up period at the time of interview was 10.3 years in the EBP group and 11 years in the non-EBP group (Table 1).

Table 1. Demographic Summary of All Patients Who Underwent a Lumbar Puncture, All N (%) Unless Otherwise Noted.

	EBP (N = 26)	Non-EBP (N = 223)	P Value
Sex (Female)	20 (77)	17 (74)	0.8
Race (Caucasian)	16 (62)	17 (74)	0.4
Mean age at spinal procedure (SD)	31.8 (10.2)	31.3 (10.2)	0.9
Mean years since spinal procedure (SD)	10.3 (1.7)	11.0 (1.7)	0.13
Preexisting LBP	4 (15)	3 (13)	1*

Note: *Fisher’s Exact.

Our primary outcome is reported in Table 2. No statistical significance was found in the number of patients in the EBP group that had new onset LBP following lumbar puncture procedure compared to patients in the non-EBP group (percentage difference 1% [95% CI −25% – 26%], RR: 0.98 [95% CI 0.49 – 1.99], P = 0 .96). Furthermore, no statistically significant difference was found in the number of patients in the EBP group that had new onset LBP < 6 following the index spinal procedure when compared to patients in the non-EBP group (percentage difference 3% [95% CI −24% – 28%], RR: 1.1 [95% CI 0.57 – 1.98], P = 0.85).

Table 2. Prevalence of Low Back Pain in Patients Who Underwent a Lumbar Puncture, All N (%).

	EBP (N = 26)	Non-EBP (N = 23)	P Value
LBP < 6	12 (46)	10 (43)	0.85
LBP	10 (38)	9 (39)	0.96

Abbreviations: LBP < 6 - combined Low Back or Low Back and Leg Pain Lasting Less Than 6 Months; LBP - Combined Low Back or Low Back and Leg Pain Lasting Greater Than 6 Months.

Amongst patients who reported LBP, there were no statistically significant differences between the EBP and non-EBP groups in the proportion of subjects who reported pain on average greater than 5/10 in severity on the VAS, pain that limited day to day activities, and pain that limited sleep. There were no statistically significant differences between the two groups in the proportion of patients receiving chiropractic care, physical therapy, acupuncture, or lumbar spine surgery. Additionally, there were no statistically significant differences amongst both groups in the medications trialed for management of the LBP, nor in those who obtained a diagnostic MRI for management of their LBP.

We did observe a notable increase in the number of patients requiring back or spine injections in the non-EBP group when compared to the EBP group with a percentage difference of 44% (Table 3).

Table 3. Prevalence of Pain Severity Markers in Patients Reporting Low Back or Combined Low Back and Leg Pain Lasting Greater Than 6 Months (%) Unless Otherwise Noted.

	EBP (N = 10)	Non-EBP (N = 9)	P Value
Average pain rated > 5/10	7 (70)	5 (56)	0.65*
Pain limits daily activity	7 (70)	7 (78)	1*
Pain limits sleep	6 (60)	7 (78)	0.63*
Descriptive quality of pain
Burning	3 (30)	3 (33)	1*
Aching	7 (70)	7 (78)	0.4*
Sharp	7 (70)	6 (67)	1*
Treatment Sought
Chiropractor	4 (40)	3 (33)	1*
Physical Therapy	5 (50)	4 (44)	1*
Acupuncture	1 (10)	2 (22)	0.58*
Neuropathics	2 (20)	5 (56)	0.17*
Muscle Relaxants	2 (20)	6 (67)	0.07*
Prescription anti-inflammatory	1 (10)	2 (22)	0.58*
Opiate	1 (10)	4 (44)	0.14*
OTC	6 (60)	8 (89)	0.3*
Back or spine injections	0 (0)	4 (44)	0.03*
Spine Surgery	1 (10)	0 (0)	1*
Lumbar MRI performed for evaluation of pain	3 (30)	3 (33)	1*

Note: *Fisher’s Exact Test.

We also observed increased prevalence of both LBP and LBP < 6 in both the groups; 38% and 46% respectively in the EBP group and 39% and 43% in the non-EBP group compared to the baseline. Preexisting LBP was 15% and 13% in the EBP and the non-EBP group.

Discussion

Dural puncture headache is a debilitating headache condition, for which EBP is the gold standard for treatment.^4–6 EBP is generally considered a safe procedure, though it can be associated with symptoms of transient back pain and stiffness. There are few studies investigating long-term effects of EBP on chronic low back pain. This pilot study found no significant difference in the rate of back pain amongst patients who received an EBP following a LP compared to back pain in patients who did not undergo an EBP following a LP. Conversely, our data demonstrated higher rates of chronic low back pain in both patient populations after LP.

In an epidemiological study using the NHANES database, 18.3% of US adults aged 30–39 years were identified as suffering from chronic low back pain.⁸ Another systematic review assessing the global prevalence of low back pain demonstrated one-month prevalence of 23.2% and an overall mean prevalence of 31.0% for LBP.⁹ Our study results demonstrated that 15% of the EBP group reported preexisting LBP (table 1) which increased to 38% of patients who experienced chronic LBP at the time of follow up. This result was also seen in the Non-EBP group with 13% of Non-EBP patients experiencing preexisting LBP (table 1) which increased to 39% for chronic LBP at the time of follow up. This finding may suggest that LP procedures may contribute to the development of chronic low back pain especially since the baseline numbers are close to the NHANES database. The findings of this study are similar to what Webb et al. reported. In their study there was also increased incidence of back pain in dural puncture patients but EBP was not found to be a risk factor for the development of low back pain.¹⁰ The pathophysiology of chronic LBP following a LP is not known. It is possible that an insult to the dura matter or the effect of CSF leak may lead to the development of chronic low back pain. Additionally, the headache that the dural puncture was likely performed for might herald development of chronic pain disorder, including back pain.

This pilot study demonstrated no statistical significance in the rates of new onset LBP between the EBP and Non-EBP groups (percentage difference 1%). There was also no statistically significant differences between the EBP and Non-EBP groups for subjects who reported pain on average greater than 5/10 in severity, limitations in daily activities, limitations in ability to sleep, the frequency with which they were limited in either daily activity or sleep, the quality of their pain, chiropractor therapy, physical therapy, acupuncture, and spine surgery (table 3). There were no statistically significant differences amongst both groups in the medications trialed for management of the LBP, nor in those who obtained a diagnostic MRI for management of their LBP. There was a notable increase in the number of patients requiring back or spine injections in the non-EBP group when compared to the EBP group with a percentage difference of 44% (Table 3). The significance of this isolated finding is unclear given the small sample size.

Other studies suggest that EBP may lead to the development of chronic LBP. A study by Martinez et al. demonstrates EBP may contribute to the development of LBP. This prospective observational study of obstetric patients demonstrated a low back pain prevalence of 22.9% amongst patients treated with EBP, compared to 3.5% amongst non-EBP patients (p < 0.0001).¹¹ However, this study is limited by the short follow up of 3 months which precludes the assessment of chronic LBP. Additionally, our previous pilot study suggested that PDPH treated with an EBP is associated with an increased prevalence of subsequent low back pain in parturients following labor analgesia. The EBP group was found to be more likely to have chronic LBP (percentage difference 20% [95% CI 6–33%], RR 2.6 [95% CI 1.3–5.2]) and also LBP < 6 (percentage difference 24% [95% CI 9%–37%], RR 2.3 [95% CI 1.3–4.1]) compared to non EBP group.⁷ This study also had limitations including the retrospective nature with a long follow up period from the time of the index procedure leading to the possibility of recall and attributional bias. Additionally, only the EBP group had a dural puncture and thus the increase in back pain in this study may be attributed to the dural puncture rather than the EBP. Furthermore, both of these studies evaluated the effects of EBP on an obstetric anesthesia population and may not correlate with the patients we are evaluating with this current pilot study. A possible explanation for the development of back pain after EBP may be related to the local inflammatory response to blood injected into the epidural space. There is a small amount of evidence to suggest that blood in the epidural space can promote scaring and fibrosis.^12,13 Whereas this was the impetus for this study, our findings do not support long term deleterious effects of the blood patch.

This pilot study has limitations inherent to a retrospective cohort study. The retrospective design creates the potential risk of recall and attributional bias given the long follow up period from the time of the procedures and our follow up for data collection. Additionally, given the small sample size used for this pilot study, definitive conclusions regarding LP leading to the development of back pain or the safety of EBP cannot be made.

Conclusions

This aim of this pilot study is to examine the association of chronic LBP in patients who experienced a PDPH following a lumbar puncture and were treated with an EBP. The results of this pilot study suggest that there is no increased risk for the development LBP in patients who develop PDPH and are treated with EBP over patients who had dural puncture but did not require EBP. Other observations noted in this study include the development of chronic LBP in both groups after dural puncture that is higher than what is reported in the general population. However, given recall bias and the limitations of this small pilot study, no definitive conclusion can be drawn from these observations. Further long-term prospective studies are needed to confirm the findings of this pilot study and to ascertain association and causality of LBP after lumbar puncture.