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Effect of caudal epidural steroid injection on electrodiagnostic parameters in patients with lumbosacral radiculopathy: A double-blinded randomized controlled trial
, Sushil Kumar Nayak2,, Narendra Bodhey3, Lakhiya Ravichandran4, Anusree Akshay4, Nirmalya Mohapatra5, Rabisankar Sahu6
*Corresponding author: Sushil Kumar Nayak, Department of Physical Medicine and Rehabilitation, Shri Jagannath Medical College and Hospital, Puri, Odisha, India. skn2050@gmail.com
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Received: ,
Accepted: ,
How to cite this article: Nandi J, Nayak SK, Bodhey N, Ravichandran L, Akshay A, Mohapatra N, et al. Effect of caudal epidural steroid injection on electrodiagnostic parameters in patients with lumbosacral radiculopathy: A double-blinded randomized controlled trial. J Neurosci Rural Pract. 2025:16:398-407. doi: 10.25259/JNRP_154_2025
Abstract
Objectives:
The aim is to compare the caudal epidural steroid injection (CESI) and caudal epidural normal saline injection (CENSI) injection in discogenic lumbosacral radiculopathy using nerve conduction study and subjective questionnaires-based outcome.
Materials and Methods:
Two postrandomized groups of lumbosacral radiculopathy patients (n = 40) were treated with either CESI (case group) or CENSI (control group), both under ultrasonography guidance. The outcomes were assessed at 2 weeks by electrophysiological parameters of lower-extremity nerves, namely, compound motor action potentials and F-wave parameters of common peroneal nerve and posterior tibial nerve. We also used subjective scales like the Oswestry low back pain disability index (OLBPDI) and the Numerical Rating Scale (NRS).
Results:
Delayed F-wave min latency was the single electrophysiological parameter that correlated well with established lumbosacral radiculopathy at the baseline. On subsequent evaluation after 2 weeks of epidural injection, both treatment groups were significantly effective in reducing pain and disability (OLBPDI and NRS). However, corticosteroid injection showed some evidence of electrophysiological superiority in comparing pre-post values of both lower-extremity nerves regarding amplitude, latency, and conduction velocity, but they were not statistically significant.
Conclusion:
The flushing effect of normal saline injected epidurally significantly improves the electrophysiological parameters of lumbosacral radiculopathy patients. Both clinical outcome and electrophysiological outcomes were comparable in both CESI (case) and CENSI (control) groups.
Keywords
Action potentials
Epidural
Low back pain
Radiculopathy
Saline solution
INTRODUCTION
Lumbosacral radiculopathy is one of the most important causes of chronic low back pain, having a significant contribution to disability burden of the working generation. Positive physical examinations typically show involvement of one or more lumbosacral nerve roots and are usually sufficient to make a diagnosis but lack objectivity. Electrodiagnostic studies play a significant role in establishing a diagnosis of radiculopathy. For example, Late Response (F wave and H reflex) latencies and compound motor action potential (CMAP) amplitudes of a few lower-extremity nerves have served to strengthen the diagnostic accuracy.[1]
Very few studies have tried to ascertain the difference between electrodiagnostic findings of lumbosacral radiculopathy patients in acute and subsequent quiescent stages, more so when the desired stage of relief has been achieved by an interventional approach like caudal epidural steroid injections (CESIs). In a significant recent study by Ibrahim et al. (2020) CESIs provide short-term improvement of symptoms in radiculopathy, which were well supported by electrodiagnostic parameters.[2] The injection effect had superiority to standard physical therapy in this regard still, the study did take into consideration the significant placebo effect and mechanical flushing effect of spinal interventions.[3]
The short-term efficacy of CESI in improving subjective pain parameters is now well established. Chou et al. (2015) conducted a systematic review and meta-analysis in patients with radiculopathy and spinal stenosis with epidural corticosteroid injections and found that immediate pain reduction was significantly higher than in the long-term period, and there was no effect on long-term surgery risk.[4] Similarly, Singh et al. (2018) concluded that following CESI in lumbosacral radiculopathy, there was a significant improvement in the Oswestry Disability Index and a decrease in the visual analog scale postinjection.[5]
Still, there is a paucity of studies that have tried to evaluate CESI on electrophysiological parameters. The tight dural sleeve and inflammatory or compressive injuries can cause more damage to the nerve roots than peripheral nerves. This might lead to demyelination, slowing of nerve conduction, and thereby significant changes in electrophysiological late responses.[6] For this reason, the H reflex or F-wave parameters can yield an objective assessment of the changing course of radiculopathies.
With this background, we envisaged our research plan including discogenic lumbosacral radiculopathy patients, where the control arm, i.e., caudal epidural normal saline injections (CENSI), will be provided with sham injections of normal saline, and the outcome will be assessed by the equivalent electrophysiological parameters. The outcomes were assessed by electrophysiological parameters of lower extremity nerves, namely, CMAP and F-wave parameters of common peroneal nerve (CPN) and posterior tibial nerve (PTN). Besides the primary outcome criteria of electrodiagnostic evaluation, we also used subjective back impairment scales such as the Oswestry low back pain disability index (OLBPDI) and the Numerical Rating Scale (NRS).[7,8]
MATERIALS AND METHODS
Ethics statement
The study was performed in adherence to the principles of the Declaration of Helsinki. The study’s protocol was reviewed and approved by the Institutional Ethical Committee. The patients who fulfilled the inclusion and exclusion criteria (which include magnetic resonance imaging [MRI]) were approached with the proposal of the study. The aim of the study was explained with a Patient Information Sheet, and Written Informed Consent was obtained from the participants.
Study design: A double-blinded randomized controlled trial
Inclusion criteria
Patients with lower back pain with unilateral or bilateral radiculopathy of a minimum of 1 month’s duration.
Physical examination should show nerve root irritation or abnormalities in neurological signs of the lower lumbar or upper sacral nerve root dermatomal distribution.
Adults (above 18 years) will be included.
Patients with MRI findings of disc protrusion or disc bulge at multiple levels of the lumbosacral spine show nerve impingement of lower lumbar or upper sacral roots with or without canal stenosis.
Exclusion criteria
Patients with severe psychiatric illness or any disease precluding prone positioning for the injection procedure
Patients with active infections or otherwise severely ill with any comorbid condition
Patients with neurological involvement that mandates immediate surgical interventions such as cauda equina symptoms or bladder or bowel incontinence
Patients having bleeding disorders and with a history of allergy to local anesthetics.
Sample size
Forty patients were enrolled in our study, with 20 patients in each treatment group. According to the literature, 17% in the saline group and 68% in the steroid group were expected to benefit at 4 weeks follow-up.[9] Considering the power of the study as 80% and the level of significance as 5%, the sample size calculation was as follows:
p1= 0.17, p2= 0.68
z1–α/2= 1.96, z1–β = 0.842
For a two-sided test:
n (sample size for each group) =
n = 16
Hence, we took 20 patients in each treatment group to account for unavoidable attrition, if any.
Data collection
A thorough history and physical examination were done as per the pro forma. The electrophysiological study (on Neurostim-NS 2 machine), OLBPDI, and NRS for pain were recorded. The parameters in the electrodiagnostic evaluation included the F wave, CMAP amplitude of the CPN, and PTN.
The randomization was performed to allocate the patients to the two treatment groups, i.e.
Caudal epidural corticosteroid injection CESI group: 1 mL of corticosteroid (40 mg triamcinolone) plus 19 mL of normal saline.
CENSI group: 20 mL 0.9% normal saline only.[10]
Randomization was done using the block method using the website randomisation.com. Patients were given serial-numbered envelopes containing cards indicating their treatment group, and the serial numbers were noted down. The investigator doing the initial screening, the investigator doing the procedures, and the investigator doing the outcome evaluation were different. Thus, both patients and investigators were blinded to the treatment received by an individual patient [Figure 1].
- Consolidated standards of reporting trials diagram. CESI: Caudal epidural steroid injection, CENSI: Caudal epidural normal saline injection.
At minor operation theater, the designated investigator received the envelope from the participant and carried out the procedure written inside it. The caudal epidural injection (both CESI and CENSI group) procedure was performed under the guidance of an Ultrasonography (USG) machine (Sonosite Edge II, Fujifilm Sonosite, Inc., United States) having a linear transducer with a frequency of 13-6 MHz and scan depth of 6 cm. Maintaining all the aseptic measures, the skin was infiltrated with 2 mL of local anesthesia, i.e., 2% lignocaine, and a spinal needle of 23G was inserted through the sacral hiatus [Figures 2 and 3] keeping an angle of 45°. The injectable material was pushed slowly under continuous USG guidance [Figure 4].
Follow-up of the per-protocol patients was typically done 2 weeks post-injection with the OLBPDI and the NRS and repeating the nerve conduction study (NCS).
- Relevant bony anatomy of sacral hiatus (Artwork by: Dr Jaydeep Nandi).
- Image showing a prone lying patient undergoing the procedure with all aseptic measures.
- Ultrasonographic image of needle (white arrow) approaching ligament of flavum (red arrow).
Statistical analysis
Data were coded, entered using Microsoft Excel software, and then imported into the Statistical Package for the Social Sciences (v. 18.0) for analysis. According to the type of data, the Chi-square test and paired t-test with the least significance difference were used to test differences for significance between pre- and post-assessments, and an independent samples t-test was used to determine the differences between the two treatment groups, i.e., CESI and CENSI. P-value was set at <0.05 for significant results.
RESULTS
The mean age for the CESI group (case) was 38.85 ± 8.92 years, and that for the CENSI group (control) was 41.15 ± 8.50 years. About 75% of the CESI group and 40% of the CENSI group were males. Besides age and sex, there was no statistically significant difference between the CESI group and the CENSI group regarding other parameters, namely, education, occupation, and MRI findings [Table 1].
| Baseline characteristics | CESI group (case) | CENSI group (control) |
|---|---|---|
| Age (mean age) | 38.85±8.92 years | 41.15±8.50 years |
| Gender | 75% (male) | 40% (male) |
| Education | 60% (higher secondary or more) | 15% (higher secondary or more) |
| Occupation (modified Kuppuswamy categories) | 10% (unemployed), 70% (skilled), 20% (professional) | 45% (unemployed), 50% (skilled), 5% (professional) |
| Marital status | 75% married | 100% married |
| MRI ligament of flavum hypertrophy | 15% (present) | 15% (present) |
| MRI presence of osteophytes | 75% (present) | 80% (present) |
| MRI-PIVD | L1–2 10% | L1–2 20% |
| L2–3 10% | L2–3 20% | |
| L3–4 30% | L3–4 45% | |
| L4–5 75% (5% extrusion) | L4–5 95% (5% extrusion) | |
| L5–S1 70% | L5–S1 75% | |
| 2 or more level PIVD 65% | 2 or more level PIVD 85% |
CESI: Caudal epidural steroid injection, CENSI: Caudal epidural normal saline injection, PIVD: Prolapsed intervertebral disc, MRI: Magnetic resonance imaging
On a paired t-test, statistically significant differences were observed between pre- and postintervention for OLBPDI in both groups (P <0.05; intra-group comparison). On intergroup comparison by independent samples t-test, we found that the CENSI group had more statistically significant OLBPDI improvement in contrast to the CESI group (P = 0.037). Although there was an intra-group improvement in both arms (paired t-test), the inter-group comparison for the NRS was not statistically significant (independent samples t-test). Hence, the CENSI group had more improvement than the CESI group on OLBPDI, and both were equally effective on the NRS [Table 2].
| Intra-group comparison of OLBPDI and NRS by paired t-test | |||
| CESI (case) (Mean± Standard deviation) | CENSI (control) (Mean± Standard deviation) | ||
| OLBPDI pre | 46.00±11.05 | 49.60±10.31 | |
| OLBPDI post | 26.10±10.96 | 24.10±7.88 | |
| P-value | 0.000** | 0.000** | |
| NRS pre | 7.40±0.94 | 7.35±0.88 | |
| NRS post | 3.20±1.32 | 3.15±0.99 | |
| P-value | 0.000** | 0.000** | |
| Inter-group comparison of OLBPDI and NRS by independent samples t-test | |||
| Patients | CESI (case) | CENSI (control) | P-value |
| Pre-value-post value (mean±SD) | Pre-value-post value (mean±SD) | ||
| OLBPDI change | 19.90±6.696 | 25.50±9.423 | 0.037* |
| NRS change | 4.20±1.005 | 4.20±1.196 | 1.000 |
The preintervention electrophysiological parameters of the CPN were recorded for both groups. 70% of patients in the CESI group (case) and 75% of patients in the CENSI group (control) had delayed F-wave minimum latency in the involved side of the lower limb, where the normal value was taken as 43.74 ± 4.28.[11] 55% of patients in both the CESI group and CENSI group had preintervention abnormal right-to-left difference of minimum latency, with 4 ms being taken as a cutoff for the foot.[12] Taking 6 ms as the cutoff for lower-extremity abnormal chronodispersion, almost no patients showed abnormal chronodispersion among the groups before intervention.[13] There were no statistically significant differences between the two groups in all the measured CPN electrophysiological parameters before the intervention procedure.
The preintervention electrophysiological parameters of the PTN were recorded for both groups. 80% of patients in the CESI group (case) and 70% of patients in the CENSI group (case) had delayed F-wave minimum latency in the involved lower limb. 45% of patients in the CESI group and 35% of patients in the CENSI group had an abnormal right-to-left difference of minimum latency. Furthermore, no patients showed abnormal chronodispersion among both groups before the intervention. There were no statistically significant differences between the two groups in all the measured PTN electrophysiological parameters before the intervention procedure [Table 3].
| Parameter | CESI (case) | CENSI (control) | P-value |
|---|---|---|---|
| Mean±SD | Mean±SD | ||
| CPN | |||
| CMAP | |||
| CPN latency | 3.30±1.21 | 3.13±0.95 | 0.624 |
| CPN amplitude | 16.92±12.4 | 20.02±13.81 | 0.46 |
| CPN conduction velocity | 47.20±6.00 | 50.39±7.26 | 0.137 |
| F wave | |||
| CPN min latency | 47.12±11.68 | 44.55±9.76 | 0.545 |
| Normal | 6 (30%) | 5 (25%) | 0.723 Chi-square test |
| Delayed | 14 (70%) | 15 (75%) | |
| CPN chronodispersion | 2.56±2.09 | 2.24±1.44 | 0.582 |
| Right-left difference of min latency (%) | |||
| Normal | 9 (45) | 9 (45) | 1.000 |
| Delayed | 11 (55) | 11 (55) | |
| PTN | |||
| CMAP | |||
| PTN latency | 4.65±1.47 | 4.64±2.86 | 0.149 |
| PTN amplitude | 18.57±12.98 | 25.86±15.08 | 0.270 |
| PTN conduction velocity | 50.02±7.40 | 52.31±7.28 | 0.158 |
| F wave | |||
| PTN min latency | 40.03±14.39 | 44.35±9.22 | 0.265 |
| Normal | 4 (20%) | 6 (30%) | 0.465 Chi-square test |
| Delayed | 16 (80%) | 14 (70%) | |
| PTN chronodispersion | 1.91±0.86 | 2.09±1.24 | 0.609 |
| Right-left difference of min latency (%) | |||
| Normal | 11 (55) | 13 (65) | 0.519 |
| Delayed | 9 (45) | 7 (35) | |
CPN: Common peroneal nerve, PTN: Posterior tibial nerve, CESI: Caudal epidural steroid injection, CENSI: Caudal epidural normal saline injection, CMAP: Compound motor action potential, SD: Standard deviation
We performed intra-group comparisons (i.e., pre- and postintervention) of the CESI group for both nerves. It showed postprocedure improvement in latency, amplitude, and conduction velocity (CV) of both nerves (not statistically significant). There was also an improvement in the mean value of F-wave minimum latency in both nerves (but significant in CPN only). Similarly, there was an overall improvement in the percentage of people having delayed F-wave minimum latency (but significant in PTN only). The abnormal right-left difference of minimum latency and chronodispersion did not show any significant trend in this corticosteroid group [Table 4].
| CESI (n=20) | |||
| CPN | |||
| Parameters | Pre-injection mean±SD | Postinjection mean±SD | P-value |
| CPN latency | 3.30±1.21 | 3.24±1.02 | 0.826 |
| CPN amplitude | 16.92±12.41 | 19.08±12.83 | 0.465 |
| CPN conduction velocity | 47.20±6.00 | 48.47±5.27 | 0.326 |
| F wave | |||
| CPN min latency | 47.12±11.53 | 41.56±12.29 | 0.011* |
| Normal | 6 (30%) | 10 (50%) | 0.197 Chi-square |
| Delayed | 14 (70%) | 10 (50%) | |
| CPN Chronodispersion | 2.56±2.07 | 2.54±1.72 | 0.957 |
| Right-left difference of min latency (%) | |||
| Normal | 9 (45) | 6 (30) | 0.327 |
| Delayed | 11 (55) | 14 (70) | |
| PTN | |||
| Parameters | Pre-injection mean±SD | Postinjection mean±SD | P-value |
| PTN latency | 4.65±1.47 | 4.03±0.98 | 0.149 |
| PTN amplitude | 18.57±12.98 | 15.87±13.77 | 0.270 |
| PTN conduction velocity | 50.02±7.40 | 53.66±9.88 | 0.158 |
| F wave | |||
| PTN min latency | 40.03±14.21 | 36.48±12.25 | 0.065 |
| Normal | 4 (20%) | 10 (50%) | 0.047* |
| Delayed | 16 (80%) | 10 (50%) | |
| PTN chronodispersion | 1.91±0.85 | 2.02±1.34 | 0.550 |
| Right-left difference of min latency (%) | |||
| Normal | 11 (55) | 11 (55) | 1.000 |
| Delayed | 9 (45) | 9 (45) | |
The same intra-group comparison was made for the CENSI group for both nerves. The studies showed postprocedure improvement in latency and CV of both the nerves (CPN and PTN) and mild deterioration in amplitude (not statistically significant). Furthermore, in the normal saline group, both nerves showed postprocedure significant improvement in F-wave minimum latency. Similarly, there was an overall improvement in the percentage of people having delayed F-wave minimum latencies (but significant in CPN only). Abnormal right-left difference and chronodispersion did not show any significant trend in the normal saline group [Table 5].
| CENSI (n=20) | |||
|---|---|---|---|
| Parameters | Pre-injection mean±SD | Postinjection mean±SD | P-value |
| CPN | |||
| CPN latency | 3.13±0.95 | 3.08±0.64 | 0.826 |
| CPN amplitude | 20.02±13.81 | 15.96±9.11 | 0.257 |
| CPN conduction velocity | 50.39±7.26 | 53.32±8.07 | 0.243 |
| F wave | |||
| CPN min latency | 44.55±9.63 | 39.11±12.65 | 0.000** |
| Normal | 5 (25%) | 12 (60%) | 0.025* Chi-square |
| Delayed | 15 (75%) | 8 (40%) | |
| CPN chronodispersion | 2.24±1.42 | 2.41±1.79 | 0.551 |
| Right-left difference of min latency (%) | |||
| Normal | 9 (45) | 10 (50) | 0.752 |
| Delayed | 11 (55) | 10 (50% | |
| PTN | |||
| PTN latency | 4.64±2.86 | 3.82±1.14 | 0.208 |
| PTN amplitude | 25.86±15.08 | 25.61±14.33 | 0.928 |
| PTN conduction velocity | 52.31±7.28 | 47.50±6.35 | 0.024 |
| F wave | |||
| PTN min latency | 44.35±09.10 | 32.82±12.44 | 0.000** |
| Normal | 6 (30%) | 10 (50%) | 0.197 |
| Delayed | 14 (70%) | 10 (50%) | |
| PTN chronodispersion | 2.09±1.22 | 2.05±1.29 | 0.861 |
| Right-left difference of min latency | |||
| Normal | 13 (65%) | 13 (65%) | 1.000 |
| Delayed | 7 (35%) | 7 (35%) | |
We analyzed the pre-post changes in electrodiagnostic values of the involved leg in both the treatment arms and both the nerves using the independent samples t-test. In the previous two tables, we compared the mean values of each parameter in pre- and post-settings, whereas in the next table [Table 6], the pre-post changes of each parameter were computed directly and compared between the two treatment groups.
| Parameters | CESI group (case) pre-post | CENSI group (control) pre-post | P-value |
|---|---|---|---|
| Mean±SD | Mean±SD | ||
| CPN | |||
| CPN latency | 0.06±1.12 | 0.05±1.14 | 0.987 |
| CPN amplitude | −2.16±12.94 | 4.06±15.53 | 0.177 |
| CPN conduction velocity | −1.27±5.64 | −2.93±10.88 | 0.548 |
| CPN min latency | 5.57±13.29 | 5.44±9.05 | 0.971 |
| CPN chronodispersion | 0.02±2.02 | 0.17±1.84 | 0.757 |
| PTN | |||
| PTN latency | 0.62±1.84 | 0.82±2.81 | 0.860 |
| PTN amplitude | 2.70±10.60 | 0.25±12.21 | 0.690 |
| PTN conduction velocity | −3.64±11.09 | 4.81±8.80 | 0.014* |
| PTN min latency | 3.57±12.07 | 6.53±9.31 | 0.995 |
| PTN chronodispersion | −0.11±1.13 | 0.04±1.27 | 0.446 |
In the late response study, the min latency of the F-wave showed improvement in both groups and nerves. Regarding chronodispersion, there was an improving trend in both groups in the CPN study, but only CESI failed to show improvement in PTN [Table 6].
DISCUSSION
The ultrasound-guided caudal epidural injection is a common office procedure for managing lumbosacral radiculopathy. Although there are multiple studies on its clinical efficacy, its neurophysiological impact is yet to be investigated well.
Clinical outcomes
In this study, both corticosteroid caudal epidural injection and normal saline placebo epidural injections were equally and significantly effective in reducing the NRS of the radiculopathy patients, which correlates with a significant placebo effect of the spinal injection procedure. On the other hand, normal saline injection was found to be better than the corticosteroid injection group on OLBPDI improvement among radiculopathy patients. The OLBPDI seems to be more effective in the assessment of chronic and more severely disabled persons, whereas our patients were all acute and had mild disability only.[14] Furthermore, the OLBPDI is more sensitive for patients showing significant improvement compared with patients having “unchanged status,” with only modest improvement in both the corticosteroid and saline group, leading to a lack of sensitivity of OLBPDI in our study.
Electro-physiological outcomes
Researchers did not have an encouraging response with late responses during the initial years. Aminoff et al., in 1985, evaluated unequivocal radiculopathy (L5 and/or S1) in 28 patients but reported a disappointing diagnostic yield of F-waves in only 5 patients with needle electromyographic (EMG) study.[15] However, recent studies depict the F-wave parameters showing similar or more sensitivity as compared to the use of needle EMG regarding L5/S1 radiculopathy. Weber and Albert studied patients with L5/S1 radiculopathy and reported needle EMG abnormalities in 70% and F-wave abnormalities in 69% of the patients. F-waves had the same sensitivity as needle EMG in the patients with weakness (approximately 90% in L5 and 80% in S1) and were more sensitive in the group of patients without weakness (L5 80%, S1 67%).[16] Toyokura and Murakami studied 95 patients with L5 and/or S1 root lesions (confirmed by surgery or myelogram) and found abnormal F-wave parameters in 70% of the patients and needle-electromyography abnormalities in 77%.[17]
In this respect, our findings correlate well with the findings of prior research available to us. Affected limb CPN and PTN NCS showed that more than 70% of people with radiculopathy had delayed F-wave latency (who were later divided into case versus control groups). Furthermore, more than 35% of people had an abnormal right-left difference of min latency in the beginning. However, there were almost no abnormal chronodispersions in patients with radiculopathy. Hence, “Delayed F wave latency” is the most consistent NCS change among clinically diagnosed lumbosacral radiculopathy patients, whereas abnormal Right-left difference of min latency is far less consistent in this respect.
Be it corticosteroid or normal saline, caudal epidural injections resulted in a positive electrophysiological response on postprocedure evaluation at 2 weeks. In both groups, there was postprocedure improvement in NCS parameters (amplitude, latency, CV) of the two lower-extremity motor nerves as well as improvement in F-wave minimum latency of the same two nerves. Although on evaluating all these four parameters (Amplitude, Latency, CV, and F-wave minimum latency) in Tables 4-6, improvement was more consistently found in the CESI group, considering only the improvement in F-wave minimum latency, the CENSI group is also an equivalent performer.
Overall, the findings suggest the possibility that the “flushing effect” of normal saline could have significantly improved the electrophysiological parameters of a radiculopathy patient, particularly the F-wave minimum latency. However, the abnormal right-left difference between min latency and chronodispersion did not show any significant trend in both groups.
Among the studies utilizing late responses as evaluation parameters, Toyokura et al. evaluated 30 patients with unilateral lumbosacral radiculopathy who were operated on for the herniated disc and showed significant (P < 0.05 in Wilcoxon signed-rank test) improvement in Peroneal F-min, F-max, F-difference, and tibial F-duration after surgery in all the patients with significant correlation with recovery of muscle weakness.[18] However, normalization of the F-wave was not always associated with full recovery in muscle weakness. These findings propose F-wave evaluation for postsurgical objective assessment.
Ibrahim et al. reported that the absence of F wave for the CPN was reduced among cases after the caudal epidural injection, without significant change in PTN parameters.[2] Moreover, only the injection group showed significant improvement in F-wave chronodispersion in both the CPN and PTN groups. In the control group, the corresponding changes were either insignificant or implied deterioration. Our findings had not been as straightforward, as we found that chronodispersion was inconclusive as an outcome criterion, even when we got clinical improvement. The mean F-wave minimum latency was significantly improved in both nerves and in both groups. The percentage of patients having a delayed F-wave minimum latency showed significant improvement in the PTN of the case group, but there was a similar significant improvement in both nerves of the control group. Findings of F-wave minimum latency implied that short-term electrophysiological improvement could be expected due to the flushing effect of normal saline (irrespective of corticosteroids being added or not).
Interestingly, there was some evidence for the electrophysiological superiority of corticosteroids in comparing pre-post values of CPN and PTN [Table 6], but that was not statistically significant. Overall, out of the total six values of amplitude, latency, and CV in two nerves, five showed improvements in the corticosteroid group, while only three showed improvements in the normal saline group.
Limitations
There are a few limitations to our study.
Multiple caudal epidural injections seem efficacious in many patients, which we did not incorporate into the protocol. For example, MacVicar et al. reviewed 39 publications and determined that 4% of individuals would require more than one injection to obtain a successful outcome.[19]
The study was not intended for the assessment of the long-term effect of the injection and only evaluated the outcome at 2 weeks after the intervention. The relatively small sample size is also a limitation of this study.
CONCLUSION
The patients treated either with corticosteroid caudal epidural injection or with normal saline placebo epidural injections were found to have significant and equivalent reductions in low back pain. The two electrophysiological parameters, delayed F-wave min latency and Abnormal R-L difference of min latency, were sensitive in lumbosacral radiculopathy patients at the onset, and there was an improvement in F-wave minimum latency in both case and control arms after treatment. Corticosteroid injection showed some evidence of electrophysiological superiority in comparing pre-post values of CPN and PTN regarding amplitude, latency, and CV without statistical significance. Finally, this study authenticates the incorporation of electrodiagnostic evaluation for lumbosacral radiculopathy prognosis irrespective of treatment options.
Ethical approval:
The research/study was approved by the Institutional Review Board at All India Institute of Medical Sciences, Raipur, Chhattisgarh, India, number AIIMSRPR/IEC/2021/704, dated April 09, 2021.
Declaration of patient consent:
The authors certify that they have obtained all appropriate patient consent.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.
Financial support and sponsorship: All India Institute of Medical Sciences, Raipur, Chhattisgarh, India, Sanction Order No. 22/41/2019/Admin/454 dated June 04, 2021.
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