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ORIGINAL ARTICLE
Year : 2023 | Volume
: 26
| Issue : 1 | Page : 67-72
Ultrasound-Guided treatment of meralgia paresthetica: With or without corticosteroid? A double-blinded, randomized controlled study
Deniz Palamar1, Rana Terlemez1, Tugce Ozekli Misirlioglu1, Filiz Yıldız Aydın2, Kenan Akgun1
1 Department of Physical Medicine and Rehabilitation, Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty, Istanbul, Turkey
2 Department of Physical Medicine and Rehabilitation, Istanbul Bakirkoy Dr. Sadi Konuk Training and Research Hospital, Istanbul, Turkey
Correspondence Address:
Deniz Palamar
Department of Physical Medicine and Rehabilitation, Cerrahpasa Medical Faculty, Istanbul University-Cerrahpasa, Fatih, Istanbul
Turkey
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/aian.aian_883_22
Abstract
Background: Blockade of the lateral femoral cutaneous nerve (LFCN) with local anesthetic (LA) has therapeutic role as well as diagnostic value for meralgia paresthetica (MP). The aim of this study was to compare the effectiveness of ultrasound-guided LA and LA + CS injections in the treatment of MP. Methods: This was a prospective, double-blinded, randomized controlled study. Thirty-two patients were evaluated clinically, and electrophysiologically and diagnosed as MP by diagnostic block. They were randomly assigned to two groups and all patients completed the study. The first group (n = 17) received 2 mL of lidocaine 2%+1 mL of betamethasone, while the second group (n = 15) received 2 mL of lidocaine 2% + 1 mL saline solution. Results: No statistically significant difference was detected between the groups in numeric rating scale (NRS) values. In both groups, NRS values were significantly decreased after the injection that confirms the diagnosis of MP. The improvement continued on the following weeks in both groups. At the 4th week, the NRS value reached to 2.47 in the CS group and reached to 3.13 in the LA group. Conclusions: Both CS and LA injections for the treatment of MP were found to be clinically effective and both may be therapeutic options. In intractable cases, once the nerve block is applied with or without CS, well-being can be achieved by keeping the patient away from the triggering factors. To provide effective and isolated injection of LFCN, that may have frequent anatomical variations, ultrasonography guidance could be suggested.
Keywords: Corticosteroid, lateral femoral cutaneous nerve, local anesthetic, meralgia paresthetica, nerve block, ultrasound-guided
Introduction 
Meralgia paresthetica (MP), an entrapment of the lateral femoral cutaneous nerve (LFCN), presents with a localized area of pain, paresthesia, or numbness on the anterolateral region of the thigh. It can start spontaneously or iatrogenically as well, especially after conditions such as having surgery in the prone position.[1] Obesity, pregnancy, wearing of tight clothes, or masses located nearby the LFCN also may cause MP.[2] Bellinghausen and Marinelli reported meralgia paresthetica cases in COVID-19 patients after prolonged prone position in intensive care units.[3],[4]
The diagnosis of MP is usually based on the clinical findings with the presence of typical complaints in the typical area. Electrodiagnostic studies can be used to verify the diagnosis of MP.[5] Another technique that is accepted to confirm the MP is the diagnostic LA injections with or without CS.[6],[7],[8]
First-line treatment of MP is a conservative pharmacotherapy with nonsteroidal anti-inflammatory drugs and neuropathic pain agents; also, the regulation of activities of daily living and reduction of aggravating factors for avoiding likely causes of nerve compression, and recommending weight loss for obese patients. If the conservative regimen fails, then local injection of the LFCN, which may confirm the diagnosis through therapeutic success, should be performed.[1],[6],[7],[9],[10]
Blockade of the LFCN with local anesthetics (LA) has therapeutic role besides the diagnostic value. But commonly for the therapeutic purposes, local injection of the nerve is performed with the combination of LA and corticosteroids (CS).[1] The LFCN blocks could be done using anatomic landmarks, but due to the high anatomic variability of the nerve this landmark-based technique may cause false negative responses despite the use of large volumes of LA.[8] LFCN block could also be performed with imaging-guided techniques. Ultrasound-guided injection technique of LFCN has been published and proven to be safe.[11],[12],[13],[14] Also, ultrasonography has the superiority of showing the anatomic variability and morphologic changes of the nerve. In this study, we aimed to compare the effectiveness of ultrasound-guided LA and LA plus CS injections in the treatment of MP.
Patients—Methods Study design
A prospective, randomized, double-blinded, controlled trial was conducted in patients with complaints of pain, paresthesia, or numbness on the anterolateral region of the thigh in physical medicine and rehabilitation department of a university hospital. The Medical Ethics Committee of our university approved the trial, and all patients provided written informed consent prior to enrollment.
Study population
Thirty-one (n = 32) patients between the ages of 18 and 70, having unilateral pain, paresthesia, or numbness on the anterolateral region of the thigh, evaluated clinically and electrophysiologically and diagnosed as MP by diagnostic block, were included in this study, prospectively. The patients were warned not to do the triggering activities and aggravating factors from the moment they were referred for electrophysiological examination with the preliminary diagnosis of meralgia paresthetica. We included treatment-naive patients to this study, and during the follow-up period, we did not permit patients to start any medication such as anti-neuropathic pain agents. The exclusion criteria were having a neurological deficiency, a history of LFCN injection, a history of surgical procedures in the pelvic region, being pregnant or lactating, history of allergic reaction to the substance to be applied as LA, anticoagulant medication use, and history of inflammatory or infectious disease, active psychiatric disease, uncontrolled hypertension, uncontrolled diabetes mellitus, noncompensated chronic heart/liver/renal failure.
Baseline and control assessments were done by a physiatrist who was blinded to group allocation (RT). A detailed history including duration of complaints, aggravating factors, possible causative factors, history of trauma, history of weight gain, and medical history was obtained. Physical examination of the hip and lumbar spine was made to exclude other diagnosis. In neurologic examination, muscle strength, cutaneous sensation, deep tendon, and pathologic reflexes were assessed. Straight leg raise (SLR) test, Laseque test, and pelvic compression test were done. Leg lengths were measured to reveal if any leg length discrepancy present. Physical examination was done in order to find out any tenderness and Tinel sign around the anterior superior iliac spine (ASIS). After being clinically diagnosed as MP, electrodiagnostic study was performed to verify entrapment of the LFCN.
Patients were randomly assigned to two groups and all patients completed the study. The first group (CS group) (n = 17) received 2 mL of lidocaine 2% + 1 mL of betamethasone, while the second group (LA group) (n = 15) received 2 mL of lidocaine 2% + 1 mL saline solution. No medical treatment change was made during, or one month after the procedure.
Injection procedure
During the procedure, all the patients were placed in the supine position. LFCN was visualized, and all procedures were performed by using an ultrasonography device with a 7–13 MHz linear array transducer (LOGIQ P5, GE Healthcare, Little Chalfont, Buckinghamshire, UK).
The LFCNs were identified around the ASIS [Figure 1]. Sonographic palpation (local tenderness produced by pressure with the transducer “sono-palpation”) was done in order to find out any tenderness and Tinel sign where the nerve was visualized with ultrasonography. The procedure was performed with a 22-gauge needle, and using real-time ultrasound guidance and an in-plane technique by the same physiatrist (DP) in all patients who was experienced with ultrasound-guided interventions, under the supervision of the other experienced physician (KA) [Supplemental Video] [Additional file 1] . After the intervention, all the patients who were included in the study were warned about exacerbating activities such as wearing tight pants or tight belts.
Figure 1: Short-axis view of the lateral femoral cutaneous nerve (LFCN, white arrows). The LFCN appeared as a hypoechoic elliptical structure medial to the anterior superior iliac spine (ASIS)Outcome measurements
The primary outcome was pain intensity score assessed by numeric rating scale (NRS). In all patients, pain was assessed prior to the LFCN block, as well as post-injection, 2 weeks and 4 weeks following the injection procedure. The pain intensity score, as measured on a NRS, on which patient's rate their current pain intensity from 0 (”no pain”) to 10 (”worst possible pain”) was assessed by the same blinded physician who performed the initial clinical assessments. The response criteria included a NRS reduction of >50% after the procedure.
Intention-to-treat analysis
No dropout occurred while the study was being carried out, eliminating the need for an intention-to-treat analysis.
Randomization-sequence generation
The block randomization method was used for the randomization of the patients who were also blinded to group allocation. Same physiatrist (DP) generated the random allocation sequence, enrolled participants, and assigned participants to interventions.
Statistical analysis
Statistical analysis in this study was performed using the NCSS (Number Cruncher Statistical System) 2007 Statistical Software (Utah, USA) package program. Data are presented as mean ± SD, numbers, and percentage.
In the evaluation of the data, in addition to descriptive statistical methods (mean, standard deviation, median, interquartile range), the distribution of variables was examined with the Shapiro–Wilk normality test, in the comparison of the normally distributed variables the independent t test, the Friedman Test in the comparison of the time measurements of the variables that do not show normal distribution. Dunn's multiple comparison test was used for subgroup comparisons, Mann–Whitney U test for comparison of paired groups, Chi-square, and Fisher's reality tests for comparisons of qualitative data. A P value < 0.05 was considered statistically significant.
Results A total of 32 cases between the ages of 18 and 70 were enrolled and completed the study. The first group receiving CS consisted of 17 patients, while there were 15 patients in the LA group. The flow of patients in this study is presented in [Figure 2]. The demographic characteristics of the study participants were summarized as follows: In the CS group, the mean age of the patients was 53.29 ± 9.41 years and 52, 94% of them were female; in the LA group, the mean age was 50.60 ± 14.73 and 46, 66% of them were female. The body mass index (BMI) of the patients in the CS and LA group was 30.22 ± 5.55 and 28.89 ± 5.16, respectively. There was no significant difference in these demographic features between the groups [Table 1].
The average duration of pain in CS and in LA group was 26.06 ± 17.38 and 26.80 ± 44.11 weeks, respectively. The history of weight gain and duration of complaints were similar across the two groups [Table 2]. The other clinical parameters of the patients such as sense, pelvic compression test, leg length discrepancy, tenderness, Tinel sign, triggering with standing were examined, and there was no statistically significant difference found between the groups [Table 2].
The average baseline pain score was 6.24 ± 1.52 in the CS group and 6.07 ± 1.16 in the LA group, there was no significant difference (P = 0.875). In both groups, NRS values were significantly decreased one hour after the injection that confirmed the diagnosis of MP. The improvement continued on the following weeks in both groups. At the 4th week, the NRS value reached to 2.47 in the CS group and reached to 3.13 in the LA group [Table 3]. No statistically significant difference (P > 0.05) was detected between the groups in NRS score values. The course of the NRS values throughout the full 4-week follow-up period in each group is shown in [Figure 3].
Discussion Meralgia paresthetica is an entrapment neuropathy of LFCN, presenting as pain, numbness, and paresthesia along the anterolateral part of the thigh. Besides to electrodiagnostic studies, rapid and temporary relief of symptoms following LFCN block has been described as a specific diagnostic test for MP.[6],[7] In this study, we included cases with the diagnosis of MP by using nerve conduction study of the LFCN. Afterward, we confirmed the diagnosis with the injection test.
In this study, we aimed to investigate if there is an additional benefit of using CS for LFCN block in the management of MP. To our knowledge, this is the first study comparing the effectiveness of LA and CS injections in the treatment of MP. Our results show that LFCN blockage with 2 mL of lidocaine 0.2% with or without 1 mL betamethasone reduces the severity of the neuropathic complaints of MP. All patients had a positive response to the block without any adverse effect. We compared the pre-injection values with those of the post-injection NRS values, and significant improvements in all NRS measurements were observed in both groups after the procedure (P < 0.05). The improvement continued on the following weeks in both groups. At the 4th week, the NRS value reached to 2.47 in the CS group and reached to 3.13 in the LA group [Table 3]. No statistically significant difference (P > 0.05) was detected between the groups in NRS score values. Protection from causative and aggravating factors, the main components of the treatment, was applied in both groups. Once the pain blockade is applied with LA with or without CS, well-being can be achieved by keeping the patient away from the triggering factors.
LA and CS are the mostly used agents for blockage of the LFCN. LA injections may have therapeutic effects as well as being diagnostic tools.[15] In clinical practice, LA is commonly combined with CS. This practice is based on the expectation that the added CS may lengthen well response to the treatment. Although the effects of CS on the pain pathways are not completely understood, it is known that ectopic discharges in neurons may be suppressed.[16]
Lidocaine is one of the most commonly used local anesthetic agents. It selectively blocks A delta and C fibers. In addition to its local anesthetic properties, through blockage of sodium channels it can also cause vasodilation.[17] This mentioned effect of lidocaine can be managed with nitrous oxide (NO) that increases vascular microcirculation and reduces inflammation. Besides, through inhibition of nuclear factor—kappa B, lidocaine can cause anti-inflammatory effects.[18],[19] In our study, the reason behind lidocaine's therapeutic effects in LFCN injections could be the decrease in inflammation due to increase in microcirculation through NO.
Anatomical variations of the LFCN are not very rare. It can be seen in the quarter of patients and may be the explanation for negative response to blinded LFCN blocks.[8],[20],[21] We previously reported a LFCN variation that was visualized lateral to the ASIS with ultrasonography.[22]
The anatomical landmark-based method has high failure rates as low as 40%, secondary to the wide anatomic variability of the course of the LFCN.[23] The location of LFCN can be identified correctly with ultrasonography. In this study, we performed all injection procedures under the guidance of ultrasonography. All the patients had positive response to the injection under the ultrasonography guidance, and diagnosed as MP.
Meralgia paresthetica is commonly having a good response to the conservative treatment. First-line treatment includes medical agents, and avoiding activities enhancing nerve irritation.[10] When these treatment regimens fail, LFCN block should be done in intractable cases. There are several methods described in the literature for LFCN blocks. Blinded techniques can require repeated LFCN blocks for good response. Due to the frequent anatomic variations of the LFCN, imaging-based techniques should be preferred. Ultrasonography seems to be superior to the fluoroscopy and nerve stimulator techniques because this technique could show the course, and morphologic changes of the LFCN and additional lesions that may make compression to LFCN.[11],[13],[14],[24]
In a study, comparing US and blinded technique, Ng et al.[25] reported US, as a more reliable method than using bony landmarks to identify LFCN in both cadavers and volunteers. Hurdle et al.[11] reported that they have achieved 100% success although reducing the local anesthetic dose in blocks under the guidance of ultrasound. Reducing the dose of local anesthetic agent may decrease systemic and local adverse reactions, and also additional blocks of other nerves nearby, such as the femoral or obturator nerves, accidentally.[26]
The limitations of this study lie in the relatively small sample size, and the short duration of the follow-up period. With a follow-up period of four weeks, the long-term effects of the injections were not observed. Long-term efficacy of LA and also CS needs to be further confirmed with larger sample of patients.
In conclusion, both CS and LA injections for the treatment of MP were found to be clinically effective and both may be therapeutic options in cases resistant to conservative treatments. In intractable cases, once the nerve block is applied with or without CS, well-being can be achieved by keeping the patient away from the triggering factors. To provide effective and isolated injection of LFCN, that may have frequent anatomical variations, ultrasonography guidance could be suggested.
Compliance with ethical standards
Ethical approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.
Declaration of patient consent
Informed consent was obtained from all individual participants included in the study.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References 
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