MedPharmRes
University of Medicine and Pharmacy at Ho Chi Minh City
Original Article

The analgesic tolerance to electroacupuncture in patients with chronic musculoskeletal pain: an observational pilot study

Phuong Minh Bui1https://orcid.org/0009-0002-4554-5410, Oanh Thi Kim Ngo1,2https://orcid.org/0000-0001-5729-153X, Thang Duc Pham1,*https://orcid.org/0000-0002-8197-8662
1Faculty of Traditional Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam
2Outpatient Department, University of Medical Center—Branch no. 3 at Ho Chi Minh City, Ho Chi Minh City, Vietnam
*Corresponding author: Thang Duc Pham. Faculty of Traditional Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam. E-mail: pdthang@ump.edu.vn

© Copyright 2024 MedPharmRes. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Sep 14, 2023; Revised: Jan 10, 2024; Accepted: Jan 11, 2024

Published Online: Jul 31, 2024

Abstract

Introduction:

Musculoskeletal disorders are one of the most common reasons for requesting home healthcare services in Vietnam. Multiple studies have demonstrated the effectiveness of electroacupuncture (EA) in treating chronic musculoskele-tal pain (CMP). This study aimed to provide preliminary insights into the development of analgesic tolerance to EA in pa-tients with CMP.

Methods:

This observational pilot study was conducted on 60 patients with CMP. All participants provided information re-garding their age, gender, origin, location of pain, duration of EA’s analgesic effect, changes in EA effectiveness over the course of treatment, concurrent therapies, and any adverse effects during randomly selected treatment sessions.

Results:

Among the patients with CMP, 51.6% reported that that the pain-relieving effect of EA lasted more than one hour post-treatment. The duration f this effect varied, lasting from over 12 hours to over 72 hours (90%). The majority of partici-pants (81.7%) noted that the effectiveness of EA either improved or remained stable throughout the treatment sessions. However, 18.3% of patients experienced a reduction in the analgesic effect of EA with the progression of treatment ses-sions.

Conclusions:

The pain-relieving effect of EA typically unfolds gradually and persists for a notable duration. Consistent and repeated EA treatment in patients with CMP could potentially lead to the development of analgesic tolerance.

Keywords: musculoskeletal pain; electroacupuncture; pain management

1. INTRODUCTION

Musculoskeletal disorders encompass a wide range of conditions affecting bones, joints, muscles, and connective tissues. These ail-ments can lead to pain and reduce functionality, ranking among the most debilitating health issues [1]. The cost associated with the management of chronic pain from musculoskeletal conditions represent a significant portion of healthcare expenditures [2]. In Vi-etnam, the most commonly sought-after home healthcare service was related to musculoskeletal disorders [3].

Several studies have showcased the effectiveness of electroacupuncture (EA) in treating chronic pain, particularly in various chronic musculoskeletal conditions [4,5]. In clinical settings, EA is widely used for chronic pain management, exerting its analgesic impact by activating the neuroendocrine system. The outcomes of EA are contingent upon the frequency used, with different frequencies trigger-ing the release of distinct endorphins [6]. Nevertheless, recurrent high-intensity EA could progressively diminish its analgesic effects [4–7]. Recent rat studies have indicated that repeated high-intensity sessions might lead to analgesic tolerance to EA [8,9].

Similarly, repeated use of therapeutic electrophysical agents that reduce pain through the release of endogenous opioids could grad-ually diminish their analgesic effect. Transcutaneous electrical nerve stimulation (TENS), a type of electrotherapy that alleviates chron-ic pain similarly to EA, has also been demonstrated to induce analgesic tolerance in patients following repeated application [10]. The aforementioned evidence suggests that consecutive EA treatment could potentially reduce its pain-relieving effectiveness. Therefore, this study aimed to observe the emergence of analgesic tolerance to EA in patients with musculoskeletal disorders.

2. MATERIALS AND METHODS

2.1. Study design and participants

This observational pilot study was conducted on 60 patients with chronic musculoskeletal pain (CMP). Participants were recruited from the University of Medical Center Ho Chi Minh City—Branch no. 3 (UMC—Branch no. 3). Data was collected from January 2023 to April 2023. The study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) state-ment. As this is the first research on EA tolerance in patients with CMP, we determined a sample size of 60 following the Central Limit Theorem [11].

The study included patients who met the following criteria: (1) aged 18 or older who provided their agreement to participate in the study; (2) diagnosed with chronic musculoskeletal disorders characterized by pain perceived in musculoskeletal tissues lasting or recur-ring for more than three months, accompanied by significant functional disability and emotional distress [12]; (3) treated with EA ac-cording to the standard treatment procedure at the UMC—Branch no. 3. Patients who did not comply with prescribed treatment were excluded.

2.2. Study setting

At the UMC—Branch no. 3, patients with CMP are typically treated with EA alone or in combination with nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, or herbal decoctions following the standard treatment procedure. Conventionally trained physicians perform the EA technique using the KWD808I EA Stimulator (manufactured by Changshansh, China), which em-ploys a continuous pulse pattern of 60 Hz for 20 minutes per session.

2.3. Data collection

An EA Multiple-Choice Questionnaire, adapted by the authors from the TENs Multiple-Choice Questionnaire by Johnson et al. [13] was used to evaluate the analgesic effects in patients undergoing EA treatment overtime. This questionnaire was administered through face-to-face interviews with each participant during randomly selected treatment sessions. It collected information on the pain’s origin, location, duration of EA analgesic effect, changes in the effectiveness of EA as treatment sessions progressed, concurrent therapies, and any adverse effects (Appendix 1).

2.4. Statistical analysis

Data was processed using Epidata 3.1 and analyzed with SPSS 20. Quantitative variables were presented as mean±SD due to nor-mal distribution, while qualitative variables were presented as frequencies. Statistical significance was considered at p<0.05.

3. RESULTS

3.1. Characteristics of participants

This study included a total of sixty eligible patients. These participants experienced an average of 12.3±8.37 EA sessions, and their characteristics, including age, gender, pain’s origin, location, adverse effects, and concurrent treatment, are presented in Table 1.

Table 1. Characteristics of participants
Value (%)
Age (years) 57.71±14.4
Number of EA sessions 12.3±8.37
Gender
Male 25 (41.7)
Female 35 (58.3)
Pain location
Neck 16 (26.7)
Back 32 (53.3)
Limbs 12 (20)
Pain origin
Osteoarthritis 33 (55.0)
Herniated disc 16 (26.67)
Trauma 3 (5.0)
Inflammation 4 (6.67)
Autoimmune disorders 1 (1.66)
Others 3 (5.0)
Concurrent treatment
Herbal decoctions 35 (58.3)
Acetaminophen and/or NSAIDs 1 (1.7)
Acetaminophen and/or NSAIDs with herbal decoctions 13 (21.7)
None 11 (18.3)
Adverse effects
Swelling 3 (3.3)
Skin irritation 1 (1.67)
Dizziness 1 (1.67)
Fatigue 1 (1.67)
Others 0 (0.0)

EA, electroacupuncture; NSAID, nonsteroidal anti-inflammatory drug.

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3.2. The analgesic tolerance to electroacupuncture (EA)

The majority of patients experiencing a pain-relieving effect from EA lasting more than one hour after the EA treatment. This effect was observed to lasts from over 12 hours up to more than 72 hours in 90% of cases. However, some participants (accounting for 18.3%) indicated a decrease in the effectiveness of EA as the treatment sessions progressed (Table 2).

Table 2. The analgesic effect of EA
Value (%)
Analgesic effect onset (hours)
0 9 (15.0)
0–0.5 10 (16.7)
0.5–1 10 (16.7)
1.0–2.0 5 (8.3)
>2 26 (43.3)
Duration of the analgesic effect (hours)
0–6 2 (3.4)
6–12 4 (6.7)
12–24 18 (30.0)
24–48 26 (43.3)
48–72 4 (6.7)
>72 6 (10.0)
Alterations in EA analgesic effect at random treatment sessions
Increase 30 (50.0)
Unchanged 19 (31.7)
Decrease 11 (18.3)

EA, electroacupuncture.

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4. DISCUSSION

4.1. Characteristics of participants

This study found a predominance female participants, align with findings from Jacobs et al. which also reported a higher prevalence of CMP among women in the Vietnamese population [14]. This gender difference may arise from various factors, including women’s tendency to communicate pain to healthcare providers and variations in biological factors (including hormonal and physiological aspects), pain tolerance, and psychological factors [15]. The mean age of individuals with CMP in our study was 57.71±14.40, con-sistent with observations by Parsons et al., who noted a higher prevalence of CMP in the age group between 50–60-year-old_group [16].

The majority of patients in this study reported pain originating from osteoarthritis and chronic back issues. This observation could be attributed to lumbar spine’s role in bearing weights in supporting the body [17]. Additionally, similar prevalence patterns of back pain predominance have been observed in several studies conducted in traditional medicine hospitals [18,19].

According to our findings, only five participants experienced adverse effects. Similar to a study by Patil et al., which reported that 2.2% of patients encountered adverse effects such as swelling, pain, fatigue, and depression [20]. This demonstrates the safety of EA therapy in treating CMP.

4.2. The analgesic tolerance to electroacupuncture (EA)

The results indicated that the onset of the analgesic effect often occurred more than one hour after the EA treatment. Price et al. re-ported that the analgesic effect of EA typically does not begin immediately but after 1 to 24 hours [21]. These findings suggest that the analgesic effect typically has a gradual onset, implying a neurohumoral mechanism of action. Previous studies have indicated in-creased endorphin and dynorphin levels in the cerebrospinal fluid following EA [22]. Some patients experienced immediate pain relief following EA treatment, which can be explained by Melzack and Wall’s gate control theory [23] or attributed to the cumulative effect of multiple EA sessions [24].

Regarding the duration of the pain-relieving effect, the research results showed that the analgesic effect of EA generally endured for a substential period. Previous research has demonstrated that this effect of EA can last from six hours to five days after a single session and even persist for six to twelve months after the completion of the treatment regimen [25,26]. The prolonged analgesic effect could be attributed to the cumulative impact of multiple EA sessions.

In this study, nearly 20% of participants reported a decrease in the pain-relieving effect of EA over time, which indicates the analge-sic tolerance to EA. A similar study by Johnson et al. on TENS effectiveness has shown that 32% of patients experienced a decline in TENS efficacy from the time with a median of four years [13]. This phenomenon has also been observed in animal study, where 100% of rats given EA for six consecutive days and in 100% of patients receiving five straight sessions of TENS [8–10]. Experimental studies in rats have suggested that prolonged, repeated EA stimulation can induce morphine tolerance, involving enzymes that degrad endoge-nous enkephalinases opioid peptides [22]. Moreover, the the release of endorphin induced by EA activates cholecystokinin octapep-tide, which might counteract the analgesic effects of these endogenous opioids [27]. These findings suggest that intermittent use of EA might avoid this phenomenon and restore treatment effects.

This study marks the first effort to investigate the onset, duration, and tolerance of EA analgesic effects in Vietnamese patients. This endeavor aims to establish a standardized treatment protocol, enhancing both cost-effectiveness and the degree of pain relief for pa-tients with CMP. However, our study does have limitations, including a limited sample size and the concurrent use of other therapeutic interventions alongside EA by participants. This situation could potentially make it difficult to avoid bias. With an observational design, it may be hard to manage confounding factors. Further research with a larger sample size and a randomized control trial design is needed to conduct a more accurate assessment of analgesic tolerance to EA.

5. CONCLUSION

The pain-relieving effect of EA tends to manifest gradually and endure for a significant duration. However, consistent and repeated EA treatment in patients with CMP may potentially lead to the development of analgesic tolerance. Further research is needed to un-derstand this phenomenon better.

Acknowledgements

We sincerely thank the University of Medical Center Ho Chi Minh City – Branch No. 3 for approval to perform this study. We would also like to express our deepest gratitude to the patients who agreed to participate and spend time throughout the study.

Funding sources

Not applicable.

Conflict of interest

No potential conflict of interest relevant to this article was reported.

Authors' contributions

Conceptualization: MP Bui.

Data curation: TD Pham.

Formal analysis: TD Pham.

Methodology: MP Bui.

Software: TD Pham.

Validation: OTK Ngo.

Investigation: MP Bui, OTK Ngo.

Writing - original draft: MP Bui.

Writing - review & editing: MP Bui, OTK Ngo, TD Pham.

Availability of data and material

Upon reasonable request, the datasets of this study can be available from the corresponding author.

Ethics Approval

All participants were comprehensively informed about the study’s particulars, which encompassed the procedures, and anticipated outcomes. The research adhered to the ethical principles outlined in the Helsinki Declaration and received endorsement from the Bio-medical Research Ethics Board at the University of Medicine and Pharmacy at Ho Chi Minh City (IRB-VN01002/IORG0008603/FWA00023448, dated 16 January 2023). All participants gave their written consent to participate in the study.

The identities of participants were maintained anonymously. Each patient was allocated a distinct study number, functioning as an identifier to distinguish individual data within the study cohort. Access to personal information was strictly confined to the authorized research team members under the lead investigator’s supervision.

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Appendices

Appendix
Appendix 1. Electroacupuncture multiple-choice questionnaire
Question Answer
Gender □ Female □ Male
Age (years)
Pain location □ Cervical □ Chest □ Back □ Limbs
Pain origin □ Inflammation □ Autoimmune disease
□ Osteoarthritis □ Trauma
□ Others □ Herniated disc
Number of EA sessions
Analgesic effect onset following EA (hours) □ 0 □ 0–0.5 □ 0.5–1
□ 1–2 □ >2
Duration of the EA analgesic effect (hours) □ 0–6 □ 6–12 □ 12–24
□ 24–48 □ 48–72 □ >72
Alterations in EA analgesic effect up to now □ Increase □ Unchanged □ Decrease
Concurrent treatment □ NSAID and/or acetaminophen
□ ‌NSAID and/or acetaminophen and herbal decoctions
□ None
Adverse effect □ Swelling □ Skin irritation □ Dizziness □ Fatigue
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