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

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.

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.

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).

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.

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.

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).

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.

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.