Transcutaneous electrical nerve stimulation (TENS) for pain control in women with primary dysmenorrhoea

Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To evaluate the efficacy and safety of TENS on the basis of its frequency and acupoints, in comparison with placebo, no treatment, and other medical treatments for primary dysmenorrhoea.

Background

Description of the condition

Dysmenorrhoea refers to the occurrence of pain in the lower abdominal region during menstruation (Dawood 2006). Dysmenorrhoea is usually classified into two categories: primary and secondary. Primary dysmenorrhoea occurs in the absence of an identifiable pathological condition. When the menstrual pain is associated with an organic pathology such as endometriosis, uterine myoma, or adenomyosis, it is defined as secondary dysmenorrhoea (Dawood 2006).

The pathophysiology of primary dysmenorrhoea is based on the increased secretion of prostaglandin, which in turn induces uterine contraction and reduces uterine blood flow (Dawood 2006). These uterine contractions and reduced uterine blood flow are known to induce pain in women with primary dysmenorrhoea (Dawood 2006).

Primary dysmenorrhoea is known to have a substantial negative impact on the woman’s quality of life (Iacovides 2014), school or work attendance, and social or physical activity (Burnett 2005; Wong 2011). However, most women do not seek medical care to control their dysmenorrhoea pain, which makes attempts to accurately estimate the prevalence of primary dysmenorrhoea difficult (Lefebvre 2005). Thus, the estimated prevalence of dysmenorrhoea has varied among studies. According to a Canadian study that included 1,546 women, 60% of women experienced moderate to severe primary dysmenorrhoea, 51% reported discomfort resulting from limited activities during primary dysmenorrhoea, and 17% reported absence from work or school because of primary dysmenorrhoea (Burnett 2005).

Description of the intervention

It is difficult to completely treat primary dysmenorrhoea. The most common method to relieve the pain in primary dysmenorrhoea is treatment with nonsteroidal anti‐inflammatory drugs (NSAIDs) (Marjoribanks 2015). However, some women cannot use this type of medication because of problems related to its side effects, or because of contraindications for its usage. For these women, transcutaneous electrical nerve stimulation (TENS), which is a non‐pharmacological technique, can be an alternative treatment option to control pain (Oladosu 2018).

TENS involves attaching electrodes to the surface of the skin and delivering electrical currents to the body via the electrodes (Johnson 2015). When applying TENS, appropriate electrode positioning is essential, and electrodes should be placed on healthy skin (Johnson 2014). TENS is usually performed at the site of pain.

TENS is an effective and safe treatment, so it has been widely used for various symptoms or diseases in the clinical field, including acute pain (Johnson 2015), chronic pain (Gibson 2019), chronic low back pain (Gadsby 2006), cancer‐related pain (Hurlow 2012), neuropathic pain (Gibson 2017), osteoarthritis (Rutjes 2009), and pain in labour (Dowswell 2009). In addition to its effectiveness and safety, TENS also offers the advantages of being simple and inexpensive (Johnson 2015).

The limited research evidence regarding the side effects of TENS indicates that most women can use TENS safely (Johnson 2014). However, the manufacturer has identified some conditions as contraindications to TENS, including cardiac pacemaker usage, pregnancy, and epilepsy, because these conditions may be influenced by the electrical currents from TENS (Johnson 2014).

TENS can be applied with several dosing options, which allow variations in intensity and stimulation frequency (Sluka 2013). Two TENS techniques are commonly employed in clinical practice: 1) high‐frequency TENS (also referred to as conventional TENS); and 2) low‐frequency TENS (also referred to as acupuncture‐like TENS) (Johnson 2014). High‐frequency TENS is characterized by the use of high‐frequency and low‐intensity currents, whereas low‐frequency TENS is characterized by the use of low‐frequency and high‐intensity currents (Johnson 2014). Clinically, “high frequency” usually signifies more than 50 hertz (Hz), while “low frequency” usually signifies less than 10 Hz (Sluka 2003).

How the intervention might work

It is not entirely clear how TENS induces pain relief, though there are several theories regarding its mechanism of action. The pain relief mechanism of TENS in primary dysmenorrhoea is thought to be based on: 1) the inhibition of the transmission of painful stimuli according to the “gate control theory” (Melzack 1965; Dowswell 2009); 2) the release of endogenous opioids (Parsa 2013); and 3) the reduced muscle ischaemia of the uterus as a result of increased blood flow (Parsa 2013).

According to a previous review, for most situations, high‐frequency TENS (i.e. conventional TENS) is the first method of choice, whereas low‐frequency TENS is a treatment option for women who do not respond to high‐frequency TENS (Johnson 2014). However, for women with altered skin sensitivity, pain from deep structures, and radiating, widespread, or multiple‐site pain, low‐frequency TENS may be considered before high‐frequency TENS (Johnson 2014).

Why it is important to do this review

This is a new protocol for a new Cochrane Review, which will replace the current published review on this topic (Proctor 2002). The published review had reported a concern that the conclusions may not be powered adequately due to the small number of studies and participants. The review included seven studies, which were all conducted in the USA or Sweden and were published before 2000. In the meantime, research has continued in this field throughout the world, and according to ClinicalTrials.gov, the top three regions where trials for TENS were performed were the USA, Europe, and East Asia. Thus, we considered it necessary to address some of the limitations of the published Cochrane Review by including all the studies performed globally since its publication. In addition, the effect of acupuncture on acupoints is better than that on pseudoacupoints (Dincer 2003). The application of TENS at acupoints increased analgesia according to a previous review (Vance 2014). Therefore, we think that evaluating the relevance of application sites of TENS is important for clinicians to treat primary dysmenorrhoea. Overall, not only extending the search strategy, we also plan to examine the effects of TENS by application sites, to add quality‐of‐life as an additional outcome measure, and to implement advanced methodologies such as the revised version of Cochrane's 'Risk of bias' tool (Higgins 2016) and a 'Summary of findings' table.

Objectives

To evaluate the efficacy and safety of TENS on the basis of its frequency and acupoints, in comparison with placebo, no treatment, and other medical treatments for primary dysmenorrhoea.

Methods

Criteria for considering studies for this review

Types of studies

We will include only randomized controlled trials (RCTs) with either parallel or cross‐over designs. We will exclude quasi‐experimental studies and observational studies.

Types of participants

We will include participants if they meet all of the following inclusion criteria.

Inclusion criteria

• Women of reproductive age (12 to 49 years)

• Women with either clinically diagnosed or self‐reported primary dysmenorrhoea (dysmenorrhoea without any pelvic pathology, such as pelvic inflammation, endometriosis, uterine myoma, or adenomyosis)

We will not include participants if they meet any of the following exclusion criteria.

Exclusion criteria

• Women with secondary dysmenorrhoea (dysmenorrhoea due to pelvic pathology, such as pelvic inflammation, endometriosis, uterine myoma, or adenomyosis)

Types of interventions

We will investigate the following interventions: high‐frequency TENS, defined as 50 to 120 hertz (Hz) delivered at a low intensity (Latthe 2011); and low‐frequency TENS, defined as one to four Hz delivered at a high intensity (Latthe 2011). Placebos will include a treatment group that received pills made of an inert substance, as well as a treatment group that was treated using a TENS device identical to that of the active treatment group, except that it was incapable of producing an electric current. Other medical treatments will include but not limited to ibuprofen and acetaminophen. Acupoints will include but not limited to Hegu (LI4) and Sanyinjiao (SP6) (Wu 2012). Pseudoacupoints will include sites that are known as nonacupoints but are adjacent to the acupoints.

Comparisons

• High‐frequency TENS compared with placebo or no treatment

• Low‐frequency TENS compared with placebo or no treatment

• High‐frequency TENS compared with low‐frequency TENS

• High‐frequency TENS compared with other medical treatment

• Low‐frequency TENS compared with other medical treatment

• High‐frequency TENS on acupoints compared with high‐frequency TENS on pseudoacupoints

• Low‐frequency TENS on acupoints compared with low‐frequency TENS on pseudoacupoints

Types of outcome measures

Primary outcomes

• Pain relief (measured by visual analogue scale (VAS) or any other validated scale)

• Adverse effects (measured by incidence)

Secondary outcomes

• Requirements for additional analgesics (measured as the proportion of women requiring additional analgesics)

• Limitation of daily activities (measured as the proportion of women reporting activity limitation)

• Absence from work or school (measured as the proportion of women reporting absences from work or school)

• Health‐related quality of life (measured by 36‐Item Short Form Survey (SF‐36) (Ware 2000), World Health Organization’s Quality of Life Instrument – Short Version (WHOQOL‐BREF) (Skevington 2004), or any other validated instruments)

Search methods for identification of studies

Electronic searches

We will search the following electronic databases, including three Chinese, one Japanese, and seven Korean databases. We will not apply any limitations on date or language.

• Gynaecology and Fertility Group’s Specialized Register of controlled trials; PROCITE platform, from inception to present (Appendix 1)

• CENTRAL via the Cochrane Register of Studies Online (CRSO); web platform, from inception to present (Appendix 2)

• MEDLINE; OVID platform, from 1946 to present (Appendix 3)

• Embase; OVID platform, from 1980 to present (Appendix 4)

• PsycINFO; OVID platform, from 1806 to present (Appendix 5)

• Allied and Complementary Medicine Database (AMED); OVID platform, from 1985 to present (Appendix 6)

• Cumulative Index to Nursing and Allied Health Literature (CINAHL); EBSCO platform, from 1961 to present (Appendix 7)

• KoreaMed; web platform, from inception to present (Appendix 8)

• Korean Studies Information Service System (KISS); web platform, from inception to present (Appendix 9)

• Korean Medical Database (KMbase); web platform, from inception to present (Appendix 10)

• National Digital Science Library (NDSL); web platform, from inception to present (Appendix 11)

• Korea Institute of Science and Technology Information (KISTI); web platform, from inception to present (Appendix 12)

• Korean Traditional Knowledge Portal; web platform, from inception to present (Appendix 13)

• Oriental Medicine Advanced Searching Integrated System (OASIS); web platform, from inception to present (Appendix 14)

• China National Knowledge Infrastructure (CNKI); web platform, from inception to present (Appendix 15)

• Wanfang; web platform, from inception to present (Appendix 16)

• Chongqing VIP Information (VIP); web platform, from inception to present (Appendix 17)

• Scholarly and Academic Information Navigator (CiNii); web platform, from inception to present (Appendix 18)

Searching other resources

To identify additional studies, we will perform handsearches of the reference lists of all relevant publications. We will also perform searches to identify ongoing clinical trials in ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). In addition, we will search conference proceedings and some grey literature to identify relevant studies.

Data collection and analysis

Selection of studies

To ensure transparency and consistency throughout this review, we will follow a standard operating procedure for the selection of studies, data extraction, and data management, in compliance with Cochrane standards (Higgins 2011).

Three review authors (HS, PKS, and LHJ) will screen the titles and abstracts of all retrieved studies and remove those that are clearly not relevant. We will obtain the full text of all potentially relevant studies. We will prepare a list of the excluded studies, with reasons for exclusion. Any disagreements will be resolved by discussion or by an independent author (SHS). When necessary, authors of the retrieved studies will be contacted for further information. We will include a PRISMA‐compliant study flow diagram in the full review.

Data extraction and management

Three review authors (HS, PKS, and LHJ) will independently extract data from the selected studies by using a data extraction form. A variety of information will be obtained from each study, including participant characteristics, interventions, outcomes, results, adverse events, conflicts of interest, and ethical approval. Any disagreements will be resolved by discussion or by an independent author (SHS). When necessary, the authors of the selected studies will be contacted for further information.

Assessment of risk of bias in included studies

We will assess the risk of bias for each study by using the revised version of Cochrane 'Risk of bias' (RoB) tool (Higgins 2016), to assess the following domains: bias arising from the randomization process, bias due to deviations from intended interventions, bias due to missing outcome data, bias in measurement of the outcome, and bias in selection of the reported result. We will judge each of the domains of bias as either "low risk of bias", "some concerns", or "high risk of bias". All disagreements will be resolved by discussion and all judgements will be fully described.

Measures of treatment effect

For continuous data, if all studies report outcomes on the same scale, we will calculate the mean difference (MD) between treatment groups. If studies report outcomes on different scales, we will calculate the standardized mean difference (SMD). For dichotomous data, we will calculate odds ratios (ORs) using the numbers of events in the control and intervention groups of each study. We will present 95% confidence intervals for all outcomes.

Unit of analysis issues

We will perform the analysis per woman randomized. If studies with a cross‐over design are included, we will include only the first‐phase data (data prior to cross‐over) where possible. However, if these data are not reported, we will document this in the full review.

Pain relief will be measured using the VAS (0 to 10 or 0 to 100) or a categorical scale. However, in the meta‐analysis we will only include those studies that have outcomes measured on the same scale. Thus, the meta‐analyses for studies reporting VAS (0 to 10 or 0 to 100) and those reporting categorical scales will be presented separately.

Dealing with missing data

We will specify all assumptions and statistical methods for dealing with missing data. We will analyze data on an intention‐to‐treat basis whenever possible. If missing or insufficient data are found, we will attempt to obtain such data by contacting the first or corresponding authors of the relevant studies. We will present the additional information provided by the study authors. Where possible, we will compute the missing standard deviations (SDs) in compliance with Cochrane standards (Higgins 2011).

Assessment of heterogeneity

We will consider whether the clinical and methodological characteristics of the included studies are sufficiently similar for meta‐analyses to provide a clinically meaningful summary. We will assess heterogeneity among the included studies by measuring the I² statistic. An I² value greater than 50% will be considered to indicate substantial heterogeneity (Higgins 2011).

Assessment of reporting biases

If sufficient studies are included in this review, we will use a funnel plot to assess the possibility of reporting biases. If funnel plot asymmetry is observed, we will attempt to explore the possible causes of this asymmetry.

Data synthesis

We will perform statistical analyses using Review Manager 5.3 (Review Manager 2014). Where sufficient data are available, we will combine data using a random‐effects model for the planned comparisons (see Types of interventions).

We will use a random‐effects model as the base‐case analysis, since the true effect size might differ among studies, depending on the participant groups and interventions. If meta‐analyses cannot be used, the results from the included clinical trials will be presented qualitatively.

Subgroup analysis and investigation of heterogeneity

Where sufficient data are available, we will conduct subgroup analyses to investigate the possible reasons for heterogeneity. Specific subgroups that will be analyzed include the types of placebo and treatment duration of TENS.

Sensitivity analysis

Where sufficient data are available, we will conduct sensitivity analyses to determine whether the conclusions are robust to decisions made during the review process. These analyses will consider whether the conclusions would have differed under the following scenarios:

• when eligibility has been restricted to studies without a high risk of bias (defined as studies not at high risk of bias in any domain);

• when a fixed‐effect model has been adopted.

We will compare and discuss these results in the final review.

Overall quality of the body of evidence: 'Summary of findings' table

We will prepare a 'Summary of findings' table using GRADEpro GDT and Cochrane methods (GRADEpro GDT 2015; Higgins 2011). This table will evaluate the overall quality of the evidence for the main review outcomes (i.e. pain relief and adverse effects) for the main point of comparison in this review (i.e. high‐frequency TENS versus placebo or no treatment). We will prepare additional 'Summary of findings' tables for the main review outcomes for the other comparisons (see Types of interventions). We will assess the quality of evidence using the GRADE criteria (i.e. risk of bias, consistency of effect, imprecision, indirectness, and publication bias). Three review authors (HS, PKS, and LHJ) will independently grade the quality of evidence (high, moderate, low, or very low) and will resolve any disagreements by discussion. We will document and justify our judgements about the quality of the evidence.

Appendices

Appendix 1. Gynaecology and Fertility Group’s Specialised Register search strategy

PROCITE platform

Search from inception to present

Keywords CONTAINS "dysmenorrhea" or "Dysmenorrhea‐Symptoms" or "dysmenorrhoea" or "pain‐dysmenorrhea" or Title CONTAINS "dysmenorrhea" or "Dysmenorrhea‐Symptoms" or "dysmenorrhoea" or "pain‐dysmenorrhea"

AND

Keywords CONTAINS "TENS" or "TENS study" or "electro‐acupuncture" or "electro‐magnetic" or "electroacupuncture" or "electrical activation" or "Transcutaneous Electric Nerve Stimulation" or Title CONTAINS "TENS" or "TENS study" or "electro‐acupuncture" or "electro‐magnetic" or "electroacupuncture" or "electrical activation" or "Transcutaneous Electric Nerve Stimulation"

Appendix 2. CENTRAL via Cochrane Register of Studies Online (CRSO) search strategy

Web platform

Search from inception to present

#1 MESH DESCRIPTOR Dysmenorrhea EXPLODE ALL TREES

#2 dysmenorrh*:TI,AB,KY

#3 (pain* adj5 menstrua*):TI,AB,KY

#4 (pain* adj5 period*):TI,AB,KY

#5 (cramp* adj5 period*):TI,AB,KY

#6 (cramp* adj5 menstrua*):TI,AB,KY

#7 (menstru* adj3 disorder*):TI,AB,KY

#8 #1 OR #2 OR #3 OR #4 OR #5 OR #6 OR #7

#9 MESH DESCRIPTOR Transcutaneous Electric Nerve Stimulation EXPLODE ALL TREES

#10 TENS:TI,AB,KY

#11 electrostimulat*:TI,AB,KY

#12 electrotherap*:TI,AB,KY

#13 (electric stimulat*):TI,AB,KY

#14 (nerve stimulat*):TI,AB,KY

#15 electroanalges*:TI,AB,KY

#16 (Transcutaneous electric ):TI,AB,KY

#17 #9 OR #10 OR #11 OR #12 OR #13 OR #14 OR #15 OR #16

#18 #8 AND #17

Appendix 3. MEDLINE search strategy

OVID platform

Search from 1946 to present

1 exp Menstruation disorders/ 2 Pelvic pain/ 3 (pelvic adj5 pain).tw. 4 Dysmenorrhea/ 5 dysmenorrh$.tw. 6 (painful adj5 menstrua$).tw. 7 (painful adj5 period$).tw. 8 menstrual disorder.tw. 9 or/1‐8 10 Transcutaneous electric nerve stimulation/ 11 TENS.tw. 12 electric stimulation therapy/ or electroacupuncture/ 13 electrostimulat$.tw. 14 electrotherap$.tw. 15 electric stimulat$.tw. 16 nerve stimulat$.tw. 17 electroanalges$.tw. 18 or/10‐17 ) 19 9 and 18 20 randomized controlled trial.pt. 21 controlled clinical trial.pt. 22 (randomized or randomised).ab. 23 placebo.ab. 24 drug therapy.fs. 25 randomly.ab. 26 trial.ab. 27 groups.ab. 28 or/20‐27 29 (animals not (humans and animals)).sh. 30 28 not 29 31 30 and 19

Appendix 4. Embase search strategy

OVID platform

Search from 1980 to present

1 exp Menstruation Disorder/ 2 Pelvis Pain Syndrome/ 3 Dysmenorrhea/ 4 menstru$ disorder$.tw 5 (pelvi$ adj5 pain).tw 6 (painful adj5 menstrua$).tw 7 (painful adj5 period$).tw 8 Dysmenorrh$.tw 9 or/1‐8 10 nerve stimulation/ or transcutaneous nerve stimulation/ 11 electrostimulation therapy/ 12 TENS.tw 13 electrostimulat$.tw 14 electrotherap$.tw 15 electric stimulat$.tw 16 nerve stimulat$.tw 17 electroanalges$.tw 18 or/10‐17 19 9 and 18 20 Clinical Trial/ 21 Randomized Controlled Trial/ 22 exp randomization/ 23 Single Blind Procedure/ 24 Double Blind Procedure/ 25 Crossover Procedure/ 26 Placebo/ 27 Randomi?ed controlled trial$.tw. 28 Rct.tw. 29 random allocation.tw. 30 randomly allocated.tw. 31 allocated randomly.tw. 32 (allocated adj2 random).tw. 33 Single blind$.tw. 34 Double blind$.tw. 35 ((treble or triple) adj blind$).tw. 36 placebo$.tw. 37 prospective study/ 38 or/20‐37 39 case study/ 40 case report.tw. 41 abstract report/ or letter/ 42 or/39‐41 43 38 not 42 44 43 and 19

Appendix 5. PsycINFO search strategy

OVID platform

Search from 1806 to present

1 exp DYSMENORRHEA/ 2 dysmenorrh$.tw. 3 (painful adj5 menstrua$).tw. 4 (pain* adj5 menstrua$).tw. 5 (menstru$ adj3 cramp$).tw. 6 1 or 2 or 3 or 4 or 5 7 exp Electrical Stimulation/ 8 TENS.tw. 9 electrostimulat$.tw. 10 electrotherap$.tw. 11 electric stimulat$.tw. 12 nerve stimulat$.tw. 13 electroanalges$.tw. 14 Transcutaneous electric.tw. 15 7 or 8 or 9 or 10 or 11 or 12 or 13 or 14 16 6 and 15

Appendix 6. AMED search strategy

OVID platform

Search from 1985 to present

1 exp Menstruation disorders/ 2(pelvic adj5 pain).tw. 3 Dysmenorrhea/ 4 dysmenorrh$.tw. 5 (painful adj5 menstrua$).tw. 6 (painful adj5 period$).tw. 7 menstrual disorder.tw. 8 or/1‐7 9 Transcutaneous electric nerve stimulation/ 10 TENS.tw. 11 electric stimulation therapy/ or electroacupuncture/ 12 electrostimulat$.tw. 13 electrotherap$.tw. 14 electric stimulat$.tw. 15 nerve stimulat$.tw. 16 electroanalges$.tw. 17 or/9‐16 19 8 and 17

Appendix 7. CINAHL search strategy

EBSCO platform

Search from 1961 to present

#	Query
S40	S16 AND S39
S39	S38 NOT S37
S38	S17 OR S18 OR S19 OR S20 OR S21 OR S22 OR S23 OR S24 OR S25 OR S26 OR S27 OR S28 OR S29 OR S30 OR S31
S37	S35 NOT S36
S36	MH (human)
S35	S32 OR S33 OR S34
S34	TI (animal model*)
S33	MH (animal studies)
S32	MH animals+
S31	AB (cluster W3 RCT)
S30	MH (crossover design) OR MH (comparative studies)
S29	AB (control W5 group)
S28	PT (randomized controlled trial)
S27	MH (placebos)
S26	MH (sample size) AND AB (assigned OR allocated OR control)
S25	TI (trial)
S24	AB (random*)
S23	TI (randomised OR randomized)
S22	MH cluster sample
S21	MH pretest‐posttest design
S20	MH random assignment
S19	MH single‐blind studies
S18	MH double‐blind studies
S17	MH randomized controlled trials
S16	S7 AND S15
S15	S8 OR S9 OR S10 OR S11 OR S12 OR S13 OR S14
S14	TX Transcutaneous Electric*
S13	TX nerve stimulat*
S12	TX electroanalges*
S11	TX electric stimulat*
S10	TX electrotherap*
S9	TX electrostimulat*
S8	(MM "Transcutaneous Electric Nerve Stimulation")
S7	S1 OR S2 OR S3 OR S4 OR S5 OR S6
S6	TX menstrua* N3 cramp*
S5	TX menstrua* N5 disorder*
S4	TX pain* N5 period*
S3	TX pain* N5 menstrua*
S2	TX dysmenorrh*
S1	(MM "Dysmenorrhea")

Appendix 8. KoreaMed search strategy

1 "transcutaneous electrical nerve stimulation" [ALL]

Appendix 9. KISS search strategy

1 전체=transcutaneous electrical nerve stimulation

Appendix 10. Kmbase search strategy

1 [ALL=transcutaneous electrical nerve stimulation]

Appendix 11. NDSL search strategy

1 BI:(transcutaneous electrical nerve stimulation) AND BI:(dysmenorrhea)

Appendix 12. KISTI search strategy

1 (BI:TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION) AND (BI:DYSMENORRHEA)

Appendix 13. Korean Traditional Knowledge Portal search strategy

1 transcutaneous electrical nerve stimulation | TENS

Appendix 14. OASIS search strategy

1 transcutaneous electrical nerve stimulation

Appendix 15. CNKI search strategy

1 Menstruation disorder

2 Menstrual disorder

3 Pelvic pain

4 Dysmenorrhea

5 痛经

6 性痛经

7 月经痛

8 经期腹痛

9 经痛

10 1 OR 2 OR 3 OR 4 OR 5 OR 6 OR 7 OR 8 OR 9

11 Transcutaneous Electric Nerve Stimulation

12 TENS

13 electric stimulation therapy

14 electroacupuncture

15 electrostimulation

16 electrotherapy

17 electric stimulation

18 nerve stimulation

19 electroanalgesia

20 经皮神经电刺激

21 11 OR 12 OR 13 OR 14 OR 15 OR 16 OR 17 OR 18 OR 19 OR 20

Appendix 16. Wanfang search strategy

1 “Menstruation disorder”

2 “Pelvic pain”

3 Dysmenorrhea

4 痛经

5 经痛

6 1 OR 2 OR 3 OR 4 OR 5

7 “transcutaneous electric nerve stimulation"

8 "transcutaneous electrical nerve stimulation"

9 TENS

10 经皮神经电刺激

11 7 OR 8 OR 9 OR 10

12 6 AND 11

Appendix 17. VIP search strategy

1 “Menstruation disorder”

2 “Pelvic pain”

3 Dysmenorrhea

4 痛经

5 经痛

6 1 OR 2 OR 3 OR 4 OR 5

7 “transcutaneous electric nerve stimulation"

8 "transcutaneous electrical nerve stimulation"

9 TENS

10 经皮神经电刺激

11 7 OR 8 OR 9 OR 10

12 6 AND 11

Appendix 18. CiNii search strategy

1 “Menstruation disorder”

2 “menstrual disorder”

3 “Pelvic pain”

4 Dysmenorrhea

5 dysmenorrh*

6 月経障害

7 月経困難症

8 月経痛

9 生理痛

10 1 OR 2 OR 3 OR 4 OR 5 OR 6 OR 7 OR 8 OR 9

11 “Transcutaneous Electric Nerve Stimulation”

12 “Transcutaneous Electrical Nerve Stimulation”

13 TENS

14 “Electric Stimulation Therapy” OR Electroacupuncture

15 electrostimulat*

16 electrotherap*

17 electroanalges*

18 経皮的電気刺激

19 経皮電気刺激

20 11 OR 12 OR 13 OR 14 OR 15 OR 16 OR 17 OR 18 OR 19

21 10 AND 20

Contributions of authors

HS and PKS equally contributed to the protocol (co‐first authors). All authors read and approved the final version.

Sources of support

Internal sources

• None, Other.

External sources

• None, Other.

Declarations of interest

This review was supported by the Traditional Korean Medicine R&D Program, funded by the Ministry of Health & Welfare through the Korea Health Industry Development Institute (KHIDI) (HB16C0018); grant paid to the institution of SH and HSS.  HSS has received consultancy fees from Pfizer and Amgen.

Notes

This is a protocol for a new review which will replace the current published review: Proctor M, Farquhar C, Stones W, He L, Zhu X, Brown J. Transcutaneous electrical nerve stimulation for primary dysmenorrhoea. Cochrane Database of Systematic Reviews 2002, Issue 1. Art. No.: CD002123. DOI: 10.1002/14651858.CD002123.

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