TENS in the Treatment of Primary Dysmenorrhea
Dysmenorrhea is the occurrence of painful uterine cramps during menses and is the most common of all gynecologic complaints. Dysmenorrhea is divided into primary and secondary forms. Primary dysmenorrhea has no known pelvic pathologic etiology. Whereas secondary dysmenorrhea is related to the presence of pelvic lesions secondary to organic disease such as endometriosis, salpingitis, PID (pelvic inflammatory disease), adhesions, etc.1
Characteristically, primary dysmenorrhea starts shortly after menarche. The pain lasts for 48-72 hours of menstruation and is most severe during the first or second day of the menstrual cycle. Reported prevalence rates are as high as 90 percent.2 It is the leading cause of absenteeism of women from work, school, and other activities.3,4 A recent study of young Hispanic adolescent females showed that menstrual pain was significantly associated with school absenteeism and decreased academic performance, sports participation, and socialization with peers.5
In fact, 42 million women in the United States suffer from painful menstrual symptoms. Of these, about 3.5 million are unable to function for one to two days each month because the condition is so severe. In an older study, the economic implications were clearly presented — dysmenorrhea accounted for 600 million lost work hours and $2 billion in lost productivity annually.6
Women with primary dysmenorrhea have increased production of endometrial prostaglandin, resulting in increased uterine tone and stronger, more frequent uterine contractions. Majority of prostaglandins are released during the first 48 hours of menstruation, thus explaining the timing and limitation of symptoms. Prostaglandins stimulate an increase in myometrial muscle tone and contractions, and release of vasopressin in uterine blood vessels which may result in ischemic pain and other associated symptoms.1
Survey of Treatment Approaches
Pharmacologic options for the treatment of dysmenorrhea have traditionally been nonsteroidal anti-inflammatory drugs (NSAIDs) or the oral contraceptive pill (OCP). Both of these act by reducing uterine muscle activity.6 However, about 10 percent of affected women do not respond to these measures. In addition, the side effect profile of these drugs may make them less desirable in certain candidates. In fact, pharmacologic treatments may not be indicated in females who may not be able to tolerate the side effects of anti-inflammatory agents (traditional NSAIDS or cyclooxygenase-2 inhibitors) or who may not wish to take the OCP for other reasons.
Non-drug treatments have included transcutaneous electrical nerve stimulation (TENS). Electrodes are placed on the skin and electric current applied at different pulse rates and intensities to stimulate these areas in efforts to provide pain relief. High frequency TENS (also referred to as conventional TENS) usually consists of pulses delivered at 50-120 Hz at a low intensity (see Figure 1). Low-frequency TENS (also referred to as acupuncture-like TENS), on the other hand, usually consists of pulses delivered at 1-4 Hz at high intensity and with long pulse width. (See Figure 2.)
In obstetrics and gynecology, TENS has been found to be effective in alleviating labor pain.7 TENS seems to work by altering the body’s ability to receive or perceive pain signals, rather than by having a direct effect on the uterine contractions.8
Pain relief with TENS is postulated as involving two possible mechanisms, the gate-control theory as proposed by Wall and Melzak in 1965,9 or endorphin-mediated pain relief.10 The “gate” to sensory input is present in the spinal cord, which is stimulated by activity in small-diameter nociceptive fibers and closed by activity in large-diameter fibers. Therefore, if electric stimulation is applied to a peripheral site, the large diameter fibers are activated first and thus inhibit the small nociceptive fiber input transmitted to higher centers. The “gating” effect is established at the dorsal horn level of the spinal cord thereby inhibiting the transmission of pain-related impulses.9 This mechanism is thought to be responsible for the action of high frequency TENS.
Other studies on TENS have shown the pain relief attributed to TENS is reversible with opioid antagonists, leading to postulations that it somehow stimulates endogenous endorphins.10 An increased release of endogenous endorphins, resulting in potent analgesic effects, has been demonstrated with electrical stimulation. Pain relief that is partially reversible by naloxone has been shown to occur in low frequency TENS.11 However, increased levels of endorphins are found in CSF with both high and low frequency TENS.11,12
Studies have indicated that the effectiveness of TENS varies with the pulse frequency. Results of such studies, conducted utilizing both low- and high-frequency TENS, are discussed in the following sections.
Low Frequency TENS
In an early study of TENS and dysmenorrhea by Neighbors, et al, low frequency TENS was found to be an effective treatment modality.13 They treated 10 women with acupuncture-like TENS and 10 women with a placebo pill. They found a statistically significant reduction in pain immediately for subjects treated with acupuncture-like TENS, with 7 experimental subjects receiving at least 50% relief of pain and only 1 control subject receiving the same amount of relief.13 A similar study by Lewers et al, with 21 women divided into two groups — acupuncture-like TENS vs. a placebo pill — found there was no statistically significant difference in pain relief among the two groups.14 Both groups showed an average 50% reduction in pain immediately post-treatment. However, all test subjects in the study were also involved in a different experiment involving electrical conductance at four auricular acupuncture points and this may have accounted for the the skewed results.14
Another study by Santiesteban, et al., allocated women into Low Frequency TENS vs. Placebo TENS. Treatment time was 30 minutes. Pain relief was assessed prior to treatment and immediately after treatment, at 4 hours, 24 hours and 30 days. They showed no difference between the experimental and the control group for pain relief.15,16
High Frequency TENS
A study by Mannheimer et al, randomized women to the following three groups. High frequency TENS, Low frequency TENS, and placebo TENS. Treatment for all groups was 30 minutes in duration and then discontinued until pain returned. Upon return of pain, the subjects could reinstitute TENS and a record of use was kept. Pain was rated immediately before and after use. There was no significant difference between the two types of TENS but the high frequency TENS achieved slightly more pain relief.15,17