Treatment of Pain Using a Non-implanted Intra-vaginal Electrical Stimulation Device Compared to Sham Device in Chronic Pelvic Pain

Chronic pelvic pain (CPP) is a complex and devastating diagnosis, encompassing multiple different conditions. Many organ systems may be involved including musculoskeletal, neurologic, genitourinary, psychiatric or gastrointestinal systems. Furthermore, it can be associated with major insomnia, psychosexual trauma, and mood disorders resulting in challenging cases characterized by pain that is refractory to standard treatment modalities. In a study conducted by Mathias et al., one in seven women experience chronic pelvic pain. The economic burden can be substantial, with previous estimates of 2.8 billion dollars per year. (1) Dyspareunia is defined as recurrent or persistent pain associated with sexual intercourse and affects approximately 8-21% of women in the United States (19, 20). Understandably, women with dyspareunia often suffer a decline in sexual functioning. It may lead to decreased arousal, loss of libido, and anorgasmia. However, its impact extends beyond sexual functioning as it can affect a woman's reproductive health and overall sense of well-being. Previous estimates indicate that 88% of sexually active chronic pelvic pain patients report pain during or after intercourse (1).

Treatment of chronic pelvic is challenging due to a poor understanding of pain processing and physiology. Each patient's experience of pain is unique and may be any combination of visceral, neuropathic, or even somatic in etiology. Persistent pain despite aggressive treatment of organic etiologies may imply a psychogenic overlay. A comprehensive and integrative approach is ideal and may include physical therapy, medications, or cognitive behavioral therapy.

Pelvic floor physical therapy is an effective treatment. Pelvic floor rehabilitation addresses the pelvic floor dysfunction and may include manual therapy, transvaginal biofeedback and electrical stimulation. Reissing et al. performed a retrospective chart review and discovered that physical therapy, particularly internal manual techniques, is a successful technique in treating patients with vaginismus (5). Electrical stimulation (ES) to the pelvic floor is an effective treatment in vaginismus, vulvar vestibulitis, urinary urgency, and levator ani hypertonus (11-15). ES delivered specifically through a transcutaneous electrical nerve stimulator (TENS) unit results in notable benefit in pain and dyspareunia (8,12,21-23). Murina et al. conducted a randomized controlled trial comparing use of a vaginal probe delivering electrical stimulation to a sham device. In this study, they used a TENS unit to treat vestibulodynia using a protocol of 15 min of 10 Hz followed by 15 minutes of 50 Hz. These sessions were completed on a twice per week basis for 10 weeks. Pain scores, dyspareunia and overall sexual functioning were significantly improved in the active arm compared to placebo (8). Another study used a TENS unit to treat primary dysmenorrhea. In this protocol, the TENS unit was set to 100 Hz with 100ms pulse width for the first 8 hours of the menstrual cycle and then repeated for another menstrual cycle (9). A smaller study of 12 women used electrical stimulation biofeedback and gradual desensitization in the treatment of vaginismus. After treatment, all 12 women were able to have vaginal intercourse (13).

Electrical stimulation is used extensively for the treatment of various pain disorders. It is delivered through peripheral nerve stimulation, a TENS unit, or sacral neuromodulation using an implantable device. Electrical stimulation has three different programmable settings including the frequency, intensity and pulse duration. High frequency is considered as > 50 Hz whereas low frequency is < 10 Hz. The intensity, also known as the power, of the unit can be set to a sensory or motor threshold with any frequency (2).

There are several theories to explain the mechanism of action of electrical stimulation. TENS works by altering the ability to perceive pain signals. The gate theory is one proposed mechanism of action. Electrical stimulation of nerves via a specific dermatome results in a blocking or gating effect at the dorsal horn of the spinal cord. This inhibits the transmission of pain impulses to the upper nervous system. Also, low frequency stimulation of the dermatome can increase the level of endorphins, providing pain relief. (2) The sacral nerve roots 2-4 hold the autonomic and somatic innervation of the pelvic floor, bladder, and urethra. Therefore, stimulation of the sacral nerve roots 2-4 can provide a means to modulate impulses from the pelvic floor. Inhibition of afferent innervation from the pelvic floor or bladder is achieved with afferent activation of the sacral nerve roots using Interstim® or similar devices. In other words, stimulating the sacral nerve roots through neuromodulation has an inhibitory effect on pain pathways at the spinal cord level. (3) Treatment of chronic pelvic pain may include peripheral nerve stimulation via the posterior tibial nerve. This mixed nerve shares the same spinal origin as the innervation of the bladder and pelvic floor. Stimulation of the posterior tibial nerve travels retrograde to modulate the afferent input from the bladder or pelvic floor. (4) Therefore, it shares a similar mechanism of action to sacral neuromodulation but spares the patient the complications associated with surgical implantation of a device.