CHAPTER 229 Transcutaneous Electrical Nerve Stimulation, Phonophoresis, and Iontophoresis
The procedures described in this chapter—transcutaneous electrical nerve stimulation (TENS), phonophoresis, and iontophoresis—can be performed either by primary care clinicians in their office or by physical therapists when ordered by a clinician. The procedures are often used with other physical therapy modalities such as manual therapy or therapeutic exercise. The choice of procedure depends on the size (localized vs. diffuse) and depth (superficial vs. deep) of the proposed treatment area as well as the specific pathologic process.
After discussing the patient’s diagnosis, the risks and benefits of the selected treatment should be explained, along with any treatment options. Oral or written consent should be obtained from the patient. Patients should be aware that their skin will be cleansed and that their hair may be trimmed. The anticipated treatment plan and total number of treatments should also be discussed.
Transcutaneous electrical nerve stimulation therapy uses low-voltage electrical pulses to stimulate the nervous system and is used for the treatment of pain syndromes. Skin surface electrodes are used to pass the electricity into the affected area. TENS units are Class II, U.S. Food and Drug Administration–approved devices and are typically selected for larger, generalized areas of pain, for chronic joint pains, or for persistent myalgias. This procedure can be performed in the clinician’s office and is reimbursable if performed by the clinician. However, TENS therapy is usually prescribed by a clinician and performed by the physical therapist. When prescribed for home use, the patient must be competent in operating a TENS unit.
TENS therapy is based on the gate theory of pain. According to this theory, nociperception (injury information) is transmitted through T cells that convey information to the higher brain centers. This information is presynaptically inhibited by interneurons in the substantia gelatinosa. TENS therapy bombards these interneurons, attempting to modulate or decrease the pain transmission by effectively blocking transmission of pain sensation. Other theories suggest that TENS therapy achieves its result by an acupuncture effect, by release of natural opiates, or by direct local vasodilation, which may reduce relative ischemia.
The goal of TENS therapy is to reduce or relieve pain and discomfort. This result may be either short lived or prolonged. TENS therapy may slowly break the pain–spasm–pain cycle and reduce perceived discomfort. Unfortunately, TENS therapy is not effective for pain of central origin (e.g., headache).
Phonophoresis uses therapeutic ultrasound to enhance the diffusion of medications across the skin and into body tissues. Commonly used medications include dexamethasone, hydrocortisone, and lidocaine. Although phonophoresis is usually performed by the physical therapist, some clinicians provide this modality in the office setting. Clinicians can be reimbursed for phonophoresis, even if not performed by a physical therapist.
The dual action of phonophoresis—thermal and mechanical—counteracts the inflammatory response by a process called acoustic streaming, which increases cell membrane permeability. This effect also facilitates the passage of medications into body tissue. With acute inflammation, using pulse-mode ultrasound avoids an increase in tissue temperature. In addition to the alteration of tissue permeability, beneficial effects are obtained through nonthermal changes (e.g., stimulation of fibroblasts). With chronic inflammation, using continuous or nonpulsed ultrasound can produce thermal changes that counteract or prevent the chronic changes of scarring and tissue edema.
Ultrasound dose is measured in intensity (intensity = W/cm2), which is the acoustic energy delivered through the surface area of the head of the transducer. Areas of inflammation are usually treated with 1 to 2 W/cm2 for 5 to 10 minutes. Results are measured by the improvement (either immediate or gradual) in pain or function of the treated area.