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October 2003

By Lisa J. Allen, DPT

The foot and ankle are ideal locations to exploit the benefits of iontophoresis. The process can penetrate up to 3 cm deep, so most structures of the foot and ankle can be reached in this way.

I had not used this modality as much before specializing in foot and ankle physical therapy, not only because structures are within target range, but also because of the plethora of “-itis’s” that occur there, such as tendinitis, neuritis, bursitis, fasciitis, and synovitis. Practicing in this area has led me to discover what a powerful modality iontophoresis is. Now that I have been using it so much for several years, I have come to agree with Joseph Kahn who stated in Scully & Barnes’ Physical Therapy that iontophoresis is “probably the most underutilized, misunderstood, and underestimated modality.”¹

By locally delivering a variety of drugs through the skin, iontophoresis offers a means to help control pain and inflammation, improve scar quality, decrease the symptoms of Morton’s neuroma, decrease edema, and decrease calcification in Achilles tendinitis.

To review the basic chemistry of iontophoresis, ions in solution are passed through the intact skin by passage of DC electrical current between two electrodes. Negative ions are carried through the skin at the negative electrode (anode) as would positive ions be transmitted at the positive electrode (cathode). In order for a substance to be delivered via iontophoresis, it must be ionizable.

A SEARCH FOR ANSWERS

The positive results of iontophoresis on so many of my patients and the lack of available textbook information led me to conduct a literature search. I wondered about using dexamethasone sodium phosphate (dex), the common steroid injected into painful joints and tendons. Injecting steroid is known to cause soft tissue atrophy. Could dex be causing the same problems with this delivery method? Research has answered this question.^2-4 It is a safe and effective alternative to using a hypodermic syringe because it eliminates the typical corticosteroid tissue trauma and systemic effects of bolus injections. We commonly warn our patients against injection of a steroid because it can cause local tissue damage and atrophy to the tendons, ligaments, or fat pads present. This can lead to tendon or fascial rupture (Achilles, plantar fasciitis) or insufficient fat pad cushioning in places like the ball of the foot (neuroma). Based on animal research, this is not a problem with delivering steroids via iontophoresis.

Another problem with steroid injections is that enough drug is administered to result in systemic levels of the drug. When using iontophoresis, there is no detectable blood level of the drug. This is important to note when educating your patients on the treatment you are proposing as some of them have a healthy fear of steroids.

Iontophoresis with dex at a 4 mg/mL concentration (negative polarity) is a powerful agent to address any inflammation. The prime targets in the foot and ankle include plantar fasciitis, tendinitis, bursitis, neuritis, capsulitis, metatarsalgia, and Morton’s neuroma. Once patients discover how much relief they obtain from this relatively inexpensive modality ($10 per electrode pack), they start requesting that you try it on a myriad of aches and pains. Although it has been postulated that dex may decrease pain by affecting pain fibers themselves, treatment with dex is questionable if the pain is due to some other cause that is not inflammatory.

When using dex, the results are noticeable within hours of treatment and last for 30 to 48 hours after the session, with permanent decrease in baseline pain within the first one to three sessions. However, it may take additional sessions to completely resolve the issue. The biggest problem I encounter with stopping iontophoresis with dex is that patients get such relief they do not want you to stop including it in their physical therapy regimen. This problem may be resolved by asking the patients to skip one session and note the difference. Then the decision to continue or discontinue is clear.

Scar tissue can cause a greater problem on the foot than on non-weight-bearing parts of the body. Iontophoresis with sodium chloride (NaCl) may improve the quality and decrease the bulk of a scar. The theory behind using sodium chloride 0.9% on scar (negative polarity) is that the chloride ions interrupt collagen cross-linking. By massaging the scar before and after NaCl iontophoresis, I find that the patient reports more comfort and the feeling of a “softer” or more yielding scar after treatment. Scarring on the plantar surface of the foot can be so painful as to cause altered gait, limiting the patients’ functional mo-bility. Altered gait will ultimately affect other joints such as the hip, knee, back, or neck. Scars elsewhere on the foot can create problems with shoeing. Painful or thickened scars can limit the patient’s ability to don situation-appropriate footwear, or their ability to wear any type of shoe.

DIAGNOSIS-SPECIFIC PROTOCOLS

For plantar fasciitis, in addition to other classic physical therapy treatments such as ultrasound, stretching, and massage, use iontophoresis with dex at the painful point on the medial calcaneal tubercle or along the longitudinal arch. For those patients who are left with a painful plantar scar after surgical plantar fascial release, use NaCl iontophoresis directly over the scar and/or dex iontophoresis for the inflammation. The patient is often quite clear regarding which substance provides the most relief.

With neuritis or hypersensitivity, try to find a point where there is a positive Tinel’s sign. If you cannot, have the patient try to localize the area that is most painful and place a pad soaked with dex on that area. If you know where the nerve would most likely be entrapped, work on it there, especially if the symptoms are diffuse and pinning down a point as small as the treatment electrode is proving difficult. I use this in addition to other treatments such as nerve gliding and desensitization massage.

For Morton’s neuroma, place the electrode filled with dex on either the top or the bottom of the web space (most commonly between toes 3 and 4). The skin on the top of the foot is thinner and easier to transmit through, but it is more sensitive. The skin on the bottom of the foot is less sensitive to the sensation and side effects of iontophoresis, but the callous and fat pad may limit the drug penetration.

Tendinitis, bursitis, and synovitis are the easiest. Use dex and place the active electrode over the most painful area.

With calcific tendinitis and calcific deposits, if you have access to the x-rays of the area, it makes things very simple; you can see the area of calcification to target. If not, place the pad soaked with 0.25% acetic acid (negative polarity) in the most common area of calcification. Ionized acetic acid binds with calcium and allows it to dissolve into solution, thereby decreasing the amount of bony deposit.⁵

For scar tissue, use 0.9% sodium chloride (negative polarity) directly over the problem scar and follow with scar massage. I may also use dex for inflammation and hypersensitivity of a scar. Other tactics for scars include a long ultrasound and scar massage.

For pain, apply a treatment electrode filled with lidocaine (positive polarity) for temporary pain relief. If the pain is due to inflammation, you will get excellent pain relief with dex.

With edema, use of dex over an area that is swollen because of inflammation will impressively decrease the condition. Frequently but not always, the edema will come back, but it will be less than it was initially, similar to the response to retrograde massage, which I recommend performing before the iontophoresis so that the medicine is not pushed out of the area.

Dex works beautifully on both osteoarthritis and rheumatoid arthritis (RA) to decrease the inflammation, pain, and swelling of a joint. It works best if you know where there is a clear route to the joint. An example in the ankle would be the sinus tarsi. In hallux limitus, apply around the joint line. Even patients with RA who are on oral steroids find relief with the local application of dex via iontophoresis.

IONTO TIPS

Here are some tips to make iontophoresis work better for you:

If the patient complains of burning or itching, or treatment time is excessive:

Turn up the intensity gradually if someone is expressing discomfort. Initially increase intensity to a very comfortable tolerance. Go and do something else, then return. Turn it up several clicks at a time and give the patient a few seconds to minutes at that level before increasing again. Wait and repeat. This should have the patient completing their treatment within 15 minutes.
Place an ice pack loosely over the active and the return electrodes. The manufacturers of commercially available iontophoresis electrodes discourage this, so use this tip with caution. Do not compress the pad. If excessive pressure is applied in one spot, for instance right over the snap, the current will travel preferentially through that spot only and not the rest of the pad. This small area of concentrated current can cause a blister right at that spot.
Gently rub your finger all over the back of the active electrode to ensure good contact and thorough wetting of the electrode.
Increase the distance between the active and the dispersive electrodes.
Advise your patient not to shave the area on therapy days.
Remove the active electrode and add a little more medicine to the pad to ensure it is thoroughly wet.
Remove the dispersive and rub your finger, moistened with tap water or ultrasound gel, on the electrode surface before replacing.
Move the electrode to a less sensitive area.
If you have a small cut or opening in the skin beneath the electrode, move the pad to a new location. Electricity takes the path of least resistance and will travel through open or new skin more than intact, mature skin.

CARE CONSIDERATIONS

I like to complete the applied heat, ultrasound, massage, and exercise before iontophoresis rather than immediately afterward because the increased blood flow could decrease the effectiveness of the treatment by flushing the drug out of the area more quickly. By the same token, I believe this is a good reason to ice at the same time, since that decreases the blood flow. As mentioned previously, this should be done with care. I would caution to not overly associate the level of stinging with blistering. There is some correlation, but there are many times when the patient has had a poor tolerance with no skin trauma. Ascertain if the burning sensation is over the entire pad, or if it is pinpoint. Always check the skin if someone feels discomfort, but if it is pinpoint, you will more likely have a problem with blistering. Ensure uniform contact or block the area that is tingling with a tiny piece of tape or petroleum jelly. Often there is nothing there, but pinpoint histamine blisters may have formed. I explain to the patient that most people report no discomfort with these blisters, which resolve within hours. All but a few think they are well worth the relief of iontophoresis with dex.

As you use it in the future, you will find that iontophoresis truly is an inexpensive, underutilized, and underestimated modality. It has made the experience of rehabilitation less painful for my patients. When they walk out feeling better than when they came in, it improves compliance. Less pain also means healing faster. Lastly, what I hope you gain from using iontophoresis in your clinic is that your patients come back asking for more of “that magic.” I don’t know about you, but I love it when my patients tell me I have magic hands. N Lisa J. Allen, DPT, is chief physical therapist for the Limb Center at Georgetown University Hospital in Washington, DC.

REFERENCES

Kahn J. Physical agents. In: Scully RM, Barnes MR, eds. Physical Therapy. Philadelphia: JB Lippincott Company; 1989:876-900.
Stralka SW, Head PL, Mohr K. The clinical use of iontophoresis. Physical Therapy Products. March 1996:48-51.
Glass JM, Stephen RL, Jacobson SC. The quantity and distribution of radiolabeled dexamethasone delivered to tissue by iontophoresis. Int J Dermatol. 1980;19:519-525.
Hasson SH, Henderson GH, Daniels JC, Scheib DA. Exercise training and dexamethasone iontophoresis in rheumatoid arthritis. Physiotherapy Canada. 1991;43:11-29.
Ciccone CD. Does acetic acid iontophoresis accelerate the resorption of calcium deposits in calcific tendinitis of the shoulder? Phys Ther. 2003;83:68-74.

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October 2003