A New Approach To Treating Painful Diabetic Neuropathy

      The use of musculoskeletal ultrasound provides podiatric practitioners with non-invasive diagnostic capabilities in the office setting. In addition, this diagnostic tool can also assist with interventional medical techniques for treating a number of pathologic conditions. One may also combine ultrasound with duplex imaging and color Doppler to provide a vascular assessment tool.       For this article, we will offer a closer look at the potential of combining musculoskeletal ultrasound with cryosurgery to treat tarsal tunnel syndrome. Before we discuss this new application via an intriguing case study, let us offer a quick review of the advances and evolution of cryotherapy and musculoskeletal ultrasound.       For more than 10 years, some podiatric professionals have been using non-invasive diagnostic ultrasound. The schools of podiatric medicine now teach musculoskeletal ultrasonography and have scanners in their radiology departments. This imaging modality enables one to diagnose and discover occult pathology in the musculoskeletal system.       In the beginning, clinicians mainly utilized this technology to image the plantar fascia and web space neuromas. Now podiatrists may utilize diagnostic ultrasound to diagnose most soft tissue pathology of the lower extremity. This includes tendons (tendonitis, tendon tears and ruptures), joint capsule and plantar plate tears, soft tissue masses (ganglions), stress fractures and more. In 1998, Wendelken, et. al., patented a method of imaging wounds using diagnostic ultrasound.1       Diagnostic ultrasound has many other uses in podiatry. Combining duplex imaging along with Doppler capability provides a non-invasive method to determine the status of the vascular system of the lower extremity. Color Doppler imaging of the venous system can reveal damage to the valves in veins. Duplex imaging may also show the presence of a thrombus within a vein, which is a potentially life-threatening condition. One may also use this same scanner to detect abnormalities in the arterial system. The measurement of velocities can reveal areas of stenosis within an artery, which, in turn, yield the percentage of closure.       Today, skilled podiatrists are now using ultrasound to assist in visualizing invasive treatments. Practitioners can use ultrasound for guidance as it allows for the visualization of trigger point injections. One can use this technique to inject into areas that are difficult to reach anatomically.       Ultrasound can also detect and locate foreign bodies. Skilled podiatrists can also perform needle-guided biopsies and guided aspirations using these same guidance techniques. One may also utilize ultrasound to guide plantar fasciotomies and assist in the sclerosing of web space neuromas (using 4% alcohol). These methods of using diagnostic ultrasound have advanced the podiatric profession through technology.

Understanding The Benefits Of Cryosurgery

      Cryosurgery is the application of extreme cold to destroy abnormal or diseased tissue. Clinicians use cryosurgery to treat a number of diseases and disorders. Physicians often treat skin lesions, including warts, skin tags, nevi and some skin cancers, with this modality. In podiatry, clinicians have utilized cryosurgery to treat skin lesions, including warts and skin tags, Morton’s neuroma and chronic plantar fasciitis.       Cryosurgery works by exposing cells to extreme low temperatures. The most common way of freezing cells is using liquid nitrogen as the cooling solution. There are a number of methods of using the liquid nitrogen including a spray, a cotton swab soaked with liquid nitrogen, and a cryoprobe. A number of articles in the literature explain in detail the construction and function of cryoprobes.2,3       Briefly, pressurized gas is released into a chamber within the probe. As the gas exapands, it causes a rapid decrease in temperature (as low as -70ºC). As a result of this decrease in temperature, the probe forms an ice ball on the tip measuring 3 mm to 10 mm in size. Depending on the intended use and application, one would directly expose the diseased or pathological tissue to the ice ball for a number of timed cycles (i.e., a two-minute freeze cycle and a subsequent 30-second thaw cycle).

How Combining Both Modalities May Benefit Patients

      Cryosurgery is a minimallly invasive procedure that clinicians are currently performing on peripheral nerves (web space neuromas). Podiatric physicians are also using this modality to treat heal pain caused by plantar fasciitis and the divisional branches of the nerves that innervate the heel.       When one performs this procedure properly, cryoneurolysis causes destruction of the nerve axion along with a breakdown of the myelin sheath. It is the intent of the procedure not to destroy all the nerve tissue but to preserve the structural components (the epineurium and perineurium). This perservation of the structural components allow for the regeneration of the axions.       One of the areas where peripherial nerves become entrapped is the tarsal tunnel. The patient with an entrapped nerve will experience pain and numbness due to the pressure placed on the posterior tibial nerve as it travels through the tarsal tunnel. Diagnostic ultrasound may be useful for non-invasive imaging of the tarsal tunnel and helping to identify the components that make up this anatomical area.

Case Study: A Patient With A Long History Of Neuropathy

      A 58 year-old Caucasian female with a history of non-insulin-dependent diabetes mellitus and peripheral neuropathy received a referral to our office. The patient complained of burning and shooting pain in the bottom of both feet for over the past 10 years.       The patient has been treated with various pain medications including Darvocet (Eli Lilly), gabapentin (Neurontin, Pfizer), duloxetine HCl (Cymbalta, Eli Lilly) and, most recently, pregabalin (Lyrica, Pfizer) 150 mg qhs. She has also been treated in pain management centers and had tarsal tunnel decompression surgery. The patient continues to complain of burning and shooting pain despite these medications and treatments. She describes the pain as a hot sensation in the plantar aspect of both feet and tingling, primarily in all the toes.       The patient’s past medical history is positive for non-insulin-dependent diabetes mellitus of 15 years, hypertension and osteoarthritis. Medications include Lyrica 150 mg qd, atorvastatin calcium (Lipitor, Pfizer), Centrum (Wyeth), conjugated estrogen tablets (Premarin, Wyeth) and metoprolol succinate (Toprol, AstraZeneca). The past surgical history is positive for inguinal hernia and total hysterectomy. She admits allergies to shellfish causing a skin rash and has no known drug allergies. Her social history and family history are noncontributory. A review of systems was most significant for her neuropathic burning pain in both feet.       Plain radiographs of both feet and ankles show no significant bony deformity fracture or bone tumor. The patient has excellent bone stock. We also obtained a MRI to rule out any evidence of a space occupying lesion. The MRI showed no soft tissue pathology in the tarsal tunnel region.       Upon the initial exam, the patient is alert and oriented. She is in no acute distress. The lower extremity exam shows her neurologic component to have decreased epicritic sensation to the plantar and dorsal feet, and a significant decrease in vibratory sensation to both feet. She has a negative Tinel’s sign in the tarsal tunnel bilaterally. Semmes Weinstein monofilament testing shows a complete absence of sensation to all areas tested on the plantar skin. Achilles and patella reflex are normal bilaterally and symmetrically. The patient has a negative Babinski response. The manual muscle power is normal for all muscle groups tested.       The vascular exam shows palpable pedal pulses, immediate capillary refill, superficial venous fill time (SVFT) within normal limits, no varicosities and normal distal cooling. Her dermatologic exam shows texture, turgor and temperature all within normal limits. She has no pedal lesions and no ulcerations. The orthopedic exam shows a pes planus foot type with gastrocsoleal equinus.       We performed our typical workup for this type of patient prior to considering cryosurgery of the posterior tibial nerve. This involves injection of 1 cc of 1% lidocaine directly into the posterior tibial nerve at the level of the ankle. If the patient has a significant decrease in symptoms, this suggests he or she would be a good candidate for cryosurgery of the posterior tibial nerve. This patient had 100 percent pain relief after a diagnostic nerve block of the posterior tibial nerve, which lasted for approximately five hours. We subsequently scheduled the patient for cryosurgery of the posterior tibial nerve, using diagnostic ultrasound to assist in exact placement of the cryosurgery probe.       We then followed up with the patient in one week, in one month and four months following surgery. She relates a 90 percent reduction in her painful diabetic neuropathy. She now does not need to take any of her previous medications for the diabetic neuropathic pain.

Combining Cryosurgery With Ultrasound: A Guide To Surgical Technique

      The procedure involves palpating the posterior tibial artery just proximal to the level of the medial malleolus. We begin by providing anesthesia using a 1 cc syringe of 1% lidocaine with 100,000 dilution of epinephrine. One would inject this solution subcutaneously with a tuberculin syringe 2.5 cm superior to the medial malleolus directly over the posterior tibial artery. We proceed to prep the area in the usual sterile manner with Betadine® and protect the area with a Sound-Seal® thin film dressing (BioVisual Technologies), an FDA-approved protective film dressing for diagnostic ultrasound exams.       Cover the area with the sterile dressing and mark the incision site using a sterile pen. A #11 sterile blade provides for a transverse 3 mm full-thickness skin incision. Take care not to violate any deeper structures. (In the aforementioned case study, we performed the procedure in the office under local anesthesia and without tourniquet assistance.) Using a blunt probe, gently penetrate the fascial tissue in the direction of the neurovascular bundle.       Use the diagnostic ultrasound machine carefully to help create a tunnel for the cryosurgery probe. Insert the probe into the incision site while under the guidance of the diagnostic ultrasound scanner. We use the HydroStep® Standoff pad to help facilitate compliance over bony prominences such as the medial malleolus. The standoff pad also moves vital structures into specific ultrasound focus zones. The combination of compliance and the shifting of structures deeper into focus zones provides better image quality and resolution.       Proceed to introduce the probe into the target area, namely the posterior tibial neurovascular bundle. Since the cryosurgery ice ball ranges in size of 3.5 to 10 mm, depending on environmental conditions, there is no need to dissect the nerve from its adjacent vein and artery.       After inserting the probe with pressure directly on the neurovascular bundle, the freezing technique begins. This involves a three-minute freeze cycle, which causes an ice ball formation around the neurovascular bundle. One can directly visualize this process in real time using diagnostic ultrasound imaging. After the initial three-minute freeze, perform a 30-second thaw cycle followed by a second three-minute freeze cycle and 30-second thaw cycle. Generally, the ice ball will surround most of the neurovascular bundle as one can see on the diagnostic ultrasound screen. Once this cycle is completed, withdraw the probe. Dress the incision site with a sterile antibiotic ointment and a gauze compression dressing. No sutures are needed.       Our general postoperative course involves no medications and no limitation of activity. The patient is able to shower the following day.

How Do Patients Fare Postoperatively?

      By no means does the aforementioned case study serve as a proven effective technique for treating peripheral neuropathy. The purpose of the case study and discussion is merely to enlighten the practitioner to the availability of new technologies, which may ultimately lead to improved patient care.       The combination of cryosurgery with musculoskeletal ultrasound guidance has resulted in 50 percent of the patients reporting an excellent result, which is defined as having 90 percent overall pain reduction. This still leaves 50 percent of our patients continuing with minimal to no change in their pain levels.       Initially, surgeons attempted this procedure by using a 25-gauge needle into the tarsal tunnel to locate the nerve through a patient’s response. A positive response from the patient was when he or she felt a shooting pain that traveled into the toe or heel. This technique resulted in a satisfaction rate of less than 50 percent. By incorporating diagnostic ultrasound guidance, thus ensuring exact placement of the probe, the results have been consistently higher at the 50 percent mark with several patients having 100 percent pain relief. They all continue with numbness as before but the burning hot pain resolves in over half the patients. The current patient population is 25 with the longest postoperative patient at four months.       This is an experimental procedure at this time but may prove to be a valuable treatment alternative for this debilitating condition in the future.

What About Cryosurgery For Tarsal Tunnel Syndrome?

      In regard to tarsal tunnel syndrome, cryosurgery has shown some promising results. However, outcomes are varied and at best reach about a 50 percent success rate.       There may be several factors affecting a consistent outcome with this procedure. Branching of the posterior tibial nerve may vary, thus resulting in freezing the nerve at the incorrect level after it has already branched. A second factor may be related to the freeze time of the nerve with a resulting incomplete destruction of the axon and myelin. There is a need to perform controlled studies on nerve tissue to determine the optimum freeze time. The third factor may be related to only partial freezing of the nerve itself. The posterior tibial nerve diameter can range from two to four times the diameter of the ice ball formed. Accordingly, there may be limitations in being able to freeze the entire diameter of such a large nerve.

In Conclusion

      Cryosurgery as a technology has been around for several decades. It is primarily used for malignant liver and prostate cancer. Recently, the use of cryosurgery has become more common in the podiatric community for foot and ankle nerve conditions (see “What About Cryosurgery For Tarsal Tunnel Syndrome?” below).       This technique, coupled with diagnostic ultrasound, provides an alternative to radical nerve decompression, which has significant recovery time and greatly varied outcomes. The procedure is not without risk, specifically total destruction of the nerve and the risk of tissue necrosis or the possible formation of an abscess. The guidance provided by ultrasound ensures proper placement of the probe and observation of the freezing process. Obviously, one must ensure the probe is not withdrawn until the thaw has occurred.       One may perform cryosurgery in the office with the patient under local anesthesia with minimal complications and no postoperative pain. The disability period is nonexistent and results at this time are satisfactory when one compares this technique to other, more invasive procedures. Patients who have exhausted all current treatment modalities and surgical procedures for diabetic neuropathy and/or tarsal tunnel syndrome without relief may want to consider this as another option.       Dr. Lambarski is affiliated with St. Mary’s Hospital in Amsterdam, N.Y. He is a Diplomate of the American College of Foot and Ankle Surgeons and is board certified by the American Board of Podiatric Surgery. Dr. Lambarski is a certified wound specialist and certified cryosurgeon.       Dr. Wendelken is affiliated with Calvary Hospital Center for Palliative Wound Care in New York City. He is an author, lecturer and consultant to companies on podiatric sonography. Dr. Wendelken has a number of patents involved with ultrasound and is a principal of BioVisual Technologies, LLC, in Westwood, N.J.
 

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