Stanley P. Leong, MD
Chief of Cutaneous Oncology, California Pacific Medical Center and Research Institute, Emeritus Professor of Surgery, University of California San Francisco
Worldwide incidence of melanoma is rising. Sentinel lymph node biopsy (SLNB) is indicated for patients with primary melanoma with T1b lesions and beyond  based on the recent classifications of the 8th edition of the American Joint Committee on Cancer (AJCC). The status of the SLN has been shown to be the strongest predictor of melanoma-specific survival by the MSLT-I. Although MSLT-II has shown again that SLN status is a strong predictor of melanoma-specific survival, the therapeutic benefit of completion lymph node dissection (CLND) has not been demonstrated. Thus, in patients with low tumor burden in the SLN(s), CLND may not be necessary. SLNB is a less morbid procedure with complication rate of about 5%  when compared with CLND of as high as over 50%.
Despite the fact that the complications such as lymphedema, pain, and nerve injury from SLNB are much less than those from CLND, major nerves are still exposed during SLNB for different nodal basins. Specific examples are: the spinal accessory nerve in the posterior triangle of the neck; thoracodorsal and long thoracic nerve in the axilla; ulnar, median, and radial nerves in the deep epitrochlear basin; femoral nerve in the groin; and sciatic nerve in the popliteal fossa. During lymph node dissection in these nodal basins, it is critical to identify and carefully preserve these nerves. Due to the more limited operative field in SLNB, the nerves may be more difficult to identify in these nodal basins. Whether undertaking a SLNB or CLND, it is imperative to identify and monitor the nerve so that it will be carefully preserved during dissection.
Due to its variable stimulation parameters, the Checkpoint Stimulator was proven to be an excellent tool to assist in localizing these nerves prior to visualization. The use of a charge-balanced, biphasic stimulation waveform allows safe continuous stimulation to tissue without causing any diminished muscle response or risk of nerve injury over time. The ability to repeat stimulation to confirm nerve function enables me to preserve the nerve throughout the procedure, which can be especially helpful during difficult dissections.
Demonstration of Usage
The linked videos provide a brief demonstration of my usage of the Checkpoint Stimulator in three recent lymph node dissections. The first case was an axillary lymph node dissection (Figure 1), showing the identification of the thoracodorsal nerve with the contraction of latissimus dorsi, and the long thoracic nerve with the contraction of the serratus anterior respectively. Initially, I used the 2.0 mA setting and swept across the tissue. When the stimulator probe was approximately 2-3mm from the nerve, a robust contraction of the muscle was observed. I then reduced the amplitude to 0.5 mA and pinpointed the nerve location. The device also employs a higher frequency setting of 16Hz, producing a tetanic contraction of muscle as opposed to a single twitch usually associated with nerve stimulation. I believe this nerve locating technique is not only safer, but reduces dissection time. In the second case (Figure 2), the femoral nerve was identified during an inguinofemoral lymph node dissection using the Checkpoint Stimulator, and confirmed by contraction of the quadriceps muscles. In the same way, I started with a higher amplitude setting of 2.0 mA approximating the nerve location to within several millimeters, then confirmed the location at the 0.5 mA setting. The third case demonstrates stimulation of the spinal accessory nerve in the posterior triangle of the left neck with contraction of the trapezius muscle (Figure 3).
In summary, for melanoma lymph node surgery either SLNB or lymph node dissection in the neck, axillary, epitrochlear, inguinal, and popliteal nodal basins, it is my practice that a Checkpoint Stimulator should be always available to confirm the appropriate nerve to avoid injury. In particular, during SLNB, as the operative field is relatively limited, the Checkpoint Stimulator will be of great benefit to identify and confirm the nerve. For the SLNB of the posterior neck and the popliteal fossa, it is critical to identify and confirm the spinal accessory nerve and the sciatic nerve respectively, as the consequence of cutting these nerves is disastrous.
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The Checkpoint Stimulator is a single-use, sterile device intended to provide electrical stimulation of exposed motor nerves or muscle tissue to locate and identify nerves and to test nerve and muscle excitability. Do not use the Checkpoint Stimulator when paralyzing anesthetic agents are in effect, as an absent or inconsistent response to stimulation may result in an inaccurate assessment of nerve and muscle function.
Please note: Case reports and white papers are company funded and not peer reviewed.