TIP-29. Safety study of focused ultrasound neuromodulation for schwannomas and plexiform neurofibroma related pain

BACKGROUND Neurofibromatosis is a group of genetic disorders that can cause tumors including schwannomas and plexiform neurofibromas (PNs), often leading to chronic pain. Although there are two oral FDA approved drugs for PNs and one emerging for schwannomas, there remains a need for modalities that can manage pain effectively, limit systemic toxicity, and improve quality of life. Focused ultrasound (FUS) is an emerging therapeutic that uses acoustic energy to modulate nerve activity, with emerging analgesic applications. Here, we demonstrate its feasibility for neuropathic pain reduction and safety in schwannoma and PN patients. METHODS Five subjects with chronic pain from PNs or schwannomas received FUS to the nerve bundle proximal to the tumor. B-mode and displacement imaging were used to locate the nerve. Patients received 40 mechanical stimulations over the tumor using a solenoid impactor and rated their pain (1-10 scale). FUS (1.1 MHz, 5 MPa, 10s at 5% duty cycle) was randomly paired with half the stimulations in a double-blinded fashion. One of the subjects received FUS away from the nerve as an active control. RESULTS AND DISCUSSION A previous study conducted by our group employed this procedure in patients with peripheral neuropathies and found reduced pain (average 1-point reduction) in 4 out of 6 patients. Here, all tumor subjects treated on-target reported reduced pain with FUS (0.43-point decrease, p < 0.05 paired t-test). In addition to pain reductions, two patients relayed a “cooling sensation” and “loosening” in previously tense limbs. The control subject who received FUS away from the nerve did not report pain decreases. All patients tolerated the procedure well with no adverse reactions. This demonstrates the feasibility of FUS as a non-invasive approach for reducing tumor-associated nerve pain. Repeated FUS treatments will be examined next to define optimal procedures for robust pain reduction and improved functional outcomes.