Ultrasound-guided high frequency focused ultrasound neurolysis of peripheral nerves to treat spasticity and pain

Abstract

Spasticity, a complication of central nervous system disorders, signified by uncontrollable muscle contractions, is difficult to treat effectively. The use of ultrasound image-guided high-intensity focused ultrasound (HIFU) to target and suppress the function of the sciatic nerve of rabbits in vivo, as a possible treatment of spasticity and pain, will be presented. The image-guided HIFU device included a 3.2-MHz spherically-curved transducer and an intraoperative imaging probe. A focal intensity of 1480−1850 W/cm2 was effective in achieving complete conduction block in 100% of 22 nerves with HIFU treatment times of 36±14 s (mean±SD). Gross examination showed blanching of the nerve at the treatment site and lesion volumes of 2.8±1.4 cm3 encompassing the nerve. Histological examination indicated axonal demyelination and necrosis of Schwann cells as probable mechanisms of nerve block. Long-term studies showed that HIFU intensity of 1930 W/cm2, applied to 12 nerves for an average time of 10.5±4.9 s, enabled nerve blocks that remained for at least 7–14 days after HIFU treatment. Histological examination showed degeneration of axons distal to the HIFU treatment site. With accurate localization and targeting of peripheral nerves using ultrasound imaging, HIFU could become a promising tool for the suppression of spasticity and pain.