Introduction: Skull density ratio (SDR) is an important criterion for high-intensity focused ultrasound (HIFU) thalamotomy in essential tremor (ET) and tremor-dependent Parkinson’s disease (TDPD) patients. Bisphosphonates are postulated to raise SDR and improve HIFU outcomes through more efficient transmission of energy, but the impact of bisphosphonate pre-treatment on HIFU outcomes has not been described.
Methods: We retrospectively analyzed 222 patients who underwent HIFU thalamotomy between March 2022 and July 2024. All included patients had low SDR < 0.45, with some receiving preoperative bisphosphonates. Multiple statistical analyses were used.
Results: Forty-three patients met inclusion criteria. Eighteen patients (41.9%) used alendronate 70mg for an average of 129 days pre-surgery. Mean SDR was 0.409 for the bisphosphonate group and 0.413 for controls. No significant differences were found in lesion laterality, tremor etiology, or demographics between groups. The mean sonications were 6.5 for the bisphosphonate group and 7.2 for controls. Compared to controls, the bisphosphonate group had a mean last sonication energy of 21,610 versus 21,541 joules, duration of 23.9 versus 24.2 seconds, and maximum temperature of 52.5°C versus 53.3°C, with no significant differences found. Postoperative weakness occurred in 38.9% of the bisphosphonate group versus 12.0% of controls (p=0.04), while sensory abnormalities were 33.3% versus 68% (p=0.02), respectively. No significant differences were found in other postoperative neurological deficits. At initial follow-up, 100% of bisphosphonate patients and 92% of controls reported no tremor or mild tremor. By last follow-up, complete tremor resolution was seen in 77.8% of bisphosphonate patients against 92% of controls.
Conclusion : In our cohort, no significant differences were found in sonication energy, and bisphosphonate-treated patients exhibited higher rates of postoperative weakness but lower rates of sensory abnormalities. While further research is necessary, these initial results show few clinically significant differences in outcomes when using bisphosphonates for pre-treatment prior to HIFU thalamotomy in patients with low SDR.
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