What factors impact the clinical outcome of magnetic resonance imaging–guided focused ultrasound thalamotomy for essential tremor?

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Magnetic resonance imaging–guided focused ultrasound (MRgFUS) is a novel and useful treatment for essential tremor (ET); however, the factors impacting treatment outcome are unknown. The authors conducted this study to determine the factors affecting the outcome of MRgFUS.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>From May 2016 through August 2017, 15 patients with ET were admitted to Ohnishi Neurological Center and treated with MRgFUS. To determine the factors impacting treatment outcome, the authors retrospectively studied correlations between the Clinical Rating Scale for Tremor (CRST) improvement rate and age, disease duration, baseline CRST score, skull density ratio (SDR), skull volume, maximum delivered energy, or maximum temperature.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>The mean CRST score was 18.5 ± 5.8 at baseline and 4.6 ± 5.7 at 1 year. The rate of improvement in the CRST score was 80% ± 22%. Younger age and lower baseline CRST score were correlated with a higher CRST improvement rate (p = 0.025 and 0.007, respectively). To obtain a CRST improvement rate ≥ 50%, a maximum temperature ≥ 55°C was necessary. There was no correlation between SDR and CRST improvement rate (p = 0.658). A lower SDR and higher skull volume required significantly higher maximum delivered energy (p = 0.014 and 0.016, respectively). A higher maximum temperature was associated with a significantly larger lesion volume (p = 0.026).</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Younger age and lower baseline CRST score were favorable outcome factors. It is important to assess predictive factors when applying MRgFUS.</jats:p></jats:sec>

Outcome and Complications of MR Guided Focused Ultrasound for Essential Tremor: A Systematic Review and Meta-Analysis

“…Some studies in literature have tried to correlate various treatment parameters with the clinical outcome. SDR was significantly associated with the outcome at 1 and 6 months by Sinai et al (41), while no such relationship was found in other studies (42,44,46). The study which included patients with SDR < 0.4 found no statistically significant difference in the mean SDR of patients who had sustained improvement in symptoms and those who had recurrence of symptoms in this study.…”

“…A recent case report mentioned 80 min as the sonication time (51). Four centers utilized a 1.5T MRI for the procedure (34,46,50,52) while the rest performed it on a 3T machine.…”

“…Intraoperative tremor reduction has not been found to correlate to outcome at 3 months, while procedure duration and number of sonications have been shown to be significantly less with the use of DTI (35). Studies have previously found an association between younger age, short disease duration, better baseline tremor scores, fewer number of sonications and a higher maximal temperature during treatment to a better outcome (35,44,46). Experience acquired with the technique has also been found to have a positive impact on the outcome positively (44).…”

Examining cognitive change in magnetic resonance-guided focused ultrasound capsulotomy for psychiatric illness

“…There is also likely a minimum lesion volume necessary to produce a clinical benefit. This balancing act is analogous to performing thalamotomies for essential tremor, where a lesion volume >170 mm 3 results in a greater incidence of adverse motor outcomes, but for lesions <170 mm 3 , the precise location is critical to mitigate the tremor 59,60 . Thus, a lesion must be large enough to result in a clinically beneficial disruption of the limbic circuitry but small enough to avoid cognitive sequelae.…”

Comparative evaluation of tractography-based direct targeting and atlas-based indirect targeting of the ventral intermediate (Vim) nucleus in MRgFUS thalamotomy

“…In addition to evaluating a larger number of cases, we compared direct coordinates, obtained by probabilistic single tract tractography mapping of the DRTT, and indirect atlas-based coordinates, using a "gold standard" targeting (i.e., the coordinates were we actually obtained clinically effective tremor reduction intraprocedurally). Moreover, the comparison using the amount of DRT tract included in the ablation lesion in our opinion could be little indicative of the matching with the indirect coordinates, since the diameter of the lesion (mean reported volume in literature, about 300–400mm 3 39 – 43 ) is much higher than the spatial resolution of the intra-procedural target shifts using MR guidance (0.1 mm). Moreover, the final lesion configuration and extent depend on many individual patient factors, the most relevant being, among others, the skull density ratio (SDR) values and the number of active transducers 29 , 38 .…”