Dec. 20, 2024
Surgical approaches for the treatment of tremor include focused ultrasound thalamotomy and deep brain stimulation (DBS). Whenever possible, Mayo Clinic specialists accommodate patients' preferences.
"Our multidisciplinary team evaluates patients with essential tremor to see if they would do better with ultrasound or DBS. If patients are great candidates for both, we personalize the therapy to what they and their referring neurologists prefer," says Rushna P. Ali, M.D., a neurosurgeon at Mayo Clinic in Rochester, Minnesota.
Mayo Clinic's neurosurgeons have experience with both approaches. "Effective execution of these procedures requires a large, multidisciplinary team of specialized neurologists, neurosurgeons and neuroradiologists," Dr. Ali says.
Advanced imaging for tremor treatment
Diffusion-weighted imaging shows a typical lesion in the left ventral intermediate (VIM) nucleus immediately after focused ultrasound treatment for essential tremor. Mayo Clinic neuroradiologists use diffusion tensor imaging (DTI) data to perform DTI tractography, to precisely localize the VIM target.
Expert MRI guidance is key. Mayo Clinic's neuroradiologists use diffusion tensor imaging (DTI) tractography. That noninvasive technique generates 3D, personalized white matter maps.
"A lot of practices use atlas-based measurements. But that approach doesn't allow us to see the nuclei directly," says Timothy J. Kaufmann, M.D., M.S., a neuroradiologist at Mayo Clinic's campus in Minnesota. "DTI tractography allows neuroradiologists to judge what neurosurgeons should target and what they should avoid, for maximum efficacy and minimal adverse effects."
The outcomes of these surgical approaches can be striking. "In appropriately selected patients, we're seeing over 80% improvement in tremors right after focused ultrasound therapy. Long-term data have demonstrated that these outcomes are sustained to at least the five-year mark," Dr. Ali says.
DBS treatment for tremor is offered at all three of Mayo Clinic's main campuses. "The outcomes are outstanding," says Kendall H. Lee, M.D., Ph.D., a neurosurgeon at Mayo Clinic's campus in Minnesota. "Essential tremor is sometimes called 'benign essential tremor.' But there's nothing benign about it. There's nothing essential about it. Patients are so happy when their tremor is gone."
Outlining the options
Besides neurologists and neurosurgeons, the team evaluating patients for tremor treatment includes physical and occupational therapists. Neuropsychiatrists provide input if anxiety or depression is a concern.
"Each specialist on the team looks at the patient through a certain lens," Dr. Ali says. "We want to represent all those domains and evaluate the patient as a whole, to a make sure we aren't missing any contraindications for therapy."
DBS involves implanting a thin electrical probe into the thalamus. A wire connects the probe to a neurostimulator implanted in the chest. The neurostimulator transmits electrical pulses to the thalamus to interrupt signals that might cause tremors. Contraindications include issues related to hardware implantation — such as multiple ongoing infections — as well as uncontrolled diabetes and increased risk of hemorrhage.
"Essential tremor is sometimes called benign essential tremor. But there's nothing benign about it. There's nothing essential about it. Patients are so happy when their tremor is gone."
Focused ultrasound thalamotomy is a noninvasive surgery in which focused sound waves travel through the skull. The waves generate heat to ablate tissue in a specific area of the thalamus to stop tremor.
Focused ultrasound is contraindicated in patients with skull density above or below certain thresholds, impaired gait, or speech dysarthria. "The two main issues we've noticed with focused ultrasound are worsening gait and speech after treatment. Patients who already experience those issues better fit the criteria for DBS," Dr. Ali says.
At Mayo Clinic, candidates for focused ultrasound are screened for neuropathy. In a study published in Tremor and Other Hyperkinetic Movements, Mayo Clinic researchers found that individuals with a history of neuropathy are likelier to experience gait decline after focused ultrasound therapy compared with patients without neuropathy.
Obesity and claustrophobia are additional contraindications, as focused ultrasound requires patients to spend several hours in a scanner. "Weight is modifiable. Patients who lose weight or have bariatric surgery can certainly have focused ultrasound when they meet the weight threshold," Dr. Ali says.
Focused ultrasound is initially performed only on one side of the brain. "We subsequently can offer a second-sided treatment, to control both hands, if patients have done well with the first side," Dr. Ali says.
Game-changing technology
Suboptimal targeting in tremor surgery might result in permanent deficits in sensory perception and motor weakness. "DTI tractography avoids those potential adverse effects to a very large degree," Dr. Kaufmann says.
Only a minority of centers use DTI tractography to guide focused ultrasound, and very few use it with DBS. The technology tailors treatment to patients' individual anatomies. "There's just enough variability in the shape and size of the thalamus — even variability from the left side to the right side within the same patient — that I can't imagine using a one-size-fits-all approach rather than direct patient targeting," Dr. Kaufmann says.
DTI tractography also avoids the need for microelectrode recordings, which must be performed while the patient is awake. That means patients who are reluctant to have awake surgery can have general anesthesia during tremor treatment. "DTI is an absolute game-changer," Dr. Lee says.
DBS typically requires the use of a headframe. But Mayo Clinic researchers developed a compact device platform that mounts to curvilinear bone and supports the attachment of surgical instruments. As described in the Journal of Neural Engineering, the system improves a patient's experience without compromising surgical accuracy.
Researchers in Mayo Clinic's Neural Engineering Laboratory also recently developed a series of translational and rotational adapters that expand the system's applicability to the entire cranial cavity. That work involved the novel application of conventional and geometric algebra, as described in Biomedical Engineering Letters.
As a major tertiary center, Mayo Clinic has the resources to provide optimal, personalized surgery for tremor. "Our goal is to significantly improve patients' quality of life," Dr. Ali says. "People can feel quite self-conscious about their tremor. We want to help them be much more engaged in social situations and do the things they love."
For more information
Jackson LM, et al. Clinical characteristics of patients with gait instability after MR-guided focused ultrasound. Tremor and Other Hyperkinetic Movements. 2021;11:41.
Rusheen AE, et al. A compact stereotactic system for image-guided surgical intervention. Journal of Neural Engineering. 2020;17:066014.
Sharaf B, et al. Expansion of stereotactic work envelope using transformation matrices and geometric algebra for neurosurgery. Biomedical Engineering Letters. In press.
Neural Engineering Laboratory: Kendall H. Lee, M.D., Ph.D. Mayo Clinic.
Refer a patient to Mayo Clinic.