Focused Ultrasound (MRgFUS)
MRI guided focused ultrasound (MRgFUS) is an innovative new treatment option for medication refractory tremor. It is estimated that up to 4% of the population has essential tremor with many individuals having a severe form suitable for this therapy. Up until recently, severe tremors required surgical treatment with deep brain stimulation or radiofrequency ablation. With the advent of focused ultrasound, the ability to target areas of the brain accurately without the risks of surgery has led to a surge in the number of people being treated worldwide.
This technique was first approved in 2016 for the treatment of essential tremor. With experience, the indications have expanded to include other tremor disorders and Parkinson’s disease. The procedure is conducted within an MRI scanner with the patient awake and able to titrate treatment response. The response is immediate and dramatic with patients displaying an improvement in measures of disability and quality of life.
How it works:
The MRgFUS system encloses the head in the MRI scanner and directs high frequency ultrasound waves through the scalp. 1024 transducers direct ultrasound energy into a focal point to create very small lesion within the area of the brain responsible for aberrant tremor generation (Figure 1). The system is tailored to deliver an initial reversible test dose in order to establish the correct location and effect. A final dose creates a permanent lesion that is visible on MRI. This has the effect of interrupting the cerebellothalamocortical pathway responsible for tremor. Treatment is delivered to a single side of the brain at present but studies of bilateral treatment are underway.
How effective is it:
The first randomised trail was published in 2016 which led to FDA approval. It showed a 65% improvement in disability and 55% improvement in tremor scores. Subsequent trials have shown even greater improvements in disability of up to 80% and tremor scores of between 65-75% (Figure 2). The effect of treatment is maintained long term and 4 yr data has shown a very low rate of tremor recurrence. The treatment effect size equal to and likely better than that seen with traditional surgical approaches to tremor.
Side effects are mild and typically last less than 3 months. The main side effects observed have been oral or hand numbness (15%), limb weakness (1%) and unsteadiness (4%). 79% of adverse events are deemed mild and the rate of serious events is < 1%. No brain haemorrhages have occurred with MRgFUS treatment to date.
By comparison, surgical approaches for tremor have an adverse event rates of 15% with 2-3% being serious.
At present the procedure is approved for essential tremor and tremor dominant Parkinson’s disease. The targeting varies depending on the underlying indication. In time it is expected that other movement disorders will gain approval.
Patients are first seen by a Neurologist with experience in movement disorders. A definitive diagnosis and certain basic investigations are required prior to selection for the procedure. Patients require CT and MRI brain imaging prior to treatment and may be excluded if found to have low skull density ratio. The latter determines the amount of energy that can be delivered via the system. The Neurologist will explain the procedure in detail and then obtain consent. At present there are only 2 sites in Australia offering MRgFUS. Dr Ahmad has expertise in this field and can offer this service to Sydney patients.
At present this procedure is not covered by Medicare in Australia. Given the strong data from clinical trials and progress overseas with reimbursement, it is hoped that this will change in the near future. There are a number of finance options available that can be discussed prior to evaluation. This can substantially offset or eliminate difficulty with affordability.
A treatment takes on average 3-4 hrs. Planning is undertaken several weeks prior and involves the treatment team agreeing to a target and treatment plan.
Post procedural care:
Following the procedure, patients typically require an overnight hospital stay as a precaution and for observation. Follow-up is made at the 3 month mark at which time tremor assessments are carried out for research purposes.
Neurologist: Determines the diagnosis and performs tremor evaluation and responses while in the MRI scanner. Responsible for follow up care.
Neurosurgeon: Positions patient and head in stereotactic frame. Determines the optimal target and performs sonications.
Radiologist: Operates the MRI scanner and performs specialised MRI sequences for thermal imaging, fusing of images and highlighting vital tracts.