Magnetic Resonance-Guided Focused Ultrasound (MRgFUS) Thalamotomy for Parkinson's Disease Tremor
MRgFUS thalamotomy of the ventral intermediate nucleus (VIM) is the ultrasound therapy used to treat medication-refractory tremor in Parkinson's disease, providing sustained tremor improvement with a superior safety profile compared to other surgical options. 1, 2
Clinical Indications
MRgFUS thalamotomy should be considered for Parkinson's disease patients who meet the following criteria:
- Failed treatment with at least 2 medications, including a first-line treatment, due to lack of efficacy, intolerance, or medical contraindication 2
- Tremor significantly interfering with quality of life and functional activities 2
- Unilateral or predominantly unilateral tremor (bilateral treatment is contraindicated) 1, 2
Efficacy and Durability
The procedure demonstrates robust and sustained tremor control:
- Immediate cessation of tremor in the treated hand following treatment 3
- 62% of treated patients show improvement in tremor scores at 3 months compared to 22% in sham controls 4
- Sustained tremor improvement of 56% at 2-4 years 1, 2
- Motor UPDRS scores improve by approximately 46% at 6 months, with improvements in rigidity (71%) and tremor (77%) 3, 4
- Quality of life scores (PDQ-39) improve by 47% at 6 months 3
Important caveat: Tremor relapse occurs in approximately 23% of patients, exclusively during the first month after thalamotomy, and is associated with younger age and smaller lesion volumes 5
Safety Profile and Adverse Events
MRgFUS has a significantly lower complication rate (4.4%) compared to radiofrequency thalamotomy (11.8%) and deep brain stimulation (21.1%). 1, 2, 6
Common transient adverse effects during the procedure include:
Post-procedure adverse effects at 3 months:
- Gait imbalance (38%) 7
- Sensory deficits (26%) 7
- Motor weakness (18%) 7
- Dysgeusia (6%) 7
- Dysarthria (6%) 7
Most adverse events are mild and resolve: Early adverse effects like gait disturbance (36%) and paresthesias (38%) decrease to 9% and 14% respectively by 1 year, with no adverse events lasting beyond 3 months in most series 1, 3. At 1 year, only 6% of patients have persistent adverse events 7. Serious adverse events are rare (1.6%) 1.
Contraindications
Absolute contraindications to MRgFUS thalamotomy:
- Inability to undergo MRI for medical reasons 1, 2, 6
- Skull density ratio <0.40 1, 2, 6
- Bilateral MRgFUS thalamotomy or contralateral to a previous thalamotomy 1, 2, 6
Treatment Algorithm for Surgical Candidates
For unilateral tremor or patients with medical comorbidities: MRgFUS thalamotomy is preferred due to its lower complication rate 1, 2
For bilateral tremor involvement: Deep brain stimulation should be considered instead, as bilateral MRgFUS is contraindicated 1, 2
For younger patients: Consider that tremor relapse is more common in younger patients and may be associated with smaller lesion volumes 5
Optimal Lesion Parameters
A lesion volume between 145 and 220 mm³ on T1-weighted MRI appears to be the therapeutic window that ensures tremor control without long-lasting adverse events. 5 Smaller lesions are associated with higher relapse rates, while larger lesions increase the likelihood of persistent adverse events 5.
Procedural Details
- Average of 21 sonications are required (range 14-45) 3
- Mean maximal temperature of 56.5°C (range 55°-60°C) 3
- Mean maximal energy of 12,500 J (range 5,850-23,040 J) 3
- MRI performed <24 hours post-procedure to assess lesion 7
Common Pitfall
Bradykinesia may temporarily worsen post-procedure due to edema around the target, which should not be mistaken for treatment failure. 8 This typically resolves as edema subsides.