For tremor
Indication
- Best candidates
- Medical treatment resistant tremor
- Essential tremor only
- Older age range (as uncertain data re longevity)
- Happy with unilateral treatment
- Severe tremor, 2-3cm amplitude postural or kinetic tremor
- No MRI contraindications
- Very good tandem walking, good speech
- MMSE >25/30. Not frail
- Does not want or ineligible for DBS
- Tremor-predominant PD
- It is important to confirm the clinical diagnosis of idiopathic PD or benign essential tremor since Parkinson’s plus syndromes have a much poorer prognosis after thalamotomy.
- Thalamotomy and thalamic stimulation have only a small role in current PD management because GPi and STN stimulation provides better control of symptoms other than tremor (hence even patients who are tremor dominant will develop other symptoms with time which will not benefit from thalamic stimulation).
- Incapacitating benign essential tremor.
- Less predictable outcomes are seen with tremor and hemiballismus/chorea due to
- Damage of the
- Cerebellar tracts from cerebrovascular accidents, trauma or multiple sclerosis,
- Primary and secondary dystonias.
Target
- VIM
- What is MRgFUS?
- Under MR guidance, >1000 ultrasound beams are directed towards the VIM thalamus
- Initial low power sonifications (at 40-45c) produce transient test lesions to assess efficacy/side effects
- Followed by lesion creation (at 60c) to produce clinical effect
- How does it compare to DBS?
- MRgFUS is less invasive (less infections/battery replacements etc)
- Less hospital visits
- Similar efficacy, although long term data less certain in MRgFUS
- MRgFUS can only be unilateral (DBS can be bilateral)
- Risks of permanent side effects paraesthesia (14%) and balance issues (9%) at 1 year in MRgFUS (higher than DBS)
- MRgFUS is not modifiable (vs DBS)
CI
- Cognitive decline
- Speech disorders
- Serious systemic disease
- Advanced age
For Pain
- Theories of imbalance between the medial (nonspecific) and lateral (specific) groups form the basis for some thalamic procedures for pain.
- Indication
- Best candidates
- ≥ 1 year of medically refractory neuropathic pain for contralateral thalamotomy.
- Target
- Medial thalamus (SRS)
Complications of thalamotomy
- Due to
- Inaccurate lesion placement or
- Overly large lesions
- Types of complications
- Contralateral weakness
- Lesions placed too laterally
- Due to injury of the posterior limb of the internal capsule (face and arm).
- Contralateral hemisensory deficits
- Lesions placed too posterior
- Due to injury of the VC nucleus (e.g., numbness or paraesthesia of the mouth or fingers).
- Transient dysarthria or dysphasia
- Transient confusion
- Some may persist permanently
- Left thalamic lesions
- Increased risk for deficits in learning, verbal memory and dysarthria
- Right thalamic lesions
- Increased risk of impaired visuospatial memory and nonverbal performance abilities.
- Bilateral thalamotomies are associated with deficits in memory/cognition and speech problems (e.g., hypophonia, dysarthria, dysphasia, and abulia) in up to 60%, hence should not be undertaken routinely
- Where they must be done it should be staged and slight variation in the target coordinates between sides may reduce major side effects.
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