Page 98 - IDF Journal 2023

IDF News – Spring 2023
MR-Guided Focused Ultrasound
The New Treatment for Essential Tremor
Mr Jonathan Hyam
Professor Ludvic Zrinzo
Tremor is a rhythmic shaking movement in one or more body parts and
can be resistant to medical therapy. A revolutionary new treatment is available at the Queen Square Imaging Centre that allows us to perform a deep brain neurosurgical procedure without needing to open the skin or the skull.
Tremor has many causes including physiological (anxiety, stress, metabolic), cerebellar, stroke/brain injury, drug induced (stimulants/beta agonists), dystonia, and orthostatic. Here, we shall focus on essential tremor and Parkinson tremor. It can sometimes be difficult
to distinguish the two, but Parkinson tremor tends to manifest as a rest tremor, classically pill-rolling, but can also include posture and action tremor. Parkinson tremor is associated with the other movement disorder features, including cogwheel rigidity, festinant gait, freezing, reduced arm swing when walking, slowness (bradykinesia), quietness
of speech and small handwriting (micrographia). Essential tremor is more common, with predominantly postural and action components. Patients
may describe a close relative with the condition, the tremor often improves with alcohol, and it can appear at any age.
The intrusiveness of the tremor
dictates whether treatment is required. This ranges from social stigma and embarrassment with difficulty drinking from a full cup, requiring a straw, and half
filling a cup, particularly with hot drinks, to disabling tremor that makes it difficult to undertake usual everyday activities such as writing and typing, dressing, cleaning oneself, and eating or preparing food.
The primary management for intrusive tremor is pharmacological, using a
beta antagonist such as propranolol, barbiturates such as primidone, and carbonic anhydrase inhibitors such as topiramate, initially as monotherapy with combination if necessary. In selected cases, botulinum toxin injections can reduce focal tremor severity. When tremor is medically intractable, severely disabling, limiting functions such as writing and working or socially embarrassing, one should consider neurosurgical treatment.
The brain circuit where the abnormal function is driving the tremor includes
the dentatothalamic tract, which runs between the cerebellum and the motor thalamus. Neurosurgeons target the motor nucleus of the thalamus to improve tremor of all types. This can be achieved by blocking the circuit with a high frequency electrical signal through a deep brain electrode into the thalamus. A cable connects to an impulse generator, much like a cardiac pacemaker. Deep brain stimulation is a common and established treatment for Parkinson’s disease, tremor, and dystonia. Another option is to create a small, targeted lesion within that circuit called a thalamotomy. This can be created by a probe passed through the brain via a small hole made in the skull and radiofrequency is used to ablate the small thalamic area at the tip of the probe. This can also be achieved by Gamma Knife radiosurgery that is currently under further study. More recently, thalamotomy has been achieved successfully by focused ultrasound.
Treating various diseases in the body using focused high frequency ultrasound is not new. However, the technology has only recently become available to deliver sufficient energy through the skull. The treatment is performed as a day case. A frame is pinned to the head under local anaesthesia. The procedure is undertaken in an MRI scanner that provides a map of thalamic location. The surgeon can then target this in three-dimensional space. The MRI also provides thermography
so that temperature within the brain can be monitored and provides confirmation that sufficient heat has been created
to denature protein at the target site, producing the lesion. The patient is tested during treatment, firstly to confirm the tremor is improving and that functions such as writing and drawing improve in real time during the treatment, as well as to confirm that adverse effects are not developing.
The landmark New England Journal of Medicine paper1 confirmed significant improvements in hand tremor scores using focused ultrasound compared
to sham procedure. Tremor, disability,
and quality of life improvements were maintained at 12 months. More recent publications have confirmed that treatment effect is maintained at five years of follow-up. NICE currently recommends focused ultrasound for essential tremor
in one arm. Globally, there is a greater experience with Parkinson’s disease tremor and even staged bilateral treatment that we hope to explore in the future.
Focused ultrasound thalamotomy has many advantages
• It is performed as a day case procedure.
• No skin incision or skull burr hole is required, thus eliminating infection and wound complications.
• Bleeding is extremely unusual.
• No maintenance, battery changes or electrical programming of implanted hardware is required.
• The procedure is performed under local anaesthetic and no general anaesthesia is required.
As a result, focused ultrasound appeals to many patients.
Installing a focused ultrasound system
at Queen Square Imaging Centre complements its cutting-edge neuro- imaging facilities. Our movement disorder neurosurgery unit is the UK leader in deep brain stimulation and tremor surgery, performing 1 in 3 of every such procedure in national audits, year-after-year. We
are thrilled to add focused ultrasound treatment to our range of patient options.
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