Deep Brain Stimulation Flashcards
What is deep brain stimulation?
Procedure in which stimulating electrodes are placed stereotactically into certain deep brain structures
100Hz frequency parameter
What is the mechanism of DBS?
Electrodes connected to implanted pulse generator
- electrodes secured to skull
- cable tunnelled around ear down neck to generator which is in front of chest
- battery replacements for generator required every 3-4 years
- rechargeable systems developed with lifespan of 10 years
What is DBS used for?
NHS funded
- Parkinson’s (hypokinetic)
- essential tumour (hyperkinetic)
- dystonia (hyperkinetic)
Individual funding requests
- epilepsy
- chronic neuropathic pain
What is being experimented with DBS?
- treatment of psychiatric disorders
- dementia
- eating disorders
- disorders
What is dystonia?
brain disorder with sustained or repetitive muscle contractions resulting in twisting and repetitive movements/abnormal fixed postures
What is the criteria in DBS for Parkinson’s disease?
- idiopathic PD
- 4 classical symptoms (rigidity, tremor, bradykinesia, postural instability)
- do not have sensory issues (as would therefore be related to nerves and would not be Parkinsons)
- do not get weakness/hyper-reflexia (would be affecting pyramidal tract so not idiopathic Parkinsons)
- require MRI scan to check for abnormalities
- no mental disorders
- treated with levodopa (as response to levodopa is good confirmation of Parkinsons)
- still respond to levodopa (DBS will not work if no dopamine neurons available)
- physically fit for surgery
- realistic expectation of surgery (not a cure but will help with motor symptoms)
- age (younger the better?)
What symptoms of Parkinsons does DBS treat?
Only the motor symptoms
How is DBS carried out for Parkinson’s?
- ensure patient has washed hair with anti-bacterial shampoo, emptied bowels, had good sleep
- patients not on medication so will arrive at hospital slow and stiff
- use MRI scan to work out target site
- connect stereotaxic frame on patient’s head/do 3D printing of skull to create something that fits on after some anaesthetic as frame can be painful
- shave hair off
- drill 4cm hole into skull, insert microelectrode tip to target site
- each brain structure has distinct neurophysiological spiking
- remove microelectrode and insert stimulating electrode
- cap hole, close would, MRI scan to confirm correct electrode site and general anaesthesia for neurostimulator implant
- return home next day, 1 month later return to clinical programme DBS and adjust drug dosage
What are the effects of DBS on Parkinsons?
- increases ‘on’ time (time where drug is working - still have to take levodopa but less of it)
- decrease bradykinesia and rigidity
- reduce medication dose
- improves dyskinesia as less drug required
- effectively treats tremor (levodopa not good with tremor)
Which brain regions does DBS work on?
- zona incerta (tremor)
- subthalamic nucleus (tremor)
- global pallidus internal (dystonia and tremor)
When and how does DBS treat epilepsy?
- when medications are inadequate
- epilepsy surgery not always possible as cannot identify focal brain region (remove seizure origin)
- electrode implanted into anterior nucleus of thalamus as part of brain which spreads seizure
- only reduces do not eliminate seizure frequency
- benefits 50-60% epileptic patients so NICE do not fund, have to make individual funding requests
How does DBS treat chronic neuropathic pain?
- treat pain when medications are inadequate
- surgery via lesion to brain regions related to pain pathway is more invasive than DBS
- only reduce NOT eliminate pain experience
- benefits 15-50% of pain in patients
What is pallidotomy?
Make a lesion to the globus pallidus use an electrical probe of 80 degrees Celsius for 1 minute
What is thalamotomy?
make a lesion to the thalamus using an electrical probe of 80 degrees Celsius for 1 minute
What are the 3 types of tremors?
- resting tremor
- Postural tremor (shaking whilst putting hand up)
- Intentional tremor (shaking whilst trying to do something e.g. writing)
What is essential tremor?
A brain disorder causing part of body (head and forearms) to tremor uncontrollably
Often genetic
What types of causes can induce Parkinsons?
Idiopathic
Vascular Parkinsonism
Drug Induced Parkinsonism - e.g. drugs to be used for schizophrenia
What is the function of the thalamus?
Central control as everything leaving the brain and coming up from spinal cord passes through thalamus
What happens to levodopa dose overtime?
Dosage increases - have to take it more frequently as effects are worn off quicker
Also dyskinesia worsens as you take more
What are some other regions/uses for DBS?
Resistant Depression - Brodmann area 25
Anorexia - hypothalamus
Addiction - nucleus accumbens
Alzheimer’s disease - anterior of fornix
What are the pros of DBS?
- proven safe, no deaths
- effective in treating movement disorders
- improves tremor which are levodopa resistant
- effects are reversible and area can be tailored to patient’s clinical status
- patients who have undergone DBS are still candidates for other treatment options - stem cell/gene therapy
- allows decrease in medication/makes medication more tolerable
What are the cons of DBS?
- 2-3% risk of brain haemorrhage causing paralysis/stroke/speech impairment (so tell patients week before to stop taking aspirin/heparin)
- small risk of CSF leakage = headaches and meningitis
- 15% risk of temporary problems with transplantation = infection/allergy to implant so have to take it out and redo
- temporary tingling in face/limbs, loss of balance, dizziness, concentration issues
- migration of electrodes from original implantation site
- temporary rebound in worsening of tremor when stimulation stopped
- no absolute guarantee DBS will benefit patients
What are the 4 hypothesis for DBS mechanism of action?
1 - inhibition hypothesis
2 - excitation hypothesis
3 - disruption hypothesis
4 - neuro-network modulation hypothesis
What is inhibition hypothesis?
- PD due to overactive basal ganglia in STN and op GPi
- DBS can block this removing spontaneous discharge from GPi neurons
- if give GABA agonists/lesion GPi alleviate problem
What is excitation hypothesis?
Neurones in the thalamus have an a.p and go from cell body to synapse = orthodromic
- too much activation of the cortex
- DBS excites afferent axons so creates excitation in the opposite direction towards cell body (antidromic) = ‘jamming’ of spontaneous activity= reduction of excitation of cortex
What is the disruption hypothesis?
- have direct, indirect and hyperdirect pathways (doesn’t go through striatum) which all terminate in GPi
- by stimulating the GPi you disrupt/block flow before it goes to thalamus stopping GPi functioning
What is the neuro-network modulation hypothesis?
- explains delayed effect of DBS
- involves neuroprotection, release of astrocytic gliotransmitters, electrotaxis, cortical plasticity which all result in DBS working
