11: DBS

Question 1

functional neurosurgery

Answer 1

surgically altering NS in order to treat symptoms of neurologial + psychiatric illness

Question 2

stereotactic neurosurgery

Answer 2

technique where any point in the brain can be defined according to a 3D cartesian coordinate system, allowing targets situated at specific coordinates to be reached by an intracranial probe

Question 3

proposed mechnsm of action in lesioning

Answer 3

reduce overactivity in a particular area of the brain + the symptoms it causes, by partially destroying it with heat or caustic substance

Question 4

the key to DBS?

Answer 4

make stimulation approach as minimally invasive as possible so as to avoid unnecessary damage to brain

Question 5

major advance with DBS?

Answer 5

combining sterotaxis + small calibre electrodes

Question 6

estimated # patients currently treat with DBS

Answer 6

world wide: 150 000 (90 000 for PD)

Question 7

DBS definition

Answer 7

treatment of various pathological disease states by the chronic + reversible use of direct electrical current, applied focally to subcortical neural elements, aiming to alter function of these structures either in isolation or in relation to their role w/i larger networks/circuits

Question 8

5 parts in DBS

Answer 8

electrodes, leads, extension, neurostimulator + patient programmer

Question 9

steps to performing DBS

Answer 9

apply sterotactic frame (coordinate system). image pt’s brain and identify target, record + stimulate to define target electrophysiologically, affix electrodes implant pulse generator. DBS turned on after 4 weeks.

Question 10

modifiable stimulation parameters: 4?

Answer 10

voltage/current. pulse width. frequency. electrode configuration (monopolar, bipolar)

Question 11

DBS: what do you want the generated electrical field to maximize/minimize?

Answer 11

maximize stimulation to target, minimize excitation of surrounding structures

Question 12

in contrast to traditional lesioning surgery, DBS is (3)?

Answer 12

reversible, adjustable and titratable

Question 13

key considerations for safety

Answer 13

stimulation side effects (so location very important). hardware related failure. infection. intracerebral hemorrhage

Question 14

why use DBS for PD when there are drugs?

Answer 14

motor symptoms respond well to L dopa, but many pts become refractory or develop side effects from prolonged use: end of dose deterioration, peak dose dyskinesias

Question 15

2 sites for DBS for PD and overall result

Answer 15

globus pallidus internal segment + subthalamic nucleus = overall increased drive from thalamus to cortex= movement

Question 16

DBS for PD: main mechanism of action?

Answer 16

disrupts pathologic oscillatory patterns and generates an information lesion

Question 17

what letter oscillations and where? DA?

Answer 17

beta-band oscillations: normally present in cortex but dampened with activity. low dopamine = self correction breaks down so they aren’t dampened in PD: DBS will reduce these beta oscillations = movement

Question 18

DBS and circuits?

Answer 18

modulates activity within dysfunctional brain circuits at specific nodes, either restoring functional activity or replacing dysfunctional activity with a therapeutic new normal

Question 19

DBS for essential tremor: what is ET? target?

Answer 19

most common mvt disorder (4%) involuntary, rhythmic, oscillatory contraction of agonist/antagonist muscles. target the thalamus

Question 20

fornix DBS: memory

Answer 20

may preserve memory function in AD

Question 21

fornix DBS: result for metabolism

Answer 21

produces a reversal of hypometabolism in pariet-occiptal regions, known to be underactive in AD

Question 22

DBS slowing down neurodegeneration?

Answer 22

see hippocampal neurogenesis (animal models). also increases blood vessel area and synaptic density

Question 23

DBS and AD: brain structure?

Answer 23

saw that hippocampus enlarged in some patients: unprecedented! volume change correlated to clinical outcome

Question 24

conclusion: DBS is a ___ therapy, for ___? works by?

Answer 24

an effective symptomatic therapy for several neurological + neurodegen. diseases. works by altering activity in a dysfunctional neural circuit.