Deep Brain Stimulation
- Three
common targets: STN, GPi, VIM
- STN
- Indication
– Parkinson’s disease that is starting not to respond to
medication
- “on-off”
effect; dystonic when medication level high and parkinsonian when level
low
- Coordinates
(relative to MCP): 12.5 mm lateral, 4 mm posterior, 5 mm inferior
- Trajectory:
25 degrees anterior, 15 degrees lateral
- Done
with microelectrode recording (variation on ideal depth)
- Usually bilateral
- On way
to target:
- white
matter
(quiet)
- thalamus (irregular with occasional
bursts, like “popcorn” or “rain on a roof”)
- white
matter of
zona incerta/fields of forel (quiet)
- STN (sounds irregularly
irregular like “grand central station”)
- white
matter
(quiet)
- substantia
nigra part reticularis (regular fine delicate)
- Confirmatory:
move arms or legs – will cause burst of activity if in STN
- If off
target:
- Too
lateral or posterior – internal capsule (quiet on microelectrode,
will get tonic deviation of extremities if stimulatied)
- Too
medial or anterior – hypothalamus (will get tonic eye deviation)
- not to
be confused with transient clinically insignificant limitation of EOM
when STN stimulated for the first time
- GPi
- Indication
– dystonia that is unresponsive to medical management
- Coordinates
(relative to MCP): 20 mm lateral, 2 mm anterior, 5 mm inferior
- Trajectory:
15-20 degrees anterior, 0 degrees lateral (more if pathway crosses
ventricle)
- Can be
done either with microelectrode recording or testing by
stimulation
- too
deep if stimulates optic tract, too shallow if stimulates internal
capsule for tonic deviation
- Bilateral
- On way
to target:
- Putamen
- GPe
- GPi
- white
matter
- optic
tract
- Like
aiming at apex of cone; globus pallidus is pivot point of brain rotation
during development
- Confirmatory:
stimulate eyes with flash during microelectrode recording – too deep if
get bursts
- If off
target:
- Too
lateral – GPe (different microelectrode pattern)
- Too
medial, posterior, or anterior – internal capsule white matter
- VIM
- Indication
– tremor
- Coordinates
(relative to MCP): point halfway between MCP and PC (usually about 6 mm
posterior), 13.5 mm lateral, 0-2 mm superior
- Alternate
method: traversing rhomboid area running diagonally from line on AC-PC
line between 3/6 and 4/6 of the way between MCP and PC and line at the
top of the thalamus between 2/6 and 3/6 of the way between MCP and PC
- Trajectory:
25 degrees anterior, 15-25 degrees lateral
- Done
with testing by stimulation only (difficult to use microelectrode
recording within thalamus)
- Classically
start posteriorly at VC (=VPM and VPL relay nuclei) to get paresthesias,
move tract forward until stimulation produces desired response
- VIM
somatotopic (legs lateral, arms medial) so must aim for most affected
limb
- If in
right place: stimulation at 10 Hz will drive tremor, stimulation at 100
Hz will suppress tremor
- Can be
unilateral or bilateral depending on symptoms (but only one
side done at a time to prevent risk of aphasia)
- On way
to target:
- white
matter
- caudate
- thalamus
- white
matter
- Confirmatory:
stimulation
- If off
target:
- Too
posterior – VC (paresthesias)
- Too
anterior – VOA (no effect of stimulation)
- Too
lateral/medial – wrong part of somatotopic organization so no effect in
desired limb
- Other
targets: PVG for pain (rarely used), hypothalamus for
cluster headaches (anterior/deep/medial to VIM)