Target
- Sensory thalamus
- Ventral posteromedial (VPM) OR
- Ventral posterolateral (VPL)
- Motor cortex stimulation: Chronic stimulation of the precentral gyrus below the threshold to produce a motor response is able to alleviate certain types of deafferentation pain
- Periaqueductal gray
Explanation for pain targets for DBS
- The spinothalamic and spinoreticulothalamic tract terminate in the
- Medial (CM/Pf and CLp) AND
- Medial thalamic lesions have focused on the destruction of the CM/Pf.
- The efferent from these thalamic nuclei to associative and paralimbic areas provides an additional target to modulate the affective component of pain.
- Lateral lesions focus on the posterior centrolateral nucleus (CLp).
- Bilateral receptive fields from laminae V-VII travel via the spinothalamic tract to the CLp, from which it has diffuse efferent projections to the primary somatosensory cortex, insula, and anterior cingulate cortex as well as shorter projections to the thalamic reticular nucleus.
- Lateral thalamus (ventral posterolateral nucleus [VPL]/ventral posteromedial nucleus [VPM]),
- Destruction of the VPL/VPM interrupts these specific pain pathways, which project somatotopically to primary sensory cortex and are thought to subserve the discriminatory aspect of pain.
Indicated in
- Deafferentation pain syndromes
- Eg
- Anaesthesia dolorosa
- Pain from spinal cord injury
- Thalamic pain syndromes
- Stimulation of
- Sensory thalamus
- Ventral posteromedial (VPM) OR
- Ventral posterolateral (VPL)
- Centro-median parafasicular region (CM/Pf) of the thalamus,
- Motor cortex stimulation: Chronic stimulation of the precentral gyrus below the threshold to produce a motor response is able to alleviate certain types of deafferentation pain
- MCS has shown efficacy for a number of deafferentation pain syndromes (e.g. trigeminal, central post-stroke pain, anesthesia dolorosa, post-herpetic neuralgia, multiple sclerosis, phantom limb pain, and spinal cord injury).
- Mechanism of action
- Modulation of deafferentation-induced pathologic hyperactivity in thalamic relay nuclei and/or
- Increased sensitivity of higher order pain pathway neurons.
- Technique
- Intraoperatively, the central sulcus is localized using SSEPs and a contact paddle electrode is placed in the epidural space overlying the facial or upper extremity region of the motor cortex.
- The electrode is then used for motor evoked potentials with electromyography to confirm motor activity.
- Iced saline is prepared for irrigation if a seizure is induced.
- The minimum thresholds for motor activity and any seizure activity are noted. After confirmation, a paddle electrode is sutured to the dura over the precentral gyrus over the motor area that corresponds to the patient’s pain distribution.
- Subdural placement is associated with greater energy efficiency, but also an increased rate of complications, including subdural hematomas and a higher reported rate of seizures.
- However, opening of the dura may be necessary anyway for coverage of lower extremity pain, which requires placement of an electrode along the medial part of the hemisphere.
- MCS has an overall complication rate of about 5%:
- Wound breakdown or infection (5.1%),
- Hardware breakage from trauma, and seizures (12%).
- Seizure
- Stimulation of the motor cortex is known to be associated with the potential to induce seizures, and most seizures observed during MCS occur during programming sessions.
- Chronic neuropathic pain
- Produces a 40–50% reduction in pain in about 25–60% of patients.
- Nociceptive pain syndromes
- Stimulation of
- Periventricular gray matter (PVG) OR
- Periaqueductal gray matter (PAG),
- Although PAG stimulation is rarely used because it often produces unpleasant side effects.
- Not approved by FDA
- Response rate has been only ≈ 20%,
- Cluster headaches:
- Stimulate hypothalamus
- Still awaiting more study
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