Abstract
Background and Study Aims Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is a highly effective
therapy for primary generalized and focal dystonias, but therapeutic success is compromised
by a nonresponder rate of up to 20%. Variability in electrode placement and in tissue
stimulated inside the GPi may explain in part different outcomes among patients. Refinement
of the target within the pallidal area could be helpful for surgery planning and clinical
outcomes. The objective of this study was to discuss current and potential methodological
(somatotopy, neuroimaging, and neurophysiology) aspects that might assist neurosurgical
targeting of the GPi, aiming to treat generalized or focal dystonia.
Methods We selected published studies by searching electronic databases and scanning the
reference lists for articles that examined the anatomical and electrophysiologic aspects
of the GPi in patients with idiopathic/inherited dystonia who underwent functional
neurosurgical procedures.
Results The sensorimotor sector of the GPi was the best target to treat dystonic symptoms,
and was localized at its lateral posteroventral portion. The effective volume of tissue
activated (VTA) to treat dystonia had a mean volume of 153 mm3 in the posterior GPi area. Initial tractography studies evaluated the close relation
between the electrode localization and pallidothalamic tract to control dystonic symptoms.
Regarding the somatotopy, the more ventral, lateral, and posterior areas of the GPi
are associated with orofacial and cervical representation. In contrast, the more dorsal,
medial, and anterior areas are associated with the lower limbs; between those areas,
there is the representation of the upper limb. Excessive pallidal synchronization
has a peak at the theta band of 3 to 8 Hz, which might be responsible for generating
dystonic symptoms.
Conclusions Somatotopy assessment of posteroventral GPi contributes to target-specific GPi sectors
related to segmental body symptoms. Tractography delineates GPi output pathways that
might guide electrode implants, and electrophysiology might assist in pointing out
areas of excessive theta synchronization. Finally, the identification of oscillatory
electrophysiologic features that correlate with symptoms might enable closed-loop
approaches in the future.
Keywords
deep brain stimulation - dystonia - globus pallidus internus - somatotopy - hot spot
