Pretherapeutic functional neuroimaging predicts tremor arrest after thalamotomy

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Excerpt

Essential tremor (ET) is the most common movement disorder.1 Considered initially a mono‐symptomatic disease of postural or action tremor, recent clinical, neuroimaging, and morphopathological studies2 rather see ET as a multi‐phenotype entity, with both motor and non‐motor symptoms. Its main feature, tremor, is usually bilateral, predominant on upper extremities, with a frequency between 4 and 12 Hz.1 An open question remains whether ET is of central or peripheral origin, and consequently the core role of the cerebellum versus the olivary complex has received great interest from the neuroscience community.4 Additional use of non‐invasive neuroimaging techniques5 or findings from deep brain stimulation (DBS)6 has pointed out toward an involvement of the so‐called tremor network (contralateral cerebellum; ipsilateral motor thalamus; and primary motor cortex).
Currently, three different views on ET are under debate: abnormal oscillations within the tremor network, progressive cell loss in the frame of a neurodegenerative disorder, or a localized GABAergic dysfunction.5
Primary treatment is pharmacological.7 Drug‐resistant ET can benefit from standard functional neurosurgery procedures (DBS or radiofrequency thalamotomy)8 or alternatively minimally invasive procedures, including radiosurgery (RS)9 or high‐focused ultrasound (HIFU).10 All aim at the same target, the motor thalamus part called ventro‐intermediate nucleus (Vim).
It is now well established that many diseases (including movement disorders) can be characterized by alterations in functional networks, which are spatially distant brain regions that interact to support brain function.2 Seminal work of Biswal et al12 demonstrated that during rest, blood‐oxygen‐level‐dependent (BOLD) time‐series, both primary motor areas exhibit a high correlation. Since then, several methodologies to extract functional connectivity or interconnectivity—if within a functional network—have been proposed to measure temporal dependencies of neuronal activation between anatomically separated brain regions.
Here, we performed pretherapeutic resting‐state fMRI in 17 patients, to clarify which networks and the statistically significant intercorrelated anatomical clusters would best correlate with clinical improvement, 1 year after stereotactic radiosurgical thalamotomy (SRS‐T, having delayed clinical effect [mean 4 months, going up to 1 year]).

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