Visual dysfunction of superior colliculus and lateral geniculate nucleus in idiopathic blepharospasm

Background: The etiology and pathophysiology of idiopathic blepharospasm (BP) are still largely unknown. It has been hypothesized that BP is the consequence of a dysfunction of the basal ganglia loop, although cortical areas, cerebellum, and other brainstem structures may be involved. There is some evidence that the superior colliculus (SC), a sensorimotor brainstem structure, is involved in another adult-onset focal dystonia, the cervical dystonia. To date, there is no data concerning the implication of the SC in BP. Objectives: Our study aims to investigate the role of the SC in people with idiopathic BP compared to controls using fMRI and a visual stimulation paradigm based on luminance contrast variations. Methods: People with idiopathic BP and controls underwent brain fMRI using a standardized protocol, allowing modulation of visual activity in the SC, the lateral geniculate nucleus (LGN), and the primary visual cortex (V1), at increasing luminance levels (1 %, 3 %, 5 %, 9 %). Results: Ten BP women and ten sex- and age-matched controls were enrolled. Compared to controls, the BP group showed no modulation of visual responses at all luminance levels (p < 0.05) in both SC and LGN. In BP, BOLD responses in V1 were significantly lower at 5 % (p = 0.001), and 9 % (p = 0.002) luminance level. Conclusions: Our findings support the concept of SC and LGN dysfunction in idiopathic BP. Brain fMRI, targeting these sub-cortical visual structures, could play a future important role both as a biomarker and in our understanding of the pathophysiology of adult-onset focal dystonias.