ANIMAL-MODEL EXPLAINS THE ORIGINS OF THE CRANIAL DYSTONIA BENIGN ESSENTIAL BLEPHAROSPASM

The current study demonstrates that combining two mild alterations to the rat trigeminal reflex blink system reproduces the symptoms of beni gn essential blepharospasm, a cranial dystonia characterized by uncont rollable spasms of blinking. The first modification, a small striatal dopamine depletion, reduces the tonic inhibition of trigeminal reflex blink circuits. The second alteration, a slight weakening of the lid-c losing orbicularis oculi muscle, begins an adaptive increase in the dr ive on trigeminal sensory-motor blink circuits that initiates blepharo spasm. By themselves, neither of these modifications causes spasms of lid closure, but combined, they induce bilateral forceful blinking and spasms of lid closure. A two-factor model based on these rodent exper iments may explain the development of benign essential blepharospasm i n humans. The first factor, a subclinical loss of striatal dopamine, c reates a permissive environment within the trigeminal blink circuits. The second factor, an external ophthalmic insult, precipitates benign essential blepharospasm. This two-factor model may also be applicable to the genesis of other cranial dystonias.