Occurrence of eye movement disorders in motor neuron disease

The diagnosis of amyotrophic lateral sclerosis (ALS) relies on symptoms and signs related to upper and lower motor neuron injury. Preservation of normal ocular motor movements is an important criterion for making this diagnosis as oculomotility pathways are classically spared in ALS. However, some authors report eye disturbances resulting from nuclear and supranuclear ophthalmoplegia in autopsy-proven ALS. Here, we report a case in which eye movement disorders were an early sign associated with a bulbar-onset ALS. The association of progressive ophthalmoplegia, dysexecutive syndrome and automatico-voluntary dissociation of eyelid occlusion suggested a 'progressive supranuclear palsy variant' of ALS caused by a disturbance in the descending frontal projections, even though morphological imaging was normal. Motor neuron disease with eye movement disorders must not be considered as a distinct clinical entity and must not exclude a diagnosis of ALS.