Retinal nerve fibre layer thickness in ARSACS: myelination or hypertrophy?

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) was first described in the French-Canadian founder population of Quebec in 1978, but genetically confirmed patients have now been reported in individuals from Europe and Japan. Ataxia, dysarthria, spasticity with extensor plantar reflexes, distal muscle wasting, sensorimotor neuropathy and horizontal gaze-evoked nystagmus constitute the most frequent progressive neurological signs. Neuroimaging reveals atrophy of the superior vermis, cervical spinal cord, and cerebral cortex. SACS is the most frequent gene associated with ARSACS. Previous authors reported that retinal hypermyelinated fibres observed in funduscopy are a minor diagnostic criterion for ARSACS that may identify patients with early-onset cerebellar ataxia and characteristic pontine abnormalities. 3 We found patients with full ophthalmological examination and retinal nerve-fibre layer (RNFL) photographs showing significant increases in RNFL thickness compared to healthy subjects, but not the myelinated fibres radiating from the optic disk described by previous authors. In addition, digital imaging technologies such as optical coherence tomography to measure peripapillary RNFL thickness and provide retinal images show an increase in the RNFL density in these patients. These findings suggest that RNFL hypertrophy in ARSACS patients was interpreted as hypermyelinated retinal fibres in previous reports, and thus the ARSACS diagnostic criteria, particularly with regard to retinal alterations, should be revised. Increases in RNFL density cause retinal streaks observed in the funduscopy exam that may be confused with