An Unusual Fundus Finding in a Teenage Girl

C. Autosomal recessive spastic ataxia of Charlevoix-Saguenay

Brain magnetic resonance imaging (MRI) showed upper cerebellar vermis atrophy, linear pontine T2 hypointensities, lateral pontine T2 hyperintensities, a posterior fossa arachnoid cyst, and thinning of the corpus callosum and cervical spinal cord (Figure 2). Per the clinical features, fundoscopy findings, and abnormalities on MRI, autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) was suspected. Genetic testing identified biallelic pathogenic SACS mutations.

The first description of ARSACS derives from families of the Charlevoix and Saguenay regions of Quebec, Canada. The patients had unsteadiness and falls at gait initiation, followed by slowly progressive spastic ataxia and axonal-demyelinating peripheral neuropathy. Every affected individual presented with slurred speech, saccadic pursuit, and nystagmus, accompanied by a distinctive fundus appearance involving an increased visibility of the retinal nerve fibers hiding parts of the retinal vessels.¹ Identification of the causative gene, SACS, and its product, the protein sacsin, occurred in 2000. Outside of Canada, most patients have disease onset in the first decade of life and display progressive spastic ataxia and peripheral neuropathy. However, retinal abnormalities are less frequent in non-Canadian individuals, and divergent presentations may exhibit adult onset, hearing loss, and supranuclear vertical gaze palsy.² Moreover, the ataxia, spasticity, and peripheral neuropathy of the classic ARSACS triad might each be missing in patients with SACS mutations.³ Findings on MRI include upper cerebellar vermis atrophy, linear pontine T2 hypointensities, lateral pontine T2 hyperintensities, thickening of middle cerebellar peduncles, posterior fossa arachnoid cyst, corpus callosum thinning, and parietal atrophy.³ Optical coherence tomography reveals thickening of the RNFL, which is unknown in any other progressive neurodegenerative condition. Also, OCT is more sensitive in detecting retinal abnormalities in ARSACS compared with fundoscopy.⁴