Assessment of the retina nerve fiber layer and macular thickness by optical coherence tomography in patients with hereditary neurodegenerative movement disorders

Abstract

Hereditary neurodegerative movement disorders are a group of diseases with clinical, electrophysiological and genetic characteristics quite varied that having in common the preferential involvement of motor neurons and progressive and chronic course. In this study, we will analyze Friedreich's ataxia and hereditary spastic paraparesis. Friedreich's ataxia (FA) is the most common hereditary ataxia with a prevalence of 1 per 3050 thousand individuals and is more common in Europe and North America. It is an autosomal recessive neurodegenerative disease resulting from mutations in the FXN gen, located on chromosome 9, which encodes a mitochondrial protein called frataxin. The decrease in frataxin protein causes a change in iron metabolism within the mitochondria, causing iron accumulation and cell death. The main clinical manifestation of FA is a progressive limb and gait ataxia presenting prior to 25 years. Therefore, dysarthria, changes in proprioception and deep sensitivity, scoliosis, diabetes and cardiomyopathy are present in the patients with FA. Ophthalmic manifestations are present in patients with FA and change in eye movements that cause loss of fixation as saccadic oscillations, horizontal nystagmus and disorder of pursuit are most common. Slowly visual loss associated with optic nerve atrophy may also affect patients with FA. Hereditary spastic paraparesis (HSP) is a group of neurodegenerative disorders with different clinical and genetic characteristics. Progressive slowly weakness and spasticity of lower limbs are the principal manifestations. The HSP are classified as pure and complicated subtypes. In pure form, the involvement is limited to the lower limbs. In complicated form, other manifestations such as peripheral neuropathy, ataxia and cognitive deficits are present. Ophthalmologic manifestations in complicated HSP are not common and, when it occurs, optic atrophy (with or without vision loss) and change the pigmented retina are more frequently. Optical coherence tomography (OCT) is a diagnostic tool widely used in ophthalmology for evaluation of axonal loss associated to optic neuropathies. In neurology, there are many studies with neurodegenerative diseases such as multiple sclerosis, Alzheimer's disease and Parkinson's disease evaluating the potential of OCT as a biomarker of progression of disease and response to treatment. The major objective of this project is to measure the peripapillary nerve fibers thickness and macular thickness of patients with FA and HSP using OCT and evaluate its potential as biomarker in these hereditary neurodegenerative movement disorders. (AU)