Abstract
Purpose: :
Pelizaeus-Merzbacher disease (PMD) is a X-linked developmental defect of myelination affecting the central nervous system. Ophthalmic clinical features are early nystagmus, optic atrophy and severe loss of visual acuity. The aim of this study is to characterize the ophthalmologic impairment in PMD, its relation with dysmyelination, to identify cerebral structures involved using a new tool, the diffusion tensor imaging (DTI) quantifying myelination and axonal damage.
Methods: :
Prospective study including 20 PMD children (mean age =11.3 ) and their parents as control( mean age=40) followed between 2005 and 2009 in compliance with the declaration of Helsinki. Protocol included neurologic, ophthalmologic and radiologic examination. PMD children were divided in 3 groups according to the delay in motor development and in 4 groups according to their visual acuity. MRI datas were analyzed with DT I Studio to calculate fractional anisotropy, radial and axial diffusivity in regions of interest : cerebellar white matter, optic radiations, pons and calacarine cortex.
Results: :
Visual acuity was inferior to 20/50. There was a correlation between visual acuity and maximal motor level in PMD children. In PMD children, we found an elevated radial diffusion and a lowered fractional anisotropy compared to controls (p<0.05) in optic radiations, white mattered cerebellum and pons, showing myelin damage in these structures. There were no difference of anisotropy in calcarine cortex between PMD children and their parents. The nystagmus diminished after 6 years whereas ataxia and choreoathetosic movements developed. Optic atrophy did not appear before the age of 3 years and its importance (optic palor, partial or total atrophy ) was correlated with maximal motor level.
Conclusions: :
Ophthalmologic impairment in PMD disease is a model showing the link between visual acuity and cerebral myelination including myelination of cerebellum and pons controlling postural acquisition. DTI is a very good tool to quantify myelination in all dysmyelinating diseases.
Keywords: visual impairment: neuro-ophthalmological disease • vision and action • nystagmus